STREET BASIN - University of South Florida Clevel… · evaluation process which takes into account...

CLEVELAND STREET BASIN DRAINAGE STUDY

STORMWATER MANAGEMENT DIVISION DEPARTMENT OF PUBLIC WORKS - .

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CITY OF TAMPA, FLORIDA

POST , BUCKLEY , SCHUH & JERNIGAN INC. CONSULTING ENGINEERS PLANNERS LANDSCAPE AR~HITECTS

Post, Buckley Schuh 8 Jernigan, Inc. j CONSULTING ENGINEERS and PLANNERS

SUITE 245, HORIZON BUILDING. 451 1 NORTH HIMES. TAMPA, FLORIDA 33614.7070 813877.7275 TELEX 800435

September 8, 1983

M r . Ron Giovannelli , Chief Stormwater Management Division City o f Tampa 315 E. Kennedy 81vd. Tampa, Flori da 33602

Dear Mr. Giovannelli:

We are pleased to s u b m i t t h i s final report on our study of t h e Cleveland Street dra inage b a s i n .

En this report, we have i n v e n t o r i e d the existing drainage system, analyzed t h e causes o f current flooding i n the system through computer analysis and have developed and modeled t w e l v e a1 ternative solutions. Through an evaluation process which takes i n t o account estimated costs, water q u a l i t y impacts and performance, we have recornended a preferred solution to the f l o o d i n g problems i n t h e Cleveland Street Basin. As part o f our recommendations, we have proposed a phasing schedule for implementat ion o f the recornended plan, t o g e t h e r wi th a n t i c i p a t e d costs f o r each phase.

We appreciate this opportunity to carry out t h i s assignment f o r the City o f Tampa as well as the e x c e l l e n t cooperat ion and support we received from t h e City's Storm Water Management staff during the preparation of t h i s report.

Very truly yours,

POST, BUCKLEY, SCHUH & JERNIGAN, I N C .

Garth Horne, P.E. Project Manager

Prepared For :

The City o f Tampa

CLEVELAND STREET BASIN

DRAINAGE STUDY

September, 1983

Prepared By:

Post, Buckley, Schuh & Jernigan, Inc. Consulting Engineers & Planners 4511 N. Himes Aye., Sui te 245

Tampa, Florida 33614 (813) 877-7275

EXECUTIVE SUMMARY

The City of Tampa, through its Stormwater Management Division, has initiated a series o f comprehensive stormwater management studies throughout the City with the major objectives o f a1 levi at ing severe flooding problems whi le maintaining acceptable water qua1 i ty standards in receiving waters. The preparation of the Cleveland Street Basin study was authorized by Work Order No. 1, dated October 19, 1982, issued under Contract 2411-H, dated October 18, 1982 between the City of Tampa and Post, Buckley, Schuh & Jernigan, Inc., Consulting Engineers and Pl anners .

The objectives of this study were to inventory the existing Cleveland Street Basin drainage facilities, analyze the performance and adequacy of the system through computer model simulation, identify t h e causes of recurrent flooding wherever such flooding occurs during relatively minor rainfall events and recornend, after evaluating a variety of possible alternatives, a preferred cause of remedi a1 action, based on economic, environmental, feasibility and performance considerations.

City of Tampa records indicate that significant flooding occurs throughout the e x i s t i n g system during rainfall events which are f a r less severe than the desirable design storm for City drainage facilities. The major cause o f this flooding is the overtaxing of the b a s i n ' s major conveyance system, which was originally designed and constructed to handle runoff from a slightly smaller and much less intensely developed urban area than tha t which is now served by the system.

An i nventory of the exi s t i n g dr ai nage f ac i 1 it i es was accornp 1 i shed by researching the City o f Tampa design and as-bui It drawings, Florida Department of Transportation as-builts and by field survey. Basin and sub-basin boundaries were determined by review of recent aerial topography, the C i t y of Tampa drainage atlas sheets and, in questionable areas, field observation or survey.

Due to the complexity o f the Cleveland Street drainage system, computer model i ng techniques were employed to determine the performance and adequacy o f the existing system and evaluate alternative improvements to the existing system. A review of exi sting non-propri atory stormwater models revealed t h a t t h e hydrologic analysis of the Cleveland Street Basin could best be accomplished us ing the HEC-1 hydrologic program. Due to the extreme complexity o f t he Cleveland Street Basin drainage system, the hydraulic program EXTRAN was selected for the hydraulic analysis. To model the basin

I runoff hydrographs were simulated with the HEC-1 computer program. These hydrographs were then input to the EXTRAN program which simulated, on a real time basis, the hydraulics of the Cleveland Street Basin pipe network.

In order to verify these programs and calibrate the models developed for the Cleveland Street Basin, a gauging station was established at a manhole in

I t h e vicinity of t h e Cleveland Street and Clark Avenue intersection to record stormwater flows i n the system. This flow data was then utilized to ad jus t hydrologic and hydrau 1 i c model input parameters unt i 1 the simulated results of t he models agreed, within a reasonable degree o f accuracy, with the measured

I f l o w s . Once calibrated, t h e models were then ready to analyze the performance and adequacy o f t he existing facilities f o r the design event. The design

event selected, based on a review of literature and current City policy was the five year, one and one-half hour duration event totaling three and three tenths inches o f rainfall. Model simulation results of the design rainfall confirmed that the exi sting drainage f aci 1 i t i e s are severely overtaxed. Significant amounts of flooding were indicated by the model to occur alon Cleveland Street, west o f Grady Street; east of Himes Avenue, both north an south o f Kennedy Boulevard; and, in the comnerci a1 areas o f Westshore.

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Based on the results o f the existing condition simulation for the design rai nf a1 1, twe 1 ve improvement a1 ternat i ves were developed to part i a1 1 y or totally a l l e v i a t e significant flooding in the basin for the design event. Three of these alternatives el imi nates a1 1 significant flooding within the basin for t h e design event. For each of the twelve alternatives, order of magnitude c o s t estimates were developed and water quality impacts on ultimate receiving waters evaluated. The twelve a1 t e r n a t i v e s were then jointly reviewed by City of Tampa staff and PBS&J and a preferred alternative was selected after weighing implementation cost, environmental impacts, feasi b i 1 i ty and performance of each a1 ternative.

The preferred a1 ternat i ve for the Cl eve 1 and Street Basin wou Id e 1 imi nate all significant flooding within the bas in at an estimated cost of $10,270,000 and could be implemented in four, phases ranging in cost from $1.5 to $4.3 mi l 1 ion. The preferred a1 ternat i ve i nc 1 udes :

o Construction of a new separate outfall for the Westshore area to accommodate the intense development that has occurred since design and construction o f the existing system.

o Removal o f utility conflicts and placement o f an epoxy liner i n the Cleveland Street box culvert f r o m Himes Avenue to the outfall.

o Construction of detention facilities and associated minor pipe improvements as shown on Figure 4-11, Page 4-14, Alternative 12, Fac i 1 i ty Schematic.

This is the most economical of the three alternatives developed which would entirely eliminate a1.l flooding in the basin during t h e design event and would result in an estimated eighteen percent reduction in pollutant loading at the outfall. This preferred solution also has the advantage of being suited to phased implementation.

The phasing plan recormended for constructing the proposed improvements in t he Cleveland Street Basin includes four major phases:

1. Improve flow conditions i n the existing box culvert and construct a new outfall for Westshore. Estimated cost = $1,500,000.

2. Construct detention facilities and associated pipe improvements in the area east o f Himes Avenue and south of Kennedy Boulevard. Estimated cost = $2,600,000.

3. Construct detention facilities and piping in the area east of Himes Avenue, north of Kennedy Boulevard and i n the vicinity of - Grady Avenue and Cl eve 1 and Street. Estimated cost = 54,300,000.

4. Construct detention facilities and piping to serve the Westshore area. Estimated cost = $1,910,000.

TABLE OF CONTENTS

SECTION TITLE PAGE

Let ter o f Transrni ttal i i

Executive Summary

Table o f Contents

List of Tables

L i s t o f Figures

INTRODUCTION

1.1 Background 1 .2 Authori z a t i on 1 .3 Purpose and Scope 1 . 4 Agency Roles 1 . 5 Study Coordination A c t i v i t i e s

INVENTORY OF E X I S T I N G SYSTEM

2 . 1 H i stor i cal F 1 oodi ng: Records and Causes 2 .2 Topography 2.3 Land Use 2.4 Conveyance System General Characteri s ti cs 2.5 Measurement o f Flows i n Existing System 2.6 Water Quality Data Review

ANALYSIS OF THE EXISTING SYSTEM

3 . 1 Se lect ion o f Appropriate Model s 3.2 Storm Parameters

3.2.1 Source o f Rainfall 3.2.2 Recurrence In te rva l s - . - . . . . . -

3 .2 .3 Storm Durations 3 .2 .4 Rainfall Distr ibut ion

3 . 3 Tabu1 at i on o f Conveyance System Data 3 . 4 Preparation o f Model Input

3 . 4 . 1 Hydroloqic Input Data Required f o r HEC-1 3-8

3.4.1.1 Delineation o f Subbasins 3-8

TABLE OF CONTENTS (Cont.)

SECTION TITLE PAGE

3.4.1.2 Determination o f Impervious Areas 3-8 3.4.1.3 Time o f Concentrat ion 3-13 3.4.1.4 I n i t i a l Abs t rac t i on and Uniform

Loss Rate 3-13

3.4.2 Hydrau l ic Data Required f o r EXTRAN 3-13

3.4.2.1 Link/Node Map 3-13 3.4.2.2 Physical Charac te r i s t i cs o f System

Components 3- 16 3.4.2.3 Ambient Condi t ions 3-16 3.4.2.4 I n f l o w Hydrographs 3- 16 3.4.2.5 System Losses 3- 16 3.4.2.6 Adjustments 3- 17

3.5 Model Calibrat ion 3- 17

3.5.1 V e r i f i c a t i o n o f EXTRAN Model 3.5.2 C a l i b r a t i o n o f Hydrologic I n p u t Data

3.5.2.1 P r e c i p i t a t i o n Losses i n Pervious Areas 3-18 3.5.2.2 Irnpervi ous Areas 3-22

3.5.3 Cal i b r a t i on o f Hydraul i c Input Data 3.5.4 Calibration Resul ts

ANALYSIS OF SYSTEM ALTERNATIVES 4- 1

4.1 Problem Areas 4.2 System Improvement Types Ava i l ab le 4.3 A1 t e r n a t i ves Considered 4.4 Modeling o f Cont ro l A l t e r n a t i v e s 4.5 Water Q u a l i t y Assessment

4.5.1 Peak Flows 4- 15 4.5.2 Detent ion Times and P o l l u t a n t Load Reductions 4- 15 4.5.3 Shock Loading 4-15 4.5.4 Summary o f Water Qua1 i t y Eva1 u a t i o n 4-19

4.6 Eval u a t i on o f A1 t e r n a t i ves

CONCLUSIONS AND RECOMMENDATIONS

5 . 1 S e l e c t i o n o f the P r e f e r r e d A l t e r n a t i v e 5.2 DER Response 5 . 3 F inanc ia l Requirements and Phasing

APPENDIX A Minor Losses

LIST OF TABLES

TAH LE TITLE PAGE

2 - 1 Estimated Runoff P o l l u t a n t Loads f r o m t h e Cleveland Street Basin

3- 1 Model Summary 3-3

3- 2 Model Eva1 u a t i on Matr ix 3-4

4- 1 Comparison o f Computed Peak Flows and Flooding Improvements f o r Various A 1 t e r n a t i ves during the Design Storm

4- 2 Estimated Runoff Pollutant Loads from the Cleveland Street Basin f o r t h e Various A l t e r n a t i v e s 4-18

4- 3 Summary o f Alternate Improvement Es t imates 4-21

4-4 Summary o f Eva1 u a t i o n Criteria 4-22

5- 1 Proposed Phasing P I an 5-5

LIST OF FIGURES

FIGURE TITLE PAGE

1- 1 Cl eve1 and Street Basin Location Map 1- 2

1- 2 Task Cornpl e t i on Schedul e 1-4

2-IW F lood Prone Areas (West) 2- 2

2- 1 E Flood Prone Areas (East ) 2- 3

2- 2 Cl eve1 and Street Roadway Prof i 1 e 2-5

2- 3W Zoning (West) 2- 6

2-3E Zoning (East) 2- 7

2-4 Facility Schematic 2-8

2-5 Cl eve1 and S t r e e t and Clark Avenue Rating Curve 2- 10

3- 1 Dimensionless Hydrograph 3- 5

3- 2 Cumul a t i ve Rai n f a l 1 Hyetograph 3-7

3-3W Exist ing F a c i l i t i e s (West) 3-9

3-3 E Exist ing Facilities (East) 3- 10 i

Exi s t i ng Faci 1 i t i e s w i th Subbasi n Overlay (West)

Exist ing Faci 1 i t i e s w i t h Subbasi n Over1 ay (East)

L i nk/Node Map (West)

L i n k/Node Map (East )

January 20, 1983 Cal i b r a t i on Event - Rai n f a l 1 D i s tri b u t i on

February 2, 1983 Gal i brat i on Event - Rai nfal 1 D i s t r i but i on

February 2, 1983 Cal ibrat ion Event - Flow Hydrograph

February 2, 1983 Cal ibrat ion Event - E l e v a t i o n Hydrograph

January 20, 1983 Calibration Event - Flow Hydrograph

January 20, 1983 Calibration Event - Elevation Hydrograph

Probl em Areas

v i i i

LIST OF FIGURES (Cont. )

FIGURE TITLE PAGE

4- 2 A1 ternat ive 1 4-4

4- 3 A1 ternati ve 2 4- 5

4-4 A? ternative 4 4- 6

4- 5 A1 ternati ve 5 4-7

4-6 A1 ternati ve 6 4- 8

4- 7 A1 ternati ve 7 4-9

4- 8 A 1 ternati ve 8 4-11

4- 9 A 1 t e r n a t i ve 9 4- 12

4- 10 A 1 t e r n a t i v e 10 4-13

4- 11 A l t e r n a t i v e 12 4-14

5- 1 W Link/Node Map Preferred A 1 t e r n a t i ve Improvements (West)

5-1E Link/Node Map Preferred A1 t e r n a t i ve Improvements (East )

Sect ion 1

INTRODUCTION

1.1 BACKGROUND

The City o f Tampa, through i t s Stormwater Management D i v i s i o n , has i n t i t i a t e d a se r ies o f comprehensive stormwater management s tud ies throughout the City w i t h two major ob jec t ives ; t o a l l e v i a t e severe f l o o d i n g problems wherever they e x i s t ( o r have the p o t e n t i a l t o occur) and t o main ta in acceptable water q u a l i t y standards i n r e c e i v i n g waters. This study o f t he hydro log ic , hyd rau l i c and water q u a l i t y c h a r a c t e r i s t i c s of the Cleveland Street Basin i s an impor tan t f i r s t s tep i n t h e implementat ion o f t h e C i t y ' s program. The l o c a t i o n o f t he bas in i s shown i n F igure 1-1.

1.2 AUTHORIZATION

Preparat ion o f t he Cleveland Street Basin study was author ized by Work Order No. 1, dated October 19, 1982, issued under Contract 2411-H, dated October 18, 1982 between the City o f Tampa and Post, Buckley, Schuh & Jernigan, Inc. , Consul ti ng Engineers and Planners (PBS&J).

1 . 3 PURPOSE AND SCOPE

The ob jec t i ves o f t h i s study were t o i nven to ry t h e e x i s t i n g Cleveland Street Basin d r a i nage f a c i 1 i ti es , analyze the performance and adequacy o f t h e system through computer model simul a t i o n , i d e n t i fy t he causes o f recu r ren t f 1 oodi ng wherever such f l o o d i n g occurs d u r i n g re1 a t i v e l y m i nor r a i n f a l l events and recommend, a f t e r eva lua t i on o f a v a r i e t y of poss ib le a l t e r n a t i v e s , a p r e f e r r e d course o f remedi a1 ac t i on , based on economic , envi ronmental , f e a s i b i 1 i ty and performance considerat ions.

The i n i t i a l i t e m o f work undertaken by P8S&3 was the development o f a Plan o f Study d e t a i l i n g t h e scope o f work t o be performed, the i npu t da ta requ i red and output f o r each t a s k i n the study. The major tasks performed i n o rder t o achieve the sta ted ob jec t i ves o f the study were:

O Meetings w i t h representa t ives o f t he F l o r i d a Department o f Environmental Regulat ion (DER) t o o b t a i n t h e i r i n p u t re1 a t i v e t o w a t e r qua1 i t y considerat ions, acquai n t them w i t h the scope and purpose o f t h e study and t o asce r ta in their requirements f o r o b t a i n i ng environmental approval for proposed a1 t e r n a t i ve system improvements.

0 I nven to ry of t he e x i s t i n g Cleveland S t r e e t Basin drainage system through 1 ocat ion, tabu1 a t i o n , f i e 1 d surveying and v e r i f i c a t i on of design and a s - b u i l t drawing in fo rmat ion a v a i l a b l e f r o m City o f Tampa records.

Se lec t i on o f t he most appropr ia te computer model(s) f o r ana lys i s o f t h e C l eve1 and S t r e e t system.

H/L LSBOR ww

- CITY LIMITS

O Tabulat ion o f e x i s t i n g Land Use informat ion, de terminat ion o f stormwater r u n o f f i n p u t parameters and establ ishment o f design s t o r m c r i t e r i a .

O Preparat ion of model i n p u t data, v e r i f i c a t i o n o f t h e model and c a l i b r a t i o n o f t h e Cleveland Street system.

O Model i n g o f Contro l a l t e r n a t i v e s , assessment o f t he water quality, l and a c q u i s i t i o n and cos t impacts of each a l t e r n a t i v e and s e l e c t i o n o f t he preferred a1 t e r n a t i ves.

1.4 AGENCY ROLES

Throughout t h e progress o f t h i s study, PBS&J has worked c lose ly w i t h the staff o f the City o f Tampa Stormwater Management D i v i s i o n concerning s e l e c t i o n o f appropr ia te c r i t e r i a , method01 ogy t o be employed and c r i t i c a l dec is ions a f f e c t i n g t h e course of t h e study. I n add i t i on , representa t ives o f t h e DER were consu l ted a t appropriate p o i n t s i n the study t o help assure t h a t the system improvements u l timatel y selected woul d p rov ide an envi ronmental ly acceptable so lu t i on .

I

1 . 5 STUDY COORDINATION A C T I V I T I E S

The schedule o f a c t i v i t i e s f o r t he Cleveland Street Basin Drainage Study, shown i n F igure 1-2, i n d i c a t e s t h e sequential r e l a t i o n s h i p o f t h e var ious tasks undertaken d u r i n g the course o f t he study. I n con junc t ion w i t h these a c t i v i t i e s , two a d d i t i o n a l programs authorized by t he C i t y o f Tampa p rov ided va luab le i n p u t t o the Cleveland Street Study. The f i r s t o f these was t he Nationwide Urban Runoff Program (NURP) Study which es tab l ished water q u a l i t y data which was reviewed du r ing t h e evaluat ion o f the environmental impacts o f proposed a1 t e r n a t i ves. The second was a C i ty-wide data c o l 1 e c t i on e f f o r t which prov ided stage e l e v a t i o n and f l o w da ta u t i 1 i zed t o c a l i b r a t e t h e e x i s t i n g Cleveland S t r e e t system.

Sect ion 2

INVENTORY OF EXISTING SYSTEM

2.1 HISTORICAL FLOODING: RECORDS AND CAUSES

A 1 though 1 i t t l e t echn ica l data i s a v a i l a b l e concerning h i s t o r i c a l f l o o d i n g i n the Cleveland S t r e e t Basin, C i t y o f Tampa records i n d i c a t e that s i g n i f i c a n t f l o o d i n g occurs throughout the e x i s t i n g system du r ing r a i n f a l l events which a re f a r l e s s severe than the des i rab le design storm f o r C i t y drainage f a c i l i t i e s . F igures 2-1W and 2-1E present an o v e r a l l map o f t he system i nd i c a t i ng those areas i n which these f 1 oodi ng occurrences are mos t prevalent .

The major cause o f t h i s f l o o d i n g appears t o be over tax ing o f t h e b a s i n ' s major conveyance system which was o r i g i na l ly designed and cons t ruc ted t o handl e r u n o f f from a s l i g h t l y smal le r and much l e s s i n t e n s e l y developed urban area than that which i s now served by the system.

The Cleveland Street outfall was o r i g i n a l l y designed by F l o r i d a Department o f Transportat ion, FDOT, i n 1956 through a j o i n t agreement between the FOOT and t h e C i t y o f Tampa and was const ruc ted concu r ren t l y w i t h the Kennedy Boulevard (S. R. 60) improvements west o f Dal e Mabry H i ghway. A number of factors render that design inadequate t o handl e the r u n o f f f r o m t h e bas in as i t e x i s t s today:

O Runoff c o e f f i c i e n t s used f o r design i n t h e basin, which was re1 a t i v e l y sparsely developed i n 1956, ranged from 0 . 2 1 t o 0.30 and averaged about 0.25. As a r e s u l t o f t h e development which has occurred i n the area s ince t h a t t i m e , t he average r u n o f f c o e f f i c i e n t f o r t h e basin has increased t o approximately double that f igure. I n June, 1980 t h e Tampa Department o f Pub l i c Works est imated the ac tua l r u n o f f c o e f f i c i e n t t o be 0.51. Th i s f a c t o r alone would double t h e quantity o f stormwater r u n o f f f l o w i n g t o the Cleveland S t r e e t system.

Whereas t h e t o t a l area considered i n t he o r i g i n a l design of t h e o u t f a l l was 994 acres, the area which now con t r i bu tes t o t he Cleveland Street system i s est imated a t approximately 1,100 acres.

O The design storm used t o design the system i n 1956 was a th ree year frequency event. Current Tampa c r i t e r i a i s - t o design drainage f a c i l i t i e s adequate t o accommodate a f i v e year event.

0 The storm i n t e n s i t i e s r e f l e c t e d i n r a i n f a l l curves have increased s ince .the date o f t h e o r i g i n a l design. This increase i s a t t r i b u t a b l e t o a combinat ion o f a g rea ter amount o f s t a t i s t i c a l data on which t o base the curves, t he development s ince that t ime o f curves based on s p e c i f i c data f o r t he Tampa region and, perhaps, some c l i m a t i c change i n t h e p e r i o d s ince 1956.

Construct ion o f t h e Cleveland S t r e e t o u t f a l l was accomplished i n t h e late 1950s. Apparent ly, the system handled t h e drainage requirements of t h e bas in adequately u n t i 1 t he l a t e 1960s. I n 1969, t h e City began t o rece i ve

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INTERSTATE HWY 276

POST, 8UCKLEYj SCHUH & JERNIGAN, INC. CONSULTING ENGINEERS 8 PLANNERS

CLEVELAND STREET BASIN (WE-ST) U TAMPA. FLORIDA- FLOOD PRONE AREAS

DEPARTMENT BLIC WORKS ,

DATE: 11.a JOB NO. 5 r n - 2 0 1 , o o STORMWATER MANAGEMENT DIVISION

-, POST, BUCKLEY, SCHUH & JERNIGAN, INC. CLEVELAND STREET BASIN (CAST) CONSULTING ENQINEERS 8 PLANNERS

FLOOD PRONE AREAS u T A W * , ,,,,A

DEPARTMENT OF PUBLIC WORKS DATE n c u JOD ~ m . 17a-10 1.00 ;STORM WATER MANAGEMENT DJVlSlON

I C L l l I. .LET

complaints concerning over f low of t he system f r o m res iden ts who experienced f l o o d i n g i n the s t r e e t s , t h e i r yards and, i n some cases, t h e i r homes. Since t h a t t ime , as development progressed i n the basin, f l o o d i n g has become more frequent and severe.

A rev iew o f t h e C i t y ' s f i l e s concerning t h e Cleveland S t r e e t system revea ls t h a t areas where complaints from res iden ts i n d i c a t e tha t f lood ing i s most severe i nc lude the v i c i n i t y o f Westshore and Cleveland S t ree t , C la rk Avenue and Cleveland and on P l a t t Street, j u s t south o f the i n t e r s e c t i o n o f Krenta l Avenue and C l eve1 and.

2.2 TOPOGRAPHY

Three b a s i c sources o f i n fo rma t ion were u t i l i z e d t o determine the topographical fea tures o f t he Cleveland Street Basin. The f i r s t source used was Drainage A t l a s maps a v a i l a b l e from the City o f Tampa which i n d i c a t e d e leva t i ons a t street i n t e r s e c t i ons w i t h i n the bas i n and general d i r e c t i ons o f over1 and f 1 ow. The second e x i s t i ng source was topographical maps prov ided by the Southwest F l o r i d a Water Management D i s t r i c t (SWFWMO), i n d i c a t i n g e x i s t i n g one f o o t contours. PBS&J supplemented t h i s data i n areas where necessary t o de l i nea te subbasin boundaries by f i e l d i nspec t i on and/or f i e l d surveys.

One s i g n i f i c a n t topographical f ea tu re of t h e bas in was found t o be t h e r e l a t i v e l y sudden drop i n t h e p r o f i l e o f Cleveland Street between Church Avenue and Hale Avenue. I n t h i s area, t h e e x i s t i n g sur face e leva t i ons f a l l f r o m 22.9+ ft. t o 11.8k ft. i n a d is tance o f approximately 1,000 feet . A p r o f i 1 e o f t h e Cleveland S t r e e t roadway from Hirnes Avenue t o Occident Street, which displays t h i s sudden drop i n ground e levat ions , i s presented i n F igure 2-2. Eas t o f Church Avenue, t he basin i s extremely f l a t , ranging i n e l e v a t i o n f rom 20 t o 23 feet over a d is tance o f approximately one m i le . West o f Hale Avenue, e l e v a t i ons general ty sl ope toward 01 d Tampa Bay.

2.3 LAND USE

Since the Cleveland Street Basin i s almost t o t a l l y developed, e x i s t i n g l and use i s best demonstrated by the a e r i a l zoning map o f t h e study area presented i n F igures 2-3W and 2-3E. I n general, the l and uses i n the area a r e p r i m a r i l y s i n g l e f a m i l y r e s i d e n t i a l w i t h heavy concentrat ions o f commercial development a long the major a r t e r i a l streets t r a v e r s i n g t h e s i t e and i n t h e Westshore area.

E x i s t i n g l and uses i n t h e bas in are almost u n i v e r s a l l y cons i s ten t w i t h those shown i n H i 1 lsborough County's Hor izon 2000 Land Use Plan. Except f o r t he a n t i c i p a t e d development (o r redevelopment) o f several pr ime commerci a1 sites w i t h i n the study area, very l i t t l e change i n l and use is expected i n t he foreseeable fu tu re . For t ha t reason, t he analyses prepared i n t h e development o f t h i s study were based on e x i s t i n g l a n d uses.

2.4 CONVEYANCE SYSTEM GENERAL CHARACTERISTICS

F igure 2-4 i n d i c a t e s the major drainage f a c i l i t i e s w i t h i n the basin. These f a c i l i t i e s comprise a c losed condu i t system connect ing smal le r feeder systems throughout t he bas in t o a major conveyance made up o f i n c r e a s i n g l y 1 arger

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FIGURE 2-2

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concrete box cu l ve r t s , loca ted i n t he r igh t -o f -way of Cleveland S t r e e t and u l t i m a t e l y o u t f a l l i n g i n Neptune Lagoon a t Neptune Way and Shore Crest.

East o f Himes Avenue, t he major drainage f a c i l i t i e s i n t he bas in cons i s t o f two para1 1 e l condu i t systems ; one serv ing the area no r th o f Kennedy Boul evard and t h e o the r serv ing t h e area south o f Kennedy Boulevard. The conf luence o f these two sytems occurs i n t h e manhole l oca ted a t the i n t e r s e c t i o n o f Hirnes Avenue and Cl evel and S t ree t .

From Himes Avenue westward t o Westshore Boulevard the system cons i s t s o f t h e box c u l v e r t i n Cleveland Street w i t h feeder systems from the nor th and south connect ing d i r e c t l y t o i t a t i n t e r m i t t e n t loca t ions . I n the Westshore area, a 1 arge feeder system, cons t ruc ted d u r i ng devel opntent o f t he Wes t s h o r e commerci a1 d i s tr ic t , discharges i n t o the C l evel and Street box c u l v e r t a t the i n t e r s e c t i on o f C l evel and S t r e e t and Occident.

2.5 MEASUREMENT OF FLOWS IN EXISTTNG SYSTEM

Through a separate work order , au thor ized by t he City, records o f f l o w i n the system were obta ined by f i e l d measurement. The da ta obta ined by these measurements was used t o c a l i b r a t e the model i n p u t parameters f o r generat ing r u n o f f f rom the s i t e and f o r conveyance c h a r a c t e r i s t i c s o f the e x i s t i n g drainage f a c i l i t i e s .

To ob ta in these measurements, a gauging s t a t i o n was es tab l ished i n t h e system a t a manhole l oca ted a t t h e i n t e r s e c t i o n of Cleveland Street and C la rk Avenue. The equipment used fo r measuring f l o w s was a Marsh McBirney M M I 265 record ing flowmeter which cont inuously monitored stage e l e v a t i o n and f l o w v e l o c i t i e s a t t h e gauging s t a t i o n and char ted t h e r e s u l t a n t f lows i n m i l l i o n ga l l ons per day (rngd) on a 24 hour, r e a l t i m e bas is . T h i s i n s t a l l a t i o n was i n place f r o m December 1, 1982 through February 15, 1983. Two s i g n i f i c a n t r a i n f a l l events occurred and were recorded du r ing t h i s per iod ; one on January 20, 1983 and one on February 2, 1983.

To supplement these measurements, PBS&J made and recorded f i e l d observat ions du r ing a r a i n f a l l event which occurred on March 7, 1983. The r e s u l t s o f these observat ions 1 a rge l y conf i rmed the data obta ined by t h e prev ious metered measurements. The r a t i n g curve developed f o r t he gauging s i t e based on these measurements i s presented i n F igure 2-5.

2.6 WATER QUALITY DATA REVIEW

On October 22, 1982, a meeting was h e l d among techn ica l s t a f f o f the C i t y o f Tampa, the DER and the consul tants. The DER s t a f f i n d i c a t e d t h a t s ince improvements i n t he Cleveland S t r e e t Basin w i 1 l n o t 1 i kely i n v o l v e dredging and f i 11 ing i n any surface waters, it would n o t be necessary t o conduct water q u a l i t y sampling and ana lys i s s tudies. Instead, t he DER suggested a comparison o f t h e peak o u t f l o w under e x i s t i n g cond i t i ons versus p r e d i c t e d peaks under var ious a1 te rna t i ves , and maki rig some qua1 i t a t i v e concl u s i ons on how t h e d i f f e rences i n f l o w cond i t i ons may a f f e c t water q u a l i t y . Such an eva lua t i on i s prov ided i n subsect ion 4.5, as p a r t o f t he eva lua t i on of a1 t e rna t i ves .

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CLEVELAND STREET BASIN CLEVELAND ST. AND CLARK AVE.

RATING CURVE FIGURE 2 - 5

The eva lua t i on i n subsect ion 4.5 i s limited t o the amount o f outflow generated and does not i nc lude t h e r e c e i v i n g lagoon. No water q u a l i t y data was a v a i l a b l e f o r t he lagoon. F i e l d observat ions i n d i c a t e t h a t i t i s a body o f wa te r w i t h very l i m i t e d f l u s h i n g and poor w a t e r q u a l i t y , a t l e a s t from an a e s t h e t i c s tandpoint .

I n t h e process o f becoming familiar w i t h r u n o f f cond i t i ons i n t he Tampa area, t h e consu l tan t s t a f f reviewed several draft repo r t s produced i n t h e NURP study:

o "Precipitation Q u a n t i t y and Qua1 i t y Data" (February, 1983)

0 "Runoff Charac te r i za t i on - Water Qual i ty and F l ow Data" (March, 1983)

0 "Contro l Tes t i ng - Water Qual i t y and F low Data" (March, 1983)

The r u n o f f c h a r a c t e r i z a t i o n study i nvo l ved sarnpt i n g a t f i v e (5) drainage basins which had a h igh degree o f homogeneity o f l and use w i t h i n them. The study bas i ns represented t h e fol 1 owi ng 1 and uses:

High dens i t y r e s i d e n t i a l (J. L. Young Apartments)

O Low dens i t y r e s i d e n t i a l w i t h f r i n g e s o f i n s t i t u t i o n a l and commercial ( W i 1 der D i t c h Basin)

O . I n s t i t u t i o n a l and low dens i t y r e s i d e n t i a l (North J e s u i t High School Basin)

O Low dens i t y r e s i d e n t i a l (Charter and Hardi ng)

O High dens i t y commercial (Norma Park D i t c h Basin)

The above report conta ins t a b l e s and the sampling r e s u l t s for var ious forms. The r e p o r t does n o t summarize t h e data i n a readily usable f o r m (such as po l 1 u t a n t toads per u n i t areas).

The c o n t r o l t e s t i n g r e p o r t i nvo l ved moni to r ing a t t h e f o l l o w i n g types o f c o n t r o l devices:

0 Deten t i o n l r e t e n t i on ponds (water q u a n t i t y and qua1 i ty)

O D r a i n f i e l d / t r e n c h systems ( q u a n t i t y only)

O D i t c h systems (quan t i t y only)

As i n the c h a r a c t e r i z a t i o n report, the data are presented i n t a b u l a r form b u t have n o t been summarized i n terms o f po l l u t a n t loads per u n i t area, nor i n terms o f percentage o f removal o f pol 1 u t a n t i npu t .

Thus, the above d r a f t r epo r t s do n o t read i l y pe rm i t the c a l c u l a t i o n o f annual p o l l u t a n t loads from the Cleveland S t r e e t Basin. It should be noted t h a t a

United States Geological Survey study t h a t would f a c i l i t a t e the use o f t h e NURP data f o r est imat ing pollutant loads has n o t been published, and therefore was not available. Accordingly, estimated pollutant loads for the Cleveland Street Basin have been determined from other sources and are presented as Table 2-1. Since very l i t t l e change in land use i s anticipated to occur in the bas in these pollutant loads will be used as a base f o r order o f magnitude pollutant load comparisons o f t h e various alternative solutions developed.

TABLE 2-1

ESTIMATED RUNOFF POLLUTANT LOADS FROM THE CLEVELAND STREET BASIN

Unit Pollutant Loadings, i n pounds per acre per year

AREA SUSPENDED BOD5 TOTAL TOTAL LAND USE (ACRES) SOL1 DS NITROGEN PHOSPHORUS

Single Fami ly Multiple Family Commerci a1

Pollutant Loadi nqs, i n pounds per year

Single Fami ly 682.33 52,471.18 3,548.12 914.32 122.82 Mul t i p l e Farni ly 45.42 11,759.24 899.32 440.12 32.23 Commerci a1 284.21 223,474.32 19,184.18 3,180.31 278.53

TOTALS 1,011.96 287,704.74 23,631.62 4,534.75 433.58

SOURCE:

j Jettmar , R. V. e t a1 . "Dynamic Water Qua1 i ty Model i ng i n Southeast F l ori da, "Journal o f the Environmental Engi neer i ng D i v i s i on , Arneri can Soc ie ty o f Ci v i 1 Engineers , February 1980.

i or Sect ion 3

i E ANALYSIS OF THE EXISTING SYSTEM

3.1 SELECTION OF APPROPRIATE MODELS

One o f t h e e a r l i e s t i tasks undertaken i n t h e course o f t h e Cleveland Street Basin study was t heose lec t i on o f the most appropr ia te model, or combination o f models t o be used fwr s imu la t i on o f t he hydrology and hyd rau l i cs o f the study area. F ina l mode1:coselection was accomplished by i d e n t i f y i n g the charac- t e r i s t i c s o f t he b * i n which e s t a b l i s h s p e c i f i c model requirements, rev iewing t h e capabi 1 i ty o f he range o f ava i 1 ab le models t o s a t i s f y those requirements and, through use a t r a n eva lua t i on ma t r i x , determin ing the most appropriate model s.

The s p e c i f i c drainage features o f the Cleveland S t r e e t Basin which d i c t a t e d t h e c r i t e r i a f o r t h ~ h o d e l s se lec ted inc lude:

A compl i mtkd, c losed conduit drainage network.

O A drai nagenetwork s e n s i t i v e to t a i 1 w a t e r condit ions.

The poss i t f i l i t y o f reverse f l o w occurring w i t h i n p o r t i o n s o f the sys tern.

O Surcharg ingwi th inthesystem.

* Var ia t ion in in subbasin lag t i m e s and t i m e displacement o f hydrograph peaks r e s u l t i n g f r o m t h e l i n e a r shape o f t h e basin.

Looped andrparal 1 e l pipe systems.

Other factors c o n s i c k e d i n the model s e l e c t i o n process were; a v a i l a b i 1 i t y o f t he model s on a nou-propri e t o r y bas i s , documentation, proven re1 i abi 1 i ty and the c o m p a t i b i l i t y o f d'nput requirements w i t h e x i s t i n g , a v a i l a b l e data.

Computer models c o ~ i d e r e d f o r t h e ana lys i s of t h e Cleveland Street Basin were :

StormwatedWanagement Model (SWMM)

O ILLUDAS ( f m m e r l y , Road Research Lab Model)

O SPEC Storm Drainage Model

O SCS T R 2 0

O EXTRAN

O RUNQUAL

The above l i s t of models was f u r t h e r screened based on a r ev i ew o f user manuals, discussions w i t h prior users and ava i lab1 e techn ica l papers concerning past model app l i ca t i ons . Th is r e v i e w r e s u l t e d i n narrowing t h e l i s t o f candidate models f o r the Cleveland Street Basin to f i v e ; SWMM, EXTRAN, RUNQUAL, TR-20 and HEC-1. The s i g n i f i c a n t fea tures o f these f i v e models a re tabu1 ated i n the Model Summary shown i n Tab1 e 3-1.

The f i n a l assessment o f the most appropr ia te models was made us ing the eva lua t i on m a t r i x shown i n Table 3-2.

As a resu l t o f t h i s eval u a t i on i t was determined t h a t hydraul i c simul a t i on o f t h e Cleveland S t r e e t Hasin would be accomplished us ing the EXTRAN model and basi n hydrology shoul d be developed w i t h HEC-1 u t i 1 i z i n g t h e SCS Dimension1 ess Hydrograph depicted i n F igure 3-1. As can be -seen from Table 3-2, EXTRAN i s t he o h l y a v a i l a b l e mode? considered which s a t i s f i e s a l l o f the hyd rau l i c c r i t e r i a es tab l ished f o r model se lec t ion . HEC-1 was chosen because o f t h e l i m i t e d amount of hydro log ic data a v a i l a b l e f o r t he study area and the model 's f 1 e x i b i 1 i t y i n genera t i ng i n f 1 ow hydrographs.

Oocurnentation i s excel l e n t f o r both models and t h i s wi 11 f a c i l i t a t e their use by C i t y s t a f f a f t e r t h e study has been completed.

3.2 STORM PARAMETERS

As noted i n Sect ion 1.1, the Cleveland Street Basin study i s p a r t o f a comprehensive C i ty -w ide study. I n order t o main ta in consis tency i n t h e methodology used and conclus ions reached i n a l l o f the on-going and f u t u r e ana lys i s o f basins throughout the City, a j o i n t meet ing was h e l d w i t h the Stormwater Management D i v i s i o n s t a f f on December 13, 1982 t o e s t a b l i s h a uniform s e t o f storm parameters t o be used du r ing the imp1 ementation o f t h i s program.

Dur ing t ha t meeting, t h e s p e c i f i c storm parameters discussed and the agreements reached concerning c r i t e r i a t o be u t i 1 i z e d i n these s tud ies were as f 01 1 ows :

3.2.1 Source o f Rainfall Data

F ive d i f f e r e n t sources were a v a i l a b l e f o r data concerning t h e re la t ionsh ip of r a i n f a l l i n t e n s i t i e s , frequencies and dura t ions i n t he Tampa region. These cons is ted o f the FDOT R a i n f a l l Curves f o r Zone 6, Un i ted States Weather Bureau Technical Paper 40, t h e P i n e l 1 as County Rai n f a l 1 Report, C u r i o s i t y Creek R a i n f a l l Analys is and the R a i n f a l l Quanti ty Analys is ( o r i g i n a l r e p o r t and supplementary data) prepared by t h e C i t y ' s consul tants f o r t he ongoing NURP study.

Because of t h e widespread use and t h e acknowledged r e l i a b i l i t y o f t h e FDOT curves, t h i s source was chosen as t h e approved source fo r rai n f a l 1 data.

TABLE 3-1 - MODEL SUMMARY

Model Advantages D i sadvantages Appl i cabi 1 i t y

SWMM O Comprehensive O S i z e O Where a simpler model w i l l no t work due t o size O Good documentation O Complexity and complexity (i. e. , hundreds o f pipes and O Users group O Large data requirement hydraul i c cont ro ls )

Frequent updates/irnprovements O High run t ime/cost O Quani ty and q u a l i t y addressed

Has been tes ted extensively O Tida l f low can be simulated

EXTRAN O Backwater e f f e c t s are ca lcu la ted O Complex O Where complex p ipe systems need t o be analyzed (Unl ike runof f and t ranspor t blocks) O No q u a l i t y

O Handles f low reversa l , surcharge O Handles looped connections

RUNQUAL Re la t i ve l y simple O Necessary t o p l o t i n v e r t s f o r pipes O Prel iminary design - pipes, channels, e tc . , w i th Can handle quanity and q u a l i t y and channels and hydrau l ic units and moderate complex i ty ' Allows evaluat ion o f peak f l ow a t determine predomi nent scope f o r each

moderately designed elements u n i t ( res ize opt ion) * W i l l on ly take c i r c u l a r pipes - Equiv.

diameters have t o be ca lcu la ted f o r others

F I P C O Simple O Necessary t o re-enter data f o r each Quick & accurate hydrau l ic p r o f i l e s on a segment- ' Quick sec t ion before re-running. Could be by-segment basis

F a i r l y accurate re-wr i t t e n t o e l i m i nate t h i s

TR-20 O Good documentation O Routing f o r pipes requires stage- " Hydro1 ogy O Widely used storage i n p u t a Routing f o r non-pipe systems

HEC-1 O Good documentation ' TR-20 type convex rou t i ng opt ion O Hydro1 ogy Support should be used f o r "what- i f " Routing Widely used s imula t ion only and not de ta i l ed

designs

HEC-2 a Good documentation Re la t i ve l y la rge amount o f data O Backwater analys is ' Support codi ng requi red

Widely used O Hand1 es i r r e g u l a r cross-sect i ons

TABLE 3-2

MODEL E V A L U A T I O N MATRIX

CLEVELAND STREET B A S I N MODEL C R I T E R I A

SWMM SWMM HYDRAULIC CRITERIA: TRANSPORT EXTRAN RUNQUAL

O Simulates complicated, c losed pipe networks *

O Backwater conditions jc

O Reverse F l o w R

O Surcharging A

Looped Systems R A

O In - l ine Storage * * A

O O f f - l ine Storage R k A

SWMM HYDDROLOGIC C R I T E R I A : RUNOFF RUNQUAL TR-20 HEC-1

* Routing Methods . - - . - - -

-Convex Methods (SCS) R A A

-Kinematic Wave Method A A

- I n i t i a l & Uni fo rm Loss k * . . ---

-Exponential L o s s Rate * R

-SCS Curve Numbers * A

O Depression Storage

Relat ive Simplicity o f Input Data A A

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CLEVEIAND ST-REET BASIN DIMENSI ONLESS HYDROGRAPH

FIGURE 3-1 v

3.2.2 Recurrence I n t e r v a l s

A major dec i s ion i n t h e s e l e c t i o n o f storm parameters i s t h a t o f recurrence i n t e r v a l s . This dec i s ion determines, t o a large extent , t he l e v e l o f p r o t e c t i o n aga ins t f 1 oodi ng t h a t w i 1 1 be prov ided by the recommended improvements i n the drainage system. Recurrence i n t e r v a l s used f o r d r a i nage design o f r e s i d e n t i a l streets are u s u a l l y two t o t h r e e years while somewhat more i ntense (1 ess f requent) storms are general l y appl i ed f o r major a r t e r i a1 s. I n t he City of Tampa a f i ve -yea r frequency storm i s t he accepted c r i t e r i a f o r roadway drainage design. The r e f ore, t h i s recurrence i n t e r v a l was agreed upon as the c r i t e r i a t o be used for condu i t system design i n Cleveland S t r e e t and o t h e r ongoing s tud ies . I n o rder t o p rov ide a d d i t i o n a l p r o t e c t i o n , i t was f u r t h e r e s t a b l ished t h a t storms w i t h a recurrence i n t e r v a l o f 25 years would be appl i e d t o major de ten t i on ponds and 50 years t o r e t e n t i on ponds.

F o r t he Cleveland S t r e e t Basin on l y the 5 year recurrence i n t e r v a l storm was considered s i nce the bas i n i s predorni nan t l y a c l osed condu i t conveyance system and the re fo re can be c l a s s i f i e d as a conveyance dependent bas in as opposed t o a storage o r volume s e n s i t i v e basin. Any de ten t i on f a c i l i t i e s proposed f o r the bas in w i l l be viewed as secondary improvements t o the e x i s t i n g pr imary conveyance system.

3 . 2 . 3 Storm Durat ions

An a t tempt was made t o s e l e c t a standard s t o r m du ra t i on t o be used i n a l l drainage s tud ies be ing prepared f o r the C i t y . Durat ions from three t o seventy- two hours were consi dered. However, a f t e r a lengthy d i scussi on, i t was agreed t h a t t he c r i t i c a l storm du ra t i on should be es tab l ished f o r each i n d i v i d u a l bas in based on i t ' s unique hydro1 ogic and hyd rau l i c charac ter - i s t i c s .

For t he Cleveland S t ree t Basin storm du ra t i ons o f one-half hour, one hour, one and one-hal f hours, two hours, t h r e e hours and s i x hours were s imulated du r ing t h e c a l i b r a t i o n phase. Based on the s imu la t i on r e s u l t s f o r these d u r a t i o n events the one and one-half hour du ra t i on was determined t o be the appropr ia te c r i t i c a l dura t i on event.

Rai nfal l D i s t r i b u t i o n

Several r a i n f a l l t ime d i s t r i b u t i o n pa t te rns were considered f o r use i n t he C i t y drainage s tud ies . These i nc l uded SCS Rai n f a l l D i s t r i b u t i ons , Hu f f R a i n f a l l D i s t r i b u t i o n s , d i s t r i b u t i o n s found i n the C u r i o s i t y Creek Report and the p a t t e r n developed by t h e C i t y ' s consul tants f o r t he Tampa NURP Study. A f t e r some d iscussion, it was agreed that, since t h e p a t t e r n used i n t h e NURP Study was based on a s t a t i s t i c a l eva lua t ion o f every s i g n i f i c a n t recorded event i n t h e Tampa area over a 22-year per iod , t h i s source prov ided t h e mos t re1 iable rai n f a l 1 d i s t r i b u t i o n data c u r r e n t l y avai I ab le . T h i s p a t t e r n i s presented i n F igure 3-2 f o r the 5 year recurrence i n t e r v a l .

3 . 3 TABULATION OF CONVEYANCE SYSTEM DATA

The i n i t i a l source o f data used by PBS&J t o inventory the e x i s t i n g drainage f a c i l i t i e s i n the Cleveland S t r e e t Basin was the Drainage A t l a s maps mai ntai ned by the City Stormwater Management D iv i s ion . These maps i nd i ca te

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CLEVEUND STREET BAS1 N CUMULATIVE RAINFALL HY ETOGRAPH

5 YEAR RECURRENCE INTERVAL FIGURE 3-2

t he general l o c a t i o n and s i z e o f condui ts w i t h i n t h e system as we l l as the d i r e c t i o n o f over1 and f 1 ow.

I n order t o ob ta in more d e t a i l e d i n fo rma t ion about these f a c i l i t i e s , PBS&J researched the design and as-bui 1 t records avai 1 ab le i n t he f i l e s o f the City o f Tampa and, i n some cases, the FDOT. U t i l i z i n g these records, an E x i s t i n g F a c i l i t i e s Map was developed a t a sca le o f 1" = 200' i n d i c a t i n g the l oca t i on , s ize, l e n g t h and i n v e r t e l e v a t i o n o f a l l drainage f a c i l i t i e s 36 inches i n diameter o r l a r g e r throughout t h e system. Wherever condu i ts less than 36 inches i n s i z e were f e l t t o be s i g n i f i c a n t i n the ana lys i s o f t h e o v e r a l l system, they were also shown t o t h i s l e v e l o f d e t a i l . The E x i s t i n g F a c i l i t i e s Map i s presented i n F igures 3-3W and 3-3E. I n cases where de ta i 1 ed as-bui 1 t in fo rma t ion was n o t ava i l ab le , appeared quest ionable o r was n o t cons i s ten t w i t h cursory f i e l d observat ions, d e t a i l e d f i e l d observat ions were made and t h e map o f e x i s t i n g f a c i l i t i e s ad jus ted accordingly . I n a d d i t i o n , f i e l d surveys were conducted t o v e r i f y t h e l o c a t i o n and e leva t ion o f major system components and t o p rov ide answers t o quest ions which cou ld n o t be adequately resolved by f i e l d observat ion. Dur ing t h i s stage o f i n v e s t i g a t i o n , no at tempt was made t o i d e n t i f y o r 1 ocate u t i 1 i t y conf I i c t s o r o ther obs t ruc t i ons i n t h e system.

3.4 PREPARATION OF MODEL INPUT

3.4.1 Hydrologic Input Data Required f o r HEC-1

The HEC-1 model was used t o generate r u n o f f hydrographs f o r each subbasin i n the Cleveland S t r e e t Basin system. I n o rder t o develop the i n p u t data requ i red by HEC-1, the f o l l owing s e r i e s o f eva lua t ions was requi red:

3.4.1.1 Del i n e a t i o n o f Subbasi ns

The boundaries o f subbasins w i t h i n the study area were determined f rom a v a i l a b l e topographical data, supplemented by f i e ld observa t ion and, i n some instances, f i e l d survey. The d e l i n e a t i o n o f the subbasins, over layed on t h e E x i s t i n g F a c i l i t i e s Map, i s presented i n F igures 3-4W and 3-4E. U t i l i z i n g the subbasin map, p l o t t e d a t a sca le o f 1" = 200' , the area o f each subbasin was determined by p lan imeter measurement.

3.4.1.2 Determinat ion o f Imperv i ous Areas

A v i t a l i n p u t parameter i n t h e de terminat ion o f r u n o f f from any subbasin i s t he percentage o f t h e total area which i s impervious. I n o rder t o make t h i s determinat ion, a r i go rous ana lys i s was made o f each subbasin w i t h i n t h e Cleveland S t r e e t Basin t o measure, on recent a e r i a l photographs, r o o f , pavement and o the r areas considered t o be impervious t o water. This procedure was app l i ed t o r e s i d e n t i a l areas o f va ry ing dens i t y as we1 1 as t o commercial and pub1 i c o r i n s t i t u t i o n a l s i t e s w i t h i n t h e basin.

As t h e study progressed, i t became impor tan t t o d i s t i n g u i s h direct ly connected impervious areas ; i . e. , areas which c o n t r i b u t e stormwater r u n o f f d i rect'l y t o t h e drainage system, from non-d i rec t ly connected areas. Non-d i rec t ly connected areas a re de f i ned as impervious areas from which runo f f must f l o w across adjacent perv ious areas such as lawns or open f i e l d s p r i o r t o

I ' DATE: 1-#01 JOO No. 3 7 D - Y O l . 0 0 1 -O I I STORMWATER MANAGEMENT DIVISION I f0.. 1":-

POST, BUCKLEY, SCHUH & JERNIGAN, INC. IjsS( CONSULTING ENGINEERS a PLANNERS

u TAMPA. FLORIDA

CLEVELAND STREET BASIN (WEST)

EXlSTllG FACILITIES DEPARTMENT OF PUBLIC WORKS

I- POST, BUCKLEY, SCHUH & JERNIGAN, INC. CONSULTING ENGINEERS 8 PLANNERS

u ITAMPA. FLORIDA

DLTE: .Ill 4 0 0 H= III -20 1.00

CLEVELAND STREET BASIN (EAST)

EXlStlPlG FAClLlTlES

@

DEPARTMENT OF-PUBLIC WORKS 0 "..-a" " 0 I I GTORMWATER MANAGEMENT DIYISION I -

POST, BUCKLEY, SCHUH & JERNlGANt INC. CLEVELAND STREET BASIN (EAST) CONSULTING ENGINEERS & PLANNERS

TAMPA FLORIDA DRAINAGE SUB-BASINS

EXlSTlMG FACILITIES DEPARTMENT OF PUBLIC WORKS

I O A l E : # I 4 3 N k 470-20 1.00 I STORMWATER MANAGEMENT DIVISION 0 100 4 100

I C I L C I Y r r l l

3.4.2.2 Physical Charac te r i s t i cs o f System Components

For each l i n k and node i n t h e system, da ta was i n p u t d e f i n i n g the length , s i z e and shape o f a1 1 condui ts , i n v e r t e leva t i ons a t each node and the e leva t i ons o f condui ts a t each node r e l a t i v e t o t he node i n v e r t . E x i s t i n g ground e leva t i ons a t a1 1 nodes were a1 so defined. These e leva t i ons were taken f r o m t h e C i t y ' s Draingae A t l a s maps wherever such data was ind ica ted . I n those instances where e levat ions a t j unc t i ons were n o t shown on t h e a t l a s sheets, they were determined f r o m t h e SWFWMD contour maps.

3 .4 .2 .3 Ambientcond i t ions

The hyd rau l i c computations performed by EXTRAN take i n t o account e x i s t i n g t a i l w a t e r cond i t ions , t h e volume o f water s to red i n t he system and any ambient f lows a t t h e beginning o f the modeled event. For t he model runs made f o r t h e Cleveland S t r e e t Basin, e l e v a t i o n +2.0 was i n p u t as the assumed water e l e v a t i o n a t t h e o u t f a l l and i n i t i a l water depths were i n p u t a t t he downstream nodes consi s t e n t w i t h t h a t assumed el evat ion. Ambi en t f 1 ows were a1 1 de f i ned as zero.

3.4.2.4 I n f l o w Hydrographs

I n o rder t o i npu t the r u n o f f hydrographs generated by HEC-1 i n t o the EXTRAN model, a spec ia l computer program was developed t o conver t t h e HEC-1 output i nto a format w h i c h cou ld be accepted by EXTRAN. HEC-1 f low hydrographs a t each input node were p r i n t e d a t t h ree minute i n t e r v a l s f o r t he s imu la t i on per iod. HEC-1 output cons is ted o f t he inpu t node number and the corresponding tabu la ted f l o w hydrograph. To i n t e r f a c e HEC-1 w i t h EXTRAN it was necessary t o develop a program t h a t would rearrange t h i s ou tpu t t o r e f l e c t t h e tabu la ted f l o w s o f a l l i n p u t nodes a t each time step.

3.4.2.5 System Losses

Four types o f energy losses were taken i n t o account i n t he prepara t ion ' o f i n p u t data f o r EXTRAN; f r i c t i o n losses, connect ion losses, entrance losses at manholes and junc t i ons and losses due t o bends. F i e l d observat ions o f t h e age and c o n d i t i o n o f e x i s t i n g f a c i l i t i e s were made as a bas i s f o r eval u a t i ng the appropr ia te "n" values t o be used f o r f r i c t i o n losses. These values were then ad jus ted t o account f o r 1 osses a n t i c i p a t e d due t o connections , bends i n the system, manhole entrance cond i t i ons and obs t ruc t ions , which t y p i c a l l y occur i n urbanized storm sewer systems.

Losses associated w i t h connect ions , bends and entrance cond i t i ons were est imated u s i ng t h e procedures presented i n "Water Supply and Pol 1 u t i o n Cont ro l " , C la rk Viessman and Hammer, 1971. For each l i n k i n t h e system an "n" va lue represent ing f r i c t i o n , bend, connect ion and entrance losses was computed usings Manning's Equation. These "n" values were then compared t o t h e range of "n" values presented i n "Open Channel Hydraul ics" , Chow, 1959, f o r concrete 1 ined condu i t sewer systems. In most instances the est imated "n" values d i d f a l l w i th in the normal and maximum "n" value range presented by Chow f o r s t r a i g h t systems. Consequently, the "n" va lue range presented by Chow were deemed t o be app l i cab le t o t h e Cleveland S t ree t condu i t system and were genera l l y used except when i t was f e l t prev ious est imates j u s t i f i e d s l i g h t l y g rea te r values. Reference ma te r ia l f o r "n" value est imates are i nc luded i n Appendix A.

Dur ing t h e c a l i b r a t i o n phase adjustments t o the o r i g i n a l l y est imated 'In" values f o r the Cleveland S t r e e t box c u l v e r t were requ i red t o ga in c a l i b r a t i o n . These greater "n" values were f e l t t o be a t t r i b u t e d t o numerous u t i l i t y obs t ruc t i ons found t o e x i s t and a s l i g h t l y rougher box f l o o r .

3.4.2.6 Adjustments

Some adjustments t o the i n p u t data were requ i red t o accommodate c e r t a i n 1 i m i t a t i o n s o f t h e EXTRAN model. I n instances where p ipe s i z e increased w i t h i n a l i n k , the pipe was i n p u t as one s ize. Th is was accomplished by a d j u s t i n g t h e l eng th o f t he sho r te r pipe , keeping the "n" va lue constant, lo a l eng th t ha t would y i e l d t h e same hydraul i c 1 osses as those t h a t would occur i n the actua l system.

In some cases, t h e ac tua l l e n g t h between nodes cou ld n o t be i n p u t because i t was too sho r t . EXTRAN, which computes cond i t ions in the system a t spec i f i ed t i m e steps, requ i res t h a t each condu i t i n t he system be o f s u f f i c i e n t l eng th t o s a t s i f y t h e equat ion "Maximum Time Step ( i n seconds) = ~ /m" where L = the l e n g t h o f t he p ipe i n feet , D t he depth o f the p ipe i n f e e t and g i s t he g r a v i t a t i o n a l accel e r a t i on. Wherever i t was necessary t o inc rease pipe lengths t o s a t i s f y t h i s cond i t i on , an equ iva len t 'In" value (the c o e f f i c i e n t f o r f r i c t i o n losses i n t h e p ipe) was computed and i n p u t i n o rder t o assure t h a t f r i c t i o n losses would not be d i s t o r t e d .

3 . 5 MODEL CALIBRATION

I n order t o v e r i f y t he i n p u t da ta f o r t h e .Cleveland S t r e e t Basin, a s e r i e s o f steps was taken t o conf i rm t h a t t h e computer model was opera t ing c o r r e c t l y and t h a t t h e results obta ined from c a l i b r a t i o n runs o f the model agreed w i t h f i e l d measured data.

V e r i f i c a t i o n o f EXTRAN Model

The i n i t i a l s tep i n t h e c a l i b r a t i o n process was t o v e r i f y the EXTRAN model as i n s t a l l e d i n the PBS&J system. Th is was accomplished by i n p u t i n g a sample problem w i t h hyd rau l i c cond i t i ons s i m i l a r t o those known t o e x i s t i n t h e Cleveland S t r e e t system and o b t a i n i n g known, c o r r e c t r e s u l t s . The sample problem used was a smal l system c o n s i s t i n g o f f i v e condui ts and a r e s e r v o i r having free o u t f a l l . The r a i n f a l l event used was s u f f i c i e n t l y small so t h a t no surcharging occurred i n t h e sample run. The t ime step used f o r this sim- u l a t i o n was 20 seconds. The r e s u l t s obta ined from t h i s sample r u n were sa t - i sfac tory .

The second s tep taken t o v e r i f y the model was t o s imulate a minor event i n t h e Cleveland S t r e e t system. The event chosen was one-half i n c h r a i n f a l l over a one hour per iod . No t a i l w a t e r cond i t i ons were input . When t h i s event was modeled us ing a t e n second t ime step, i t d i d n o t produce surcharging i n t h e system and no problems were encountered.

Next, t h e same event was simulated, b u t i n t h i s run t a i l w a t e r cond i t i ons were in t roduced by s e t t i n g t h e e x i s t i n g water e l e v a t i o n a t the o u t f a l l a t e l e v a t i o n +2.0 and s p e c i f y i n g an ambient water depth f o r a l l nodes w i t h i n v e r t elevations lower than c2.0. As a r e s u l t o f t h i s t r i a l , i t was found t h a t t h e EXTRAN program does n o t automati ca? 1 y compute i n i ti a1 water vo l umes i n t h e p ipe system based on ambient depths. Consequently, t he volume o f water i n t h e system a t the beginning o f the event i s not considered when the program

3- 17 REPEO: E

ca lcu la tes t h e o v e r a l l mass c o n t i n u i t y o f t h e system ( the volume of stormwater en ter ing , s to red and l eav ing t h e system). However, a rev iew o f t he s imu la t i on r e s u l t s revealed t h a t t h i s m i nor inadequacy i n the program' s account i ng procedure d i d not a f f e c t t h e answers obta ined f o r t h e Cleveland S t r e e t system. The r e s u l t s of t h i s run a1 so revealed tha t , when modeling a system w i t h l a r g e condui ts and appreciable ambient depths, minor i n s t a b i l i t i e s can occur d u r i n g 1 ow f l o w cond i t ions .

F ina l ly, t h e model was t e s t e d us ing a one and one-half i n c h rainfall over a one hour per iod. Th i s event r e s u l t e d i n widespread surcharging throughout t h e system and ser ious model i n s t a b i l i t y . Based on rev iew o f t he EXTRAN program and d iscussions w i t h M r . Larry Rosener, one o f t h e authors o f EXTRAN, it was determined t h a t t h i s i n s t a b i l i t y was caused by the large number o f nodes surcharging simultaneously i n the Cleveland Street system, the l a r g e condu i t s izes w i t h i n the system and t h e i t e r a t i v e methodology used by the program du r ing surcharge.

One o f t h e bas ic equat ions used by EXTRAN t o compute heads and f lows a t each t ime step d u r i n g s imu la t i on o f an event is t he r e l a t i o n s h i p o f head d i f f e r e n t i a l ( A h l t o f l o w (Q) and t h e area o f t he water's sur face (A ) a t each node; i . e . , A h U Q/As. When condu i ts a r e f l o w i n g p a r t i a l ly f u l l , &TRAN computes the water sur face area i n each condu i t and assigns h a l f of t h i s area t o t he node a t e i t h e r end. However, d u r i n g surcharge, when the hyd rau l i c p r o f i l e i s above the crown o f t h e condui t , t h i s surface area becomes zero and t h e equat ion can no longer be appl ied. When t h i s c o n d i t i o n occurs, EXTRAN switches t o a d i f f e r e n t set of equations which approximate t h e s o l u t i o n through an i t e r a t i v e t r i a l and e r r o r process i n order t o f i n d a combinat ion o f heads and f l ows a t each node t h a t w i l l p rov ide a c o n t i n u i t y balance throughout t he e n t i r e system. This method i s successful when appl i e d t o smal l systems, b u t due t o t h e l a r g e number o f va r i ab les i n the Cleveland Street Basin, EXTRAN was unable t o converge and y i e l d accurate r e s u l t s .

I n o rder t o a1 l e v i a t e t h i s problem and e l im ina te the need f o r t he model t o solve by i t e r a t i o n , constant sur face areas t ha t f u n c t i o n as small surge tanks were i n t roduced a t each node. Th is a l lowed the program t o cont inue t o use t h e bas ic equations. I n i t i a l l y t he sur face area i n p u t was 500 square f e e t a t each node. Through a t r i a l process, these areas were u l t i m a t e l y reduced t o a minimum (as smal l as 50 square fee t ) . A comparison o f the r e s u l t s o f t h e program a t low f lows, w i t h and w i t h o u t t h e storage areas, i n d i c a t e d t h a t the impact of i n t r o d u c i n g these areas was minimal i n terms o f s imulated e leva t i ons and flows.

3 . 5 . 2 C a l i b r a t i o n of Hydrologic Input Data

F i e l d measurements taken du r ing two ac tua l storm events were u t i l i z e d t o c a l i b r a t e t h e hydro log ic and hyd rau l i c i n p u t data used f o r t he Cleveland S t r e e t Basin. The f i r s t o f these events occurred on January 20, 1983, du r ing which 0 . 5 1 inches o f r a i n was recorded. The second event, on February 2, 1983, measured 1.7 inches. The hyetographs developed t o represent r a i n f a l l d i s t r i b u t i o n d u r i n g these two events are shown i n F igures 3-6 and 3-7.

3.5.2.1 P r e c i p i t a t i o n Losses i n Pervious Areas

I n i t i a l l y , t h e r a i n f a l l events used f o r c a l i b r a t i o n were s imu la ted w i t h the HEC-1 model us ing a value o f one-hal f i n c h f o r bo th t h e I n i t i a l Abs t rac t i on

3- 18 REPZO: E

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2 5 I#= m z 2 F Q ~ ;g$ a g FJE :3;

spa d 2s > c u

3 5, 07

3.5.2.2 Impervious Areas

As noted i n t he d iscussion o f i n p u t parameters i n Sect ion 3.4.1.2, i t became apparent du r ing c a l i b r a t i o n t h a t the runoff c o n t r i b u t i o n from i n d i r e c t l y connected impervious areas was s i g n i f i c a n t l y d i f f e r e n t than t h a t f rom d i r e c t l y connected impervious areas. For t he c a l i b r a t i o n events, us ing i n i t i a l a b s t r a c t i o n and uni form loss r a t e values presented i n t h e prev ious sec t ion , numerous s imu la t ion runs were made t o determine the q u a n t i t y o f r u n o f f c o n t r i b u t i o n from impervious areas. Resul ts o f these s imula t ions revealed t h a t no runof f from the non -d i rec t l y connected impervious areas appears t o have occurred.

I n i t i a l l y , d i r e c t l y connected impervious areas were i n p u t as c o n t r i b u t i n g 100 percent o f t he r a i n f a l l which f e l l on them t o t he conveyance system. However, even with no c o n t r i b u t i o n from perv ious and i n d i r e c t l y connected impervious areas, the volume o f r u n o f f computed us ing a l l o f t h e r a i n f a l l on d i r e c t l y connected areas exceeded measured volumes. C a l i b r a t i o n was achieved by reducing t h e c o n t r i b u t i o n o f d i r e c t l y connected impervious areas t o 85 percent f o r roadways, driveways, pa rk ing l o t s , e t c . and 80 percent f o r r o o f tops. Th i s s l i g h t l y lower percentage o f c o n t r i b u t i o n from roo f tops takes i n t o account t he e f f e c t o f r o o f ponding.

3.5.3 C a l i b r a t i o n o f Hydrau l ic I n p u t Data

Based on a cursory i nspec t i on o f t h e age and c o n d i t i o n o f t h e conveyance f a c i l i t i e s i n the Cleveland Street 8asin, together w i t h an ana lys i s o f t he a n t i c i p a t e d e f f e c t of losses due t o connections, bends and entrance cond i t ions , "n" values i n t he range from -015 t o ,017 were i n i t i a l l y es t imated f o r t he Cleveland S t r e e t box. However, a comparison o f t he s imulated f lows and water surface e leva t i ons computed using these values t o measured data i n d i c a t e d t h a t t h e ac tua l e f f e c t i v e "n" values were much higher. I n o rder t o o b t a i n c a l i b r a t i o n , va lues i n the range from .020 t o -025 were requi red.

Because these "n" values appeared extremely h igh, they caused some concern about t he accuracy o f t h e f i e l d measurements aga ins t which t h e s imulated r e s u l t s were be ing c a l i b r a t e d . I n order t o asce r ta in whether such values were r e a l i s t i c , t he box c u l v e r t was f i e l d inspected from C la rk Avenue t o Occident Street, a d is tance o f approximately one m i le . In t h i s reach, 18 u t i l i t y c o n f l i c t s ranging from 6 inches t o 18 inches i n diameter were observed. While t h e s ide w a l l s and top o f t he box were found t o be r e l a t i v e l y smooth and i n good cond i t i on , the f l o o r of t he box was observed t o be q u i t e rough i n tex- ture. Some minor f a c t o r s which increased f r i c t i o n w i t h i n t h e c u l v e r t , such as roughness a t cons t ruc t i on j o i n t s , t i e rods extending i n t o t h e box and bar- nacles on the sidewalls i n t i d a l areas were also observed. I n add i t i on , s i l t up t o one f o o t i n depth was found i n t h e area between Westshore and Occident. An ana lys i s made o f t he probable e f f e c t o f t he obs t ruc t i ons i n the box c u l v e r t and t h e roughness o f t h e box f l o o r i n d i c a t e d t h a t , g iven t h e c o n d i t i o n s observed, an e f f e c t i v e "n" value o f -022 was reasonable.

3 .5 .4 Cal i bration Results

Comparisons o f the simulated and measured flows and elevat ions at the gauging site (located at the intersection o f C l eve1 and Street and Clark Avenue) for the February 2nd event are presented in Figures 3-8 and 3-9, respectively. Figures 3-10 and 3-11 present similar comparisons at the same location for the event which occurred on January 20.

As can be observed, the simulated runoff volumes, peak flows and times of concentration ( the point i n time when peak flows occurred) are reasonably close to t h e measured data f o r these events. The apparent differences between simulated and measured results were f e l t t o occur primarily because only t h e major f a c i l i t i e s (generally, 36 inches or larger) i n the system were modeled, t h e uniformity o f rainfall throughout the basin assumed by the model is questionable for the actual event and because o f the limitations o f the model itsel f. Considering these factors, the i nput parameters derived through t h e cal i brati on process were deemed to represent, wi thi n an acceptable degree o f accuracy, the hydrologic and hydraulic conditions existing i n the Clevel and Street Basin and to be suitable for use i n the evaluation of proposed a1 ternati ve sol utions.

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Sect ion 4

ANALYSIS OF SYSTEM ALTERNATIVES

4 . 1 PROBLEM AREAS

Predicated on the h i s t o r i c a l records o f f l o o d i n g i n t h e Cleveland Street Basin and the areas o f most severe f l o o d i n g i den t i f i e d by t h e computer model , f i v e problem areas were es tab l ished as the basis f o r developing proposed a l t e r - n a t i v e system improvements. These f i v e areas were:

OProblem Area No. 1: The area nor th and south o f Cleveland S t r e e t from Azeele t o Kennedy Boulevard between the western boundary o f t h e bas in and Manhattan Avenue.

'Problem Area No. 2: The area w i t h i n the Cleveland S t r e e t Bas in l y i n g south o f Kennedy Boulevard and eas t o f Himes Avenue.

OProblem Area No. 3: The areas j u s t n o r t h and south o f Cleveland Street between Manhattan and Church Avenues.

'Problem Area No. 4: The area w i t h i n t h e Cleveland S t r e e t Basin l y i n g n o r t h o f Kennedy Boulevard and east o f Hirnes Avenue.

OProblem Area No. 5 : The area n o r t h o f problem area No. 1 between Kennedy Boulevard and 1-275 from t h e northward extension o f Occident t o Manhattan Avenue.

F igure 4-1 d i sp lays the approximate l oca t i ons o f these areas.

4 . 2 SYSTEM IMPROVEMENT TYPES AVAILABLE

Four types o f system improvements appeared t o be a v a i l a b l e t o a l l e v i a t e the severe f 1 oodi ng o c c u r r i ng w i t h i n the bas i n. Those considered i n c l uded:

O New conveyance f a c i 1 i t i e s , para1 l e l i ng o r rep lac ing t h e e x i s t ? ng system.

* Detent ion f a c i 1 i ti es.

O A separate o u t f a l l f o r t h e system which serves the Westshore shop- p i n g center and surrounding area.

Improvement o f f l o w cond i t i ons i n the ex i s t i ng system by reducing f r i c t i o n losses and e l i m i n a t i n g obs t ruc t ions .

O f these, new conveyance f a c i l i t i e s and de ten t i on f a c i l i t i e s a re t h e on l y improvement types which have the p o t e n t i a l t o e f f e c t i v e l y el im ina te f l o o d i n g throughout t h e basin du r ing a design storm event. However, the separate o u t f a l l f o r Westshore and improvement o f t h e f l ow cond i t i ons in the e x i s t i n g system both prov ide s i g n i f i c a n t r e l i e f w i t h r e l a t i v e l y minor cost . For that

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reason, a se r ies of a l t e r n a t i v e so lu t i ons u t i l i z i n g combinations o f t h e f o u r improvement types a v a i l a b l e were i d e n t i f i e d , analyzed w i t h the computer model and assessed i n terms of water qua1 i t y impact and cost .

4.3 ALTERNATIVES CONSIOERED

Al together , twelve system improvement a l t e r n a t i v e s were analyzed. These a l t e r n a t i v e s were developed b y app ly ing the f o u r improvement types discussed above t o t he f i v e problem areas which had been i d e n t i f i e d . They represent a spectrum o f possi b l e so l u t i o n s which range from minor improvements that wi 11 reduce, b u t n o t e l im ina te , f l o o d i n g i n any problem area t o major improvements needed t o e l im ina te a l 1 f l o o d i n g w i t h i n the Cleveland S t r e e t Basin du r ing a design storm event .

A l t e r n a t i v e No. 1, shown i n F igure 4-2, cons i s t s of a complete new c losed condu i t system pa ra l 1 e l i ng t h e e x i s t i n g system. Th is a1 t e r n a t i v e would e l im ina te f l o o d i n g throughout the basin, b u t was the m o s t c o s t l y a l t e r n a t i v e considered.

A l t e r n a t i v e No. 2, presented i n F igure 4-3, would a l s o e l im ina te f l o o d i n g throughout t h e basin. Th i s s o l u t i o n i s comprised of a system o f de ten t i on basins w i t h secondary, l o c a l i z e d p i p e improvements.

A l t e r n a t i v e No. 3 was analyzed t o determine the b e n e f i t t h a t cou ld be der ived f r o m improving f l o w cond i t i ons i n t h e e x i s t i n g box c u l v e r t i n Cleveland Street by l i n i n g t h e f l o o r of the box and e l i m i n a t i n g obs t ruc t ions . I n t h i s a l t e r n a t i v e , no o the r improvements were considered. The computer model run o f A l t e r n a t i v e No. 3 i n d i c a t e d t h a t o n l y minor reduc t ion i n f l o o d i n g would r e s u l t f r o m implementat ion o f t h i s improvement alone.

A l t e r n a t i v e No. 4, shown i n F igure 4-4, combined improvement o f t he Cleveland S t r e e t box f l ow cond i t i ons w i t h the cons t ruc t i on o f a new, separate o u t f a l l f o r t h e Westshore area. Th is a1 t e r n a t i ve woul d e l i r n i nate f l oodi ng i n Problem Area 1, bu t would have 1 i ttl e impact e l sewhere i n t h e bas i n.

A1 t e r n a t i v e No. 5, presented i n F igure 4-5, inc ludes the new Westshore o u t f a l l , improvement o f t h e Cleveland S t r e e t box f l o w cond i t i ons and de ten t i on f a c i l i t i e s w i t h minor p ipe improvements eas t o f Himes Avenue. This a l t e rna - t i v e would e l i m i n a t e f l o o d i n g i n Problem Areas 1, 2 and 4.

A 1 t e r n a t i v e No. 6 is dep ic ted i n F igure 4-6. I t i s s i m i l a r t o A l t e r n a t i v e No. 5 except t h a t no improvements are prov ided i n t he area nor th o f Kennedy Boulevard, eas t o f H i mes Avenue. These improvements woul d e l i r n i nate f 1 oodi ng i n Problem Areas 1 and 2.

A l t e r n a t i v e No. 7, shown i n F igure 4-7, inc luded a new Westshore o u t f a l l , improvement o f f 1 ow cond i t i ons i n t h e e x i s t i ng box c u l v e r t and d e t e n t i on f a c l i t i e s i n the area south o f Kennedy Boulevard, eas t o f Himes Avenue and i n t h e v i c i n i t y o f Cleveland Street and Grady Avenue. Th is a l t e r n a t i v e would e l irni na te f l o o d i n g i n Problem Areas 1, 2 and 3 .

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A l t e r n a t i v e No. 8, shown i n F igure 4-8, a l so would e l im ina te f l o o d i n g i n Problem Areas 1, 2 and 3. Th is a l t e r n a t i v e c o n s i s t s o f a new Westshore out - fa1 1 , improvement o f f 1 ow cond i t i ons i n the C l evel and S t r e e t box, de ten t ion f a c i l i t i e s south o f Kennedy Boulevard, eas t o f Hirnes Avenue and a new box c u l v e r t , para1 1 e l i ng the Cl evel and S t r e e t box a1 ong Azeel e S t ree t from C la rk Avenue w e s t t o t he e x i s t i n g o u t f a l l .

A l t e r n a t i v e No. 9 is presented i n F igure 4-9. The improvements considered i n t h i s a l t e r n a t i v e inc lude the new Westshore o u t f a l l , improved cond i t ions i n the Cleveland S t r e e t box and de ten t i on f a c i 1 i t i e s no r th and south o f Kennedy Boulevard, eas t o f Hirnes Avenue, and i n the v i c i n i t y o f t h e i n t e r s e c t i o n o f Cl eve l and S t r e e t and Grady Avenue. Imp1 ementation of t h i s a l t e r n a t i ve would el i m i nate f 1 oodi ng i n a1 1 Probl em Areas except Problem Area 5.

A l t e r n a t i v e No. 10, shown i n F igure 4-10, i nc ludes a1 1 the improvements i n A l t e r n a t i v e No. 9 except t he new Westshore o u t f a l l . The r e s u l t s o f the computer model f o r t h i s a l t e r n a t i v e i n d i c a t e t h a t , w i thou t t h e Westshore o u t f a l l , f l o o d i n g w i l l occur i n Problem Area 1 as we1 l as minor f l ood ing i n Problem Area 3.

A l t e r n a t i v e No. 11 i s i d e n t i c a l t o A l t e r n a t i v e No. 10 w i t h the except ion t h a t i t does n o t i nc lude improving f l o w cond i t i ons i n t he Cleveland S t ree t box c u l v e r t . With t h i s a1 t e r n a t i v e , s i g n i f i c a n t f l o o d i n g would occur i n Problem Areas 1 and 3. Th i s a l t e r n a t i v e demonstrates t h a t the f l o o d i n g i n Problem Area 1 can on l y be solved e i t h e r by p rov id ing storage i n t h e immediate v i c i n i t y o r by conveyance improvements t o t h e Cleveland Street box and t h e separate Westshore o u t f a l l .

A? t e r n a t i ve No. 12 , shown i n F igure 4-11, i nc ludes t h e new Westshore o u t f a l l , improved f l o w cond i t i ons i n t h e e x i s t i n g Cleveland S t r e e t box culvert and d e t e n t i on f a c i 1 i ti e s n o r t h and south of Kennedy Boulevard, eas t o f Himes Avenue, i n t h e v i c i n i t y o f t he i n t e r s e c t i o n o f Cleveland Street and Grady Avenue and i n the Westshore area. Thi s a1 t e r n a t i ve you1 d e l i m i na te f 1 oodi rig i n a l l f i v e problem areas.

4.4 MODELING OF CONTROL ALTERNATIVES

A1 1 twelve a l t e r n a t i v e s c i t e d i n Sec t i on 4.3 were analyzed w i t h t h e computer model. I n p u t parameters used du r ing these model runs were those es tab l ished du r ing c a l i b r a t i o n . Each a1 t e r n a t i v e was modeled using the design storm ( f i v e year recurrence frequency) event.

The c r i t e r i a adopted f o r eva lua t i ng t h e e f fec t iveness o f each a l t e r n a t i v e i n e l i m i n a t i n g f l o o d i n g was the volume o f over f low f r o m nodes w i t h i n the system du r ing surcharge and t h e du ra t i on o f surcharge. The maximum acceptable volume o f over f low a t any p o i n t i n t h e system was one ac re - foo t o f stormwater. I n nearly a l l areas the volume o f over f low was maintained a t less than 5,000 cub ic f e e t and over f low dura t ions were general l y l ess than t e n minutes.

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4 .5 WATER QUALITY ASSESSMENT

4 . 5 . 1 Peak Flows

Table 4-1 l i s t s and summarizes t h e var ious a l t e r n a t i v e s , s t a r t i n g w i t h A l t e r n a t i v e 0, which i s t he "no ac t i on " p lan. The table shows the the computed peak ou t f l ow rates and the respect ive percentages o f t he "base" or "no ac t ion" f i g u r e s . Also, t he t a b l e ind ica tes which p r i o r i t y areas (1 through 5) a re pred ic ted t o undergo s i g n i f i c a n t f l o o d c o n t r o l improvement under each a1 t e r n a t i v e .

Since the r a i n f a l l and land use c h a r a c t e r i s t i c s are the same i n a l l cases, t he t o t a l volume o f water l eav ing the system f o r t he var ious a1 t e r n a t i v e s should be very s i m i l a r . This volume i s approximately 5.9 m i l l i o n cubic f e e t du r ing the design storm event.

4.5.2 De ten t i on Times and P o l l u t a n t Load Reductions

The po l l u t a n t load r e s u l t i n g from each a l t e r n a t i v e i s a f f e c t e d ( t o some degree) by t he ex teh t of de ten t i on storage provided. The a l t e r n a t i v e s d i f f e r i n t h e s i ze , l o c a t i o n and number o f de ten t i on bas ins. I n a t y p i c a l subarea, t he peak f l o w i s i n t he range o f 100 t o 200 cubic f e e t per second ( c f s ) . Most de ten t ion basins have volumes ranging from h a l f a m i 11 i o n t o a m i 11 i o n cubic f e e t . Thus, t he de tent ion t imes are est imated t o be between 1 and 4 hours.

The stormwater study, e n t i t l e d "Study and Assessment o f t he Capabi 1 i t i e s and Cost o f Technology of Contro l o f P o l l u t a n t Discharges from Urban Runoff", conducted by the Nat ional Commission on Water Q u a l i t y i n 1975 repo r t s p o l l u t a n t l oad reduct ions f o r var ious de tent ion t imes. For t h e range o f 1 - 4 hours, a 30 percent reduc t ion i n BOD suspended s o l i d s , n i t rogen and phosporus appears reasonable.

Since A1 t e r n a t i v e 2 prov ides de ten t i on ponds throughout t h e Cl eve1 and S t r e e t Basin, a 30 percent p o l l u t a n t load reduct ion i s est imated r e l a t i v e t o t h e "no ac t ion" cond i t ion . A l t e r n a t i v e s 5, 9 , 10 and 11 each prov ide 5 o r 6 de ten t i on basins, thus p rov id ing de ten t i on f o r approximately 50 percent o f t he flow. For these, a reduc t ion o f 15 percent (i . e. , ha1 f o f the 30 percent above) i s est imated. A l t e r n a t i v e s 6, 7 and 8 each prov ide 3 o r 4 de ten t i on basins, o r de ten t ion o f approximately one- th i r d o f t he f low. An o v e r a l l removal rate o f 10 percent i s est imated f o r t h e s e a1 t e rna t i ves . A1 t e r n a t i v e 12 prov ides de ten t i on f o r approximately 60 percent o f the f l o w and would the re fo re r e s u l t i n an est imated removal rate o f 18 percent. Table 4-2 d isp lays the est imated r u n o f f pol 1 u t a n t 1 oads f o r t he var ious a1 t e r n a t i v e s considered.

4.5.3 Shock Loadi ng

The a1 t e r n a t i v e s n o t on ly d i f f e r i n t h e i r t o t a l p o l l u t a n t loads depending on t h e use o f de ten t ion , b u t a l s o i n t h e d i s t r i b u t i o n o f the p o l l u t a n t load over t he du ra t i on o f t h e storm. General ly , t he h igher t he peak f l o w and peak load ing ra te , the more adverse would be t h e impact on the r e c e i v i n g lagoon.

The degree o f usage o f in-system de ten t i on storage has a great impact on peak f low, as can be seen by comparing the peak f lows o f two o f t he most e f f e c t i v e a1 t e r n a t i ves i n terms o f reduced f 1 oodi ng:

TABLE 4-1

COMPARISON OF COMPUTED PEAK FLOWS AND FLOODING IMPROVEMENTS FOR VARIOUS ALTERNATIVES DURING THE DESIGN STORM^

ALTERNATIVE SIGNIFICANT IMPROVEMENTS

COMPUTED PEAK RATE I N PROBLEM AREAS

Flow % o f No. D e s c r i p t i o n ( c f s ) Base 1 2 3 4 5

0 Base c o n d i t i o n (No a c t i o n ) 567 100

1 Closed condu i t system 1 ,615 285 X X X K

2 Primary storage Improvements 526 93 X X X X X w i t h some p i p e improvements

3 Improved f l o w condi ti ons f o r 652 115 Cleveland Street box c u l v e r t

4 Improved f l o w c o n d i t i o n s f o r 906 160 X Cleveland Street box culvert (combi ned) and separa te o u t f a l l for Westshore a r e a

5 Same as A1 t e r n a t i v e 4 , p lus 907 160 X X X i rnprovements f rom Al$ernati ve (combined) 2 1 ocated e a s t o f Hirnes

6 Same as A1 t e r n a t i v e 5 , plus 906 160 X X improvements south o f Kennedy Boulevard

7 Same as A l t e r n a t i v e 6 p l u s 906 160 H X K storage a t Grady and Cleveland (combined) from A l t e r n a t i v e 2

8 Same as A l t e r n a t i v e 6 plus 1,067 188 X X p a r a l l e l o u t f a l l a long Azeele (combined) S t ree t ( f rom Clark Street t o e x i s t i n g o u t f a l l )

9 Same as A l t e r n a t i v e 5 p l u s 849 150 X X X K storage a t Grady and Cleveland f rom A1 ternat ive 2

TABLE 4-1 (Continued)

ALTERNATIVE SIGNIFICANT IMPROVEMENTS

COMPUTED PEAK RATE I N PROBLEM AREAS

Fl ow % o f No. Description (c f s) Base 1 2 3 4 5

10 Same as Al te rna t i ve 9, b u t 652 115 ( x l b ( X ) (X) (X) without Westshore outfall

11 Same as A1 ternati ve 10, but 570 10 1 without improvements to

(XI (XI (XI (XI

Cleveland Street box flow c o n d i t i o n s

12 Same as A1 t e r n a t i v e 9 plus detent ion storage i n West- shore area.

X X X X X

a Design storm i s a once i n 5-year frequency, 1.5 hour dura t i on event , w i t h t o t a l rainfall of 3 . 3 i n c h e s .

Parentheses i n d i c a t e some improvements but n o t as significant as those frornprevious a1 te rna t i ves.

ESTIMATED RUNOFF POLLUTANT LOADS FROM ! THE CLEVELAND STREET BASIN FOR THE VARIOUS

ALTERNATIVES CONSIDERED

YEARLY RUNOFF POLLUTANT LOADS, LBS.

ALTERNATIVE SUSPENDED BOD5 TOTAL TOTAL NUMBER SOLIDS NITROGEN PHOSPHORUS

A l t e r n a t i v e 1: closed condu i t systems (peak f l o w 285 percent o f "base" peak)

O A l t e r n a t i v e 2: pr imary storage improvements w i t h some p ipe improvements (peak f l o w 93 percent o f "base" peak)

I f o t h e r f a c t o r s ( e . g . , c o s t ) were equal, A l t e r n a t i v e 2 would be p re fe rab le t o 1 from a water qual i t y "shock loading" s tandpoint .

A l t e r n a t i v e s 5 through 9 may be grouped i n a "moderately e f f e c t i v e " group, s ince they a l l a l l e v i a t e f l o o d i n g i n some problem areas, bu t n o t i n a l l . I n t h i s group, the range o f percentage o f peak f l o w t o the base i s f a i r l y narrow, 150 t o 188. Thus, the impact o f these a l t e r n a t i v e s l i e s between t h a t o f a1 t e r n a t i ves 1 and 2 , discussed above.

A l t e r n a t i v e 12 e f f e c t i v e l y a l l e v i a t e s f l o o d i n g i n the problem areas. The percentage o f peak f l o w t o t h e base i n 146. Thus, t he shock l oad impact of t h i s a1 t e r n a t i ve i s sl i g h t l y b e t t e r than the "moderately e f f e c t i v e " group.

A l t e r n a t i v e s 3, 10 and 11 have a very moderate impact i n te rms o f shock loading, j u s t s l i g h t l y greater than t h a t f o r A1 t e r n a t i v e 2. However, these t h r e e a l t e r n a t i v e s o f f e r less improvement i n f lood ing .

F o r t he a l t e r n a t i v e s which inc lude de ten t i on ponds, a reduc t ion i n t o t a l p o l l u t a n t loads can be expected and should p a r t i a l l y o f f s e t any increase i n t he peak p o l l u t a n t load ing r a t e t o Neptune Lagoon. Also, because ambient water q u a l i t y i n t h e e x i s t i n g lagoon appears t o be poor, any s h o r t term reduct ions i n s a l i n i t y due t o increased peak f l ow ra tes should no t degrade e x i s t i n g water qual i t y .

4 . 5 . 4 Summary o f Water Q u a l i t y Eva lua t ion

From a w a t e r q u a l i t y s tandpoint , A l t e r n a t i v e 2 would be preferred. I n a d d i t i o n t o a l l e v i a t i n g f l o o d i n g i n a l l p r i o r i t y areas, i t would reduce t he peak ou t f l ow r a t e from t h a t i n t he "no ac t i on " plan. I t would a l s o reduce p o l l u t a n t load ing by approximately 30 percent f r o m the "no ac t i on " p lan. A l t e r n a t i v e 2 would be favored i f t h e necessary land f o r a l l t h e de ten t i on basins could be obta ined a t a reasonable cost .

A l t e r n a t i v e s 5 through 1 2 i n v o l v e de ten t i on basins. O f these, 10 and 11 r e s u l t i n ve ry moderate peak f l o w increases over the "no ac t ion" a l t e r n a t i v e , b u t they do n o t r e s u l t i n as much improvement i n f l o o d reduc t i on as others i n t h e group. O f t h e o the r so lu t i ons considered, a l t e r n a t i v e 12 has t he smal lest increase i n peak f l o w and f l o o d c o n t r o l b e n e f i t s t o t he l a r g e s t number o f p r i o r i t y areas. Its reduc t i on i n p o l l u t a n t l oad r e l a t i v e t o the "no ac t ion" p l a n i s es t imated a t 18 percent . A l t e r n a t i v e 12 would be a good second choice a f t e r A l t e r n a t i v e 2 i n te rms o f water q u a l i t y impact.

4.6 EVALUATION OF ALTERNATIVES

The eva lua t i on o f t he twelve a1 t e r n a t i v e s considered and s e l e c t i o n o f the p re fe r red a1 t e r n a t i ve were based on th ree major fac tors ; cos t , water qual i ty impact and performance.

Order o f magnitude c o s t est imates were prepared f o r each a1 t e r n a t i v e . These e s t i m a t e s inc luded a n t i c i p a t e d r igh t -o f -way costs based on c u r r e n t land value guide1 i nes prov ided by t h e C i t y o f Tampa Right-of-way D i v i s i o n , p ro jec ted costs f o r the i n s t a l l a t i o n o f new f a c i l i t i e s and, where appropr iate, t he cos t o f r e s t o r i n g roadway f a c i l i t i e s which would be a f fec ted by the cons t ruc t i on o f proposed drainage improvements. These order o f magnitude est imates are summarized i n Table 4-3.

The comparative water q u a l i t y impacts o f the twelve a l t e r n a t i v e s considered were as discussed i n Sect ion 4.5.

The bas is used f o r eva lua t ing the performance o f each a l t e r n a t i v e was i t s impact on f l ood ing i n each o f t he f i v e problem areas i d e n t i f i e d . These impacts were discussed i n Sect ion 4.3 and are summarized, together w i t h costs and water qual i t y impacts i n the mat r i x presented i n Tab1 e 4-4.

A l l twelve a l t e r n a t i v e s analyzed were considered t o be f e a s i b l e f rom t h e s tandpo in t o f cons t ruc tab i 'I i ty . With t h e except ion o f A 1 t e r n a t i ve No. 3 (improvement o f f l o w cond i t i ons i n t he Cleveland Street box c u l v e r t ) , t he implementation o f each a l t e r n a t i v e necessar i l y invo lves some negat ive impacts. These range from d i s r u p t i o n o f t r a f f i c dur ing the i n s t a l l a t i o n o f new conveyance f a c i l i t i e s t o the p o s s i b i l i t y o f condemnation and r e l o c a t i o n i n o rder t o ob ta in and cons t ruc t stormwater detent ion s i t e s . Since the eva lua t i on o f these f a c t o r s is n o t s imply a mat ter o f engineer ing judgement, i t i s recommended t h a t t he we igh t g iven t o these f a c t o r s be determined by o f f i c i a l s o f t h e C i t y o f Tampa w i t h whatever techn ica l i n p u t they may r e q u i r e from PBS&J.

TABLE 4-3

SUMMARY OF ALTERNATE IMPROVEMENT ESTIMATES

RETENTION ALT. PIPING LAND POND BOX TOTAL NO. COST ACQUIS IT ION COST CONSTRUCTION IMPROVEMENT COST

NOTE: A l l est imates are based on May, 1983 p r i c e s .

TABLE 4-4

SUMMARY OF EVALUATION CRITERIA

A1 ternative Estimated Number Costs

Water Qua1 i ty Performance Impacts (Problem Areas

(at outfall) Eliminated)

Increases short term loading A1 1

30% reduction i n pollutant loading All

No impact None. Minor reduction in 1 and 3

Increases short term loading 1

15% reduction in pollutant loading 1, 2 & 4

10% reduction i n pollutant loading 1 & 2

10% reduction i n pollutant loading 1, 2 & 3

10% reduction i n pollutant loading 1, 2 & 3

15% reduction in pollutant loading 1, 2, 3 & 4

15% reduction in pollutant loading 2 & 4 minor flooding i n 3

15% reduction i n pollutaftt loading 2 & 4

18% reduction in pollutant loading All

SECTION 5

CONCLUSIONS AND RECOMMENDATIONS

5.1 SELECTION OF THE PREFERRED ALTERNATIVE

As can be seen from a rev iew o f Table 4-4, only th ree of t he schemes considered, A 1 t e r n a t i v e s 1, 2 and 12 , p rov ide re1 i e f from f l o o d i n g i n a1 1 f i v e problem areas. O f these, A l t e r n a t i v e No. 1 was by f a r t he most expensive w i t h an est imated c o s t o f $21,500,000, almost tw i ce as c o s t l y as the nex t h ighes t so lu t i on . I n add i t i on , A1 t e r n a t i v e No. 1 r e s u l t s i n the most adverse wate r q u a l i t y impacts o f any of t h e candidate so lu t ions . A l t e r n a t i v e No. 2 i s equa l l y e f f e c t i v e i n e l i m i n a t i n g e x i s t i n g f l o o d i n g problems, and has the most favorab le impact on water q u a l i t y . It does no t , however, u t i l i z e two improvement types (improvement o f f l o w cond i t ions i n t h e Cleveland Street box and a separate o u t f a l l f o r Westshore) which prov ide s i g n i f i c a n t b e n e f i t s a t re1 a t i v e l y 1 ow cos t .

A l t e r n a t i v e No. 12, through i n c l u s i o n o f these improvement types, prov ides r e l i e f f r o m f l o o d i n g i n a l l f i v e problem areas a t the l e a s t cost . Because t h i s s o l u t i o n inc ludes the new Westshore o u t f a l l , the water q u a l i t y impact r e s u l t i n g f r o m i t s implementation would no t be q u i t e as p o s i t i v e as t h a t f o r A l t e r n a t i v e No. 2, bu t would compare favorab ly w i t h t h e e x i s t i n g system. This a l t e r n a t i v e a l s o lends i t s e l f w e l l t o a phased program f o r implementation. For these reasons, A l t e r n a t i v e No. 12 i s recommended a5 the p r e f e r r e d a l t e r n a t i v e f o r s o l u t i o n o f t h e e x i s t i n g f l o o d i n g problems i n the Cleveland S t r e e t Basin. The phys ica l improvements associated w i t h the p r e f e r r e d a l t e r n a t i v e are presented i n Figures 5-1W and 5-IE.

5.2 DER RESPONSE

A subsequent meeting w i t h t h e DER was h e l d t o d iscuss p e r m i t t i n g requirements, poss ib le c o n s t r a i n t s and o v e r a l l a c c e p t a b i l i t y of the p re fe r red s o l u t i o n . Pe r t i nen t p o i n t s made du r ing t h i s meeting are i n d i c a t e d be1 ow.

O Regardless which a l t e r n a t i v e i s f i n a l l y s e l e c t e d t h e t o t a l volume o f runo f f d r a i n i n g t o Old Tampa Bay w i l l be t h e same f o r a l l a l t e r n a t i v e s s ince no change i n l and use i s expected nor t o t a l r e t e n t i o n proposed w i t h i n the basin.

* A1 t e r n a t i v e s t h a t i nc l ude de ten t i on f a c i 1 i ti es would be preferred over a l t e r n a t i v e s t h a t do n o t i nc lude de ten t i on f a c i l i t i e s .

O The DER does n o t have j u r i s d i c t i o n over the conveyance systems w i t h i n t h e basin. T h e i r j u r i s d i c t i o n and pr imary concern i s a t t he o u t f a l l , Neptune Lagoon.

I ;I I CYPREBB I--I I I ST- I I - u L

NORTH

POST, BUCKLEY, SCHUH & JERNIGAN, INC. CONSULTING ENGINEERS 8 PLANNERS

CLEVELAND STREET BASIN (WEST) u TAMP*, FLORIDA

PREFERRED AbTERWATtVE IMPROVEMENTS DEPARTMENT OF PUBLIC WORKS 4

It was indicated to DER t h a t where economically practical the preferred alternative does utilize detention facilities to alleviate flooding and reduce total pollutant loads to Neptune Lagoon.

O The structural improvements at the existing outfall (Westshore relief line) would require a joint Dredge and Fill and Notice of Stormwater Discharge permit. The DER d i d not seem overly concerned with t h i s improvement. It was indicated to them t ha t although the "shock load" would be increased the total pol lutant load would be decreased because the preferred alternative does include numerous detention facilities. A suggestion that the DER made was to create a shallow natural ,wetland at the new outfall. This could be accomplished by terminating t h e new outfall just south o f Azeele Street and excavating a shallow area that could be planted with wetland vegetation to connect the new outfall to Neptune Lagoon.

The preferred alternative improvements does not exempt development or redevelopment projects from meeting DE8 Notice of Stormwater Discharge requirements.

O The water qua1 ity evaluation was sufficient to "weigh" the potential effects of t h e various improvements.

In summary, the DER was pleased to find that the preferred alternative did include numerous detention facilities throughout the basin and pre1irnina.r~ indications were that,the improvements proposed in the preferred alternative would be permi t a b l e activities.

5.3 FINANICAL REQUIREMENTS AND PHASING

A four s t e p phasing plan for implementation of t h e preferred alternative, indicating t h e proposed improvements and associated costs f o r each phase, is presented in Table 5-1.

Land acquisition represents a substantial portion of the overall cost to implement the plan and will be a critical element in t h e schedule for completing the improvement program. It is therefore recommended that design o f the system, in s u f f i c i e n t detail to clearly delineate the areas required for detention, and actual land acquisition be budgeted and initiated as the first step i n t h e process. No inflation factor has been included i n the cost estimates presented in this report and it is reasonable to assume t h a t early acquisition will also result i n lower l a n d costs.

REPZO: F

TABLE 5-1

PROPOSED PHASING PLAN

PHASE NO. IMPROVEMENTS RIGHT-OF-WAY CONSTRUCTTON TOTALS REMARKS

1 Improve f l o w cond i t i ons i n t h e $ 231,000 $1,269,000 $1,500,000 Re l ieves f l o o d i n g i n p r o b l e m e x i s t i n g Cleveland Street box area 1. and cons t ruc t a new o u t f a l l f o r t h e Westshore area.

2 Construct de ten t i on f a c i l i t i e s $1,977,000 $ 523,000 $2,600,000 Re1 ieves f 1 oodi ng i n problem area and associated p ipe improvements 2. Conf igura t ion o f the system i n the area e a s t o f Himes Ave., w i l l be the same as A l t e r n a t i v e south o f Kennedy Blvd. No. 6 (See F igu re 4-6)

3 I n s t a l l the proposed de ten t i on $3,100,000 $1,200,000 $4,300,000 Rel ieves f l o o d i n g i n p r o b l e m a r e a f a c i l i t i e s and l o c a l p ipe i m - 4. System improvements completed provements i n t h e area e a s t o f through t h i s phase w i l l be the same Himes Ave., n o r t h of Kennedy as those shown f o r A l t e r n a t i v e No. Blvd. 9. (See F igure 4-9)

4 I n s t a l l t h e proposed de ten t i on $ 626,000 $1,284,000 $1,910,000 Completes improvements f a c i l i t i e s and p i p i n g i n t h e Westshore area between Kennedy Blvd. and 1-275.

APPENDIX A

Minor Losses

OPEN CHANNEL HYDRAULICS

DEVEMPYEKT OF VmFORII FLOW A N D ITB F O R M U M 101

tor n between 0.011 nnd 0.040. For practical purposes, the followhg spproximate forms of Eq. (59) are generally suggested for use:

y = 1.5 &n for R < 1.0 m (5-10) y=1.3&n f o r R > I . O m (5-11)

6-7. Determination of Manning's Roughness Coefficient. In applying the Manning formula or. the G. K. formula, the greatest difficulty lies in the determination of the roughness coefficient n; tor there is no exact method of selecting the n value. At the present stage of knowledge, to select a value of n nctually means to estimate the resistance to flow in a given channel, which is really a matter of intangibles. To veteran engineers, this mesns the exercise of sound engineering judgment and experience; for beginners, it can be no more than a guess, and diiierent individuals mill obtain different results.

In order to give guidance in the proper determination of the roughness coefficient, four general approaches nill be discussed; namely, (1) to understand,the factors tbat affect the value of n and thus to acquire s basic knowledge of the problem and narrow the wide range of guesswork, (2) to consult a table of typical n values for channels of vsrious types, (3) ta examine and become acquainted with the sppenrance of some typical channels whose roughness coefficients are known, and (4) to determine the value of n by an analytical procedure based on the theoreti- cal velocity distribution in the channel cross section and on the data of either velocity or roughness measurement. The 6rst three approaches 'SPiU be given in the next three srtjcles, and the fourth approach will be taken up in Art. 8-7.

6-8. Factors Affecting Manning's Rougbness Coe5cient It is not uncommon for engineers to think of a channel ns having a single value of n for aU occasions. In reality, the vdue of n is highly variable and depends on a number of factors. In selecting a proper value of n lor variolls design conditions, a basic knmv1edge of these factors should be found very useful. The factors that exert fhe greatest influence upon the coefficient of roughness in both arti6cial and natural channels are therefore described below. I t should be noted tbat these factors are to a certain extent interdependent; hence discussion about one factor may be repeated in connection with another.

A . Surjuce Roughness. The surface roughness is represented by the 6ize and shape of the grains ol the mnterial forming the wetted perimeter Bnd producing a retording effect on the flow. This is olten considered the only f ~ c t o r in selecting n roughness coefficient, but it is actually just one 01 several major factors. Generally speaking, fine grains result

a relatively low value of n and coarse grains, in a high vnlue of n. In alluvial streams where the haterial is fine in grnin, such as snnd,

The U.S. Soil Consemation Service has made studies on flow clf water m srnnU shallow channels protected by vegetative linings (Chap. 7, Set. C). It was found that n values for these channels varied with the s h ~ p e and cross section of the'channel, the slope of the channel bed, and the depth of flow. Comparing two channels, a1 other factors being equal, the lesser average depth gives the higher n value, owing to a larger proportion of affected vegetation. Thus, a triangular channel has a higher n value than a trapezoidal channel, and a wide channel has a lower n value than a narrow channel. A flow of sufficient depth tends to bend over and submerge the vegetation and to produce low n values. A steep slope causes greater velocity, greater flattening of the vegetation, and low n values.

The effect 01 vegetation on flood plains will be discussed later in item H. C. Channel Irreg ularily. Channel tregulnrity comprises irregulnrities

in wetted perimeter nnd variations in cross section, size, nnd shnpe along the chnnnel Iength. In natural channels, such irregularitiea are usually introduced by the presence of sand bara, sand waves, ridges and depre* sions, and holes and humps on the channel bed. These irregularities dehitely introduce roughness in addition t o that caused by surface roughness and other factors. Generally spenking, s gradual and uniform chnnge in cross section, size, and shape will not appreciably &affect the value of n, but abrupt changes or alternation of small and hrge eections necessitates the use of a large value of n. In this case, the inereme in n may be 0.005 or more. Changes that cause sinuoue flow from side to

'i side of the channel will'produce the same effect. 0. Chunnel Alignment. Smooth curvnture with large radius dl give

a relatively low value of n, whereas sharp curvature with severe meander- b g will increase n. On the basis of flume tests, Scobey [231 suggested that the value of n be increased 0.001 for each 20 degrees of curvature in 100 ft of channel. Although it is doubtful whether curvature ever increases n more than 0.002 or 0.003, its effect sbouId not be ignored, for curvature may induce the ~ccumulntion of drift and thus indirectly bcrease the value of n. Genernlly speaking, the increase of roughness

unlined channels carrying water at low velocities is negligible. An bcrease of 0.002 in n vnlue would constitute nu ndequate allownnce for curve losses in most flumes contnining pronounced curvntures, whether built of concrete or other materiala. The meandering of natural stresms, however, may increase the n vnlue ns high as 30%.

Em ailling and Scouring. Generally speaking, silting may chenge 8

irregular channal into a cornpnrntively unilorm one nnddecrew n, whereas scouring may do the revere9 end increase n. However, tbe dominant effect of silting will depend on the nsture of the material deposited. Uneven deposits auch WJ ssnd bsn and mnd wavea are

104 Uh'lFORM FLOW

chnnncl irregulnrjties nnd will jncreasc the roughness. The amount and uniformity 01 scouring will depend on the mnterinl forming the wetted perimeter. Thus, a sandy or gravelly bed wiH be eroded more uniformly than a clay bed. The deposibion of silt eroded from the uplands wiU tend to even out the irregularities in a channel dredged through clny. The energy used in eroding nnd carrying the mnterinl in suspension or rolling it nlong the bed will also increase the n value. The eflect of scouring is not significant as long as the erosion on channel bed caused by high velocities is progressjng evenly and uniformly.

F. Obslruclion. The presence of log jams, bridge piers, and the like tends t o increase n. The amount of increase depends on tbe nature of the bbstructions, their size, shape, number, and distribution. G. Size a n d Shape of Channel. There is no definite evidence about

the size and shape of a chnnnel as an important factor affecting the value of n. An increase in hydraulic radius may either increase or decrease n, depending on the condition oi the channel (Fig. 5-4).

H . Slagc and Discharge. The n value in most streams decreases with increase in stnge and in discharge. Wben the water is shallow, the irregularities 01 tbe channel bottom are exposed and their effects become pronounced. However, the n value may be large at high stages if the banks are rough and grassy.

When the discharge is too high, the stream may overflow its banks and a portion of the £ionn will bc along the flood plain. The n value of the Aood plains is generally larger than that of the channel proper, and its magnitude depends on the surface condition or vegetation. If tbe bed and banks of a chnnnel are equally smooth and regular and tbe bottom slope is uniform, t he value of n mag remain almost the same at all stages; so a constant n is usually assumed in the 0om computation. This happens mostly in artificial channels. On flood plains the value of n usually varies with the stage of submergence of the vegetation at low stages. This can be seen, for example, from Table 3 4 , which shows the n values ior various flood stages according to the t ~ p e of cover and depth

Depth of water, f t

Under 1 l t o 2 2to3 3 h 4 Over 4

Channel seclion

0.03 0.03 G . 03 0.03 0.03

Flood-plain cover

Carn

0.06 0 . 0 6 0.07 0.07 0 .06

Pmture

0.05 0 . 0 5 0 .04 0 . 0 4 0.04

B m b and

0.12 0.11 0.10 0.09 0.08

hfoador

0.10 0.08 0.07 0 .06 0 . 0 5

Smell

0 .10 0 . 0 8 0 . 0 8 0.07 0.06

of ioundntion, as observed in the Nishnabotna River, Iowa, for the average growing season [24]. I t should be noted, however, that vegetation bas a marked effect only up to a certain stage and that the roughness coefficient can be considered to remain constant lor practicaI purposes in dcterrnining overbank flood discharges.

Mirrislippi River between Memphi and Fulion, Tennersee

o U.S. Geo~ogicol Suruey doia a U.S. Cbrpr a! Enginter r dola

-Bank full siage 31 [I

n value

n uolue

Irrawaddy River ot Soiktho,Burrn~

E p 20 O 0.030 a035 0.040 a04 5

n volue

FIG. 5-4. Variations of the n value qi'ith the mean stage or depth. \.

Curves of n value versus stage (Fig. 5-4) in streams have been given by Lane 1251, shoving how value of n vnries with stnge in threg large river channels. For the roughness of large canals, a study in connection 'with the design of the P nama Canal n-as made by Meyers and Schultz [26].' The two most im j 0rtm-i~ conclusions reached from this study were (1) that the n value for a river channel is least when the stage is at or Bornerhat shove normal bankfull stage, and tends to incrense for both

' A table of n v ~ l u e s for eleven large channels st the most efficient depths and the curnee showing the variaLions of n value with hydreulic rac!ius in cigbt river cbaonels

given in this relerence.

106 GXIFORII FLOW

higher and lower stages; and (2) thnt the banklull n vnlues do not vary greatly lor ::;~er~ and canals in djffercnt kinds of material nnd in \r-jdels separ~~ted '7kr;:::iirn~.

For circujar conduits, Camp [27,28] was able t o ahow thnt the n value for a conduit flowing partially full is greater than that lor a lull conduit. Using measurements on clean sewer pipe and drain tile, both clay and concrete, from 4 to 12 in. in size, he found an increase of nbout 24% in the TL value :!t tbe half-depth (Fig. 6-51.' The n value for the pipe flo\vbg full was round to vary from 0.0095 to 0.011. Taking an average value of 0.0103, the n value at half-depth should be about 0.013. This is identical with the usual design value, which is based largely on measured values in seu-ers fiowing partially full.

I . Seasonal Change. Owing to the seasonal growth of aquatic plants, grass, weeds, willow, and trees in the channel or on the b'anks, the value of n may increase in the growing season and diminish in the dormant season. This seasonal chnnge may cause changes in other factors.

J . Suspended bfakrial and Bed Load. The suspended material and t he bed load, whether moving or not moving, would consume energy and cause head loss or increase the apparent channel roughness.

AU the above factors should be studied and evaluated with respect to conditions regarding type of channel, state of Bow, degree of maintenance, and other related considerations. They provide a basis for determining the proper value of n lor a given problem. As a general guide to judgment, it mag be accepted that conditions tending t o induce turbulence and cause retardance will increase n value and that those tending t o reduce turbulence and retardance u-ill decrease n value.

Recognizing several primary factors affecting the roughness coefficient, Cowan [32] developed a procedure for estimating the value of n. By this procedure, the value of n may be computed by

where no is a basic n value for a straight, uniform, smooth channel in the natural materials involved, nl is a value added t.a no to correct for the effect of surface irregularities, np is a value for variations in shape and size d the channel cross section, na is a value 'for obstructions, n, is a value for vegetation and flow conditions, and r n b is a correction factor for meandering of channel. Proper values of no to n, and m, may be selected from Table 5 5 according to the given conditions.

1 T t a n/np curve. was bmed on memuementa by Wilcox (281 on Sin. clay ndd concrete newer pipee and by Yernell and Woodward 1301 on open-buttjoint concrete nnd clay b i n tiles 4 to 12 in, in sue. For depths lms than about 0.15dp, tho ~urvc was verified by tbe &la of Johnson 1311 for large sewem.

DEVELOPMENT OF UKIFORM FLOW AYD ITS FORMULAS 107

In the value of nl, the degree of irregularity is considered mooih for surfaces comparable to the best attainable for the materials involved; minor for good dredged chnnnels, slightly eroded or scoured *ide slopes of canals or drainage channels; moderate for fair to-poor dredged

moderately sloughed or eroded side slopes of canals'or drainage e b n n e l ~ ; and seuere for badly sloughed banks of natural streams, badly

or sloughed sides of canaIs or drainnge channels, nnd unshaped, jngged, and irregular surfaces of channels excavated in rock.

I n selecting the value of ns, the character of varintions in size and shape of cross section is considered mhen the change in size or shspe occurs gradually, alLernaiing occasionally when large and small sections alternate occasionaIly or when shape changes cause occasional shifting of main Row from side to side, and alternuling jrequenlly when hrge and small sections alternate frequently or mhen sbap'e changes cnuse frequent shifting of-main flow from side to side. The selection of the value of nl is based on the presence and character-

istics of obstructions such as debris deposits, stumps, exposed roots, boulders, and fallen and lodged logs. One should recall that conditions considered in other steps must not be reevnluated or double-counted in this selection. In judging the relative effect of obstructions, consider the following: the extent to which the obstructions occupy or reduce the average water ares, the character of obstructions (sharvdged or angular objeck induce greater turbulence than curved, smooth-surfabed objects), and the position and spacing of obstructions transversely and longitudi- nally in the reach under consideration.

In selecting the value of n,, the degree of effect of vegetation is considered

(1) Low for conditions comparable to the following: (a) dense growths oi flexible turf grasses or weeds, of which Bermuda and blue grasses are ~ ~ a m p l e s , where the average depth of Bow is 2 to 3 times the height of vegetation, and (b) supple seedling tree switches, such ns willow, cottonwood, or salt cedar where the average depth of flow is 3 to 4 times the height of the vegetntion.

(2) Medium lor conditions comparable to the following: (a) turf grasses where the average depth of flow is 1 t o 2 times the height of vegetation, (b ) stemmy grasses, weeds, or tree seedlings with moderate cover where the average depth d flow is 2 to 3 times the height of vegetntion, and (c) bruehy growths, moderntely dense, similar to willowa 1 to 2 yeare old, dormant aeaaon, along side slopes of a channel with no significant vegetation along the channel ,bottom, where the hydraulic radius ia grater than 2 ft.

(3) High for conditions cornperable to the following: (a) turf graasea ber re the avernge depth of flow i~ about equal to the height of vegetntion,

108 UNIFORM FLOW

(b) dormant season-willow or cottonwood trees 8 ta 10 years old, inkr- grown with some weeds and brush, none of the vegetation in foliage, I where the hydraulic radius is greater than 2 it, and (c) growingaeason- bushy willows about 1 year old intergrown with some weeds in full foliage along side slopes, no significant vegetation dong channel bottom, where hydraulic radius is greater than 2 It.

(4) Very high for conditions comparable to the following: (a) tud grasses where the average depth of Aow is less than one-half the height of vegetation, (b) growing season-bushy willows about 1 year old, inkr- grown with weeds in full foliage along side slopes, or dense growth of cattplils along channel bottom, with any value of hydraulic radius up to 10 or 15 f t , and (c) growing season-trees intergronm with meeds and brush, all f n full foliage, with any value of bydraulic radius up to 10 or 15 It.

In selecting the value of m,, the degree of meandering depends on the ratio of the meander length to the straight length 01 the channel reach. The meandering is considered mimr for ratios of 1.0 to 1.2, appreciable for ratios of 1.2 to 1.5, and severe lor ratios of 1.5 and greater.

In applying the above method for determining the n value, several things should be noted. The method does not consider the effect of suspended and bed loads. The values given in Table 5-5 mere developed from a study of some 40 t o 50 cases of small and moderate channels. Therefore, the method is questionable when applied to large channels n-hose hydraulic radii exceed, say, 15 ft. The metbod applies only to unlined natural streams, floodways, and drainage channels and shows B

minimum value 01 0.02 for the n value of such channels. The minimum value of n in general, however, may be as low as 0.012 in lined channels and as 0.008 in artificial laboratory flumes.

6-9. The Table of Mannhg's Roughness Coefficient Table 5-6 gives a list of n values for channels of various kinds.' For each kind of channel the minimum, normal, and maximum valyes of n are shorn. The normal values for artificial channels given in the table are recommended only for channels with good maintenance. The boldface figures are values generally recommended in design. For the case in which poor maintenance is expected in the future, values should be increased according to the situation expected. ~ a b f e 5-6 will be found very useful as a guide to the quick selection of the n value to be used in a given problem. A popular table of this type was prepared by Horton [34] from an examina- tion oi the best available experiments a t his time.' Table 5-6 is compiled

T h e minimum value lor Lucite w m observed in the Hydraulic Engineering Labori- CPry a t the University of Illinois 1331. Such a low n value may perhaps be obtained also io~.smooth brllss and glass, but no observetions have yet been reported.

A Lable sbowhg n values and other elemeats from 269 obseri-stioas made on mang &Ling artificial cbannela i e also given by King 1351.

DEVELOPMENT OF UNIFORM FLOW AND IT9 FORMULAE 109

I Earth

hfeterial

Minor Degree of

0.005

irregul~rity hloderate

Rock cut 0.025

Fine gravel 1 I 0.024

Coarse gravel

SmooLh

Variations or channel cmxi section

0.028

0.000

Severe 0.020

0.000 Gradual

.4lternaiiag occnsionalIy 0.005

Alternaiing frequently 0.0104.015

Relative eEect of obatructiona

1 Severe I

vegetation I High ( nd 1 0.0254.050

-I 1 hlinor 1-1 1.000

( severe 1 1 1.300

Degree of meandering

A-TO

Appreciable I r n . ( 1.150

110 UNIFORM FLOW

TABLE 5-6. VALVES OF W E R O U ~ H H E S S COEPFICIEHT n (BoldIacc 6gure.s are values generally recommended in design)

Type of channel and description A. CLOSED COKDUITS FLOWINO PARTLY FULL

A-1. M e t l a. Brass, amootb b. Steel

1. Lockbar and welded 2. Riveted and spiral

c. CasC iron 1. Coekd 2. Uneoetid

d. Wrought iron I. Black 2. Galvanized

e. Corrugated metnl 1. Subdrain 2. Smrm drain

A-2- NonmeZal a. Lucite b. Glass c. Cement

1. K a t , aurlace 2. hior tar

- d . Concreta 1. Culvert, ntraight and free of debrin 2. Culvert with hen&, eonnectiona,

and some debris 3. Finisbed 4. Sewer with manholes, inlet, ete.,

stram 6. Unhoiehed, steel form 6. Unfinished, smooth wood Corm 7. Un6niebed, rough wood form

c. Wood ' I. Steve

2. L m i n n k d , treated #. C ~ Y

1. Common drainage tile 2. Vitrified sewer -

a. Vitrified newer wifh msnbolem, inlet, etc.

4. Vitrified nubdrain with open joint p. Brickwork

1. Glazed 2. Lined nilh cement mortu

h. Sanitary sewers mated with sewage nlimcs, with bend0 rod connecbonr

i. Paved invert, newer, rmwtb bottom j. Rubblc masonry, cemented

hlinimum

0.009

0.010 0.013

0.010 0.011

0.012 0.013

0.017 0.021

0.008 0.009

0.010 0.011

0.010 0.011

0.011 0.013

0.012 0.012 0.015

0.010 0.015

0.011 0.011 0.013

. 0.014

0.011 0.012 0.012

0.018 0.018

Nor~nal

0.010

0.012 0.010

0.013 ; 0.014.-

0.014 0.016 . 0-Ole 0.024.

0.009 0.010 '

0.011 0.013 "

0.011 0.013

0.012 0.015

0.013 0.014 0.017

0.012 0.017

0.013 0.014 0.015

0.016

0.013 0.015 0.013

0.018 0.025

.hIaximum - 0.013

0 Q)q 0.017

0;014 0.016

.0,015 0.017

0.021 0.030'

0.010 9.013

0.013 0.015

0.013 0.014

0.014 9.017

0.014 0.016 0.020

.0.014 0.020

0.017 0.017 0.017

0.018

0.016 0.017 0.018

0.020 0.030

from up-todate information collected from various sourccs ([34,36,3g], and unpublisbed data) ; hence it is much broader in scope thnn the Hortoa table. 6-10. Illustrations of ChameIs with Various Roughnesses. P b o h

graphs of n number of typical chnnnels, accompanied by brief descriptions of the channel conditions and the corresponding n values, are shotvn in Fig. 5-5. These photogrnphs Ere collected from different cources and arranged in order of increasing magnitude of the n values. They provide a general idea of the appearance of the channels having diff etent n. values and so should facilitate selection of the n value for a given channel con. dition. The n value given for each channel represents approximately the coefficient of rough- when the photograph vas taken.

The above type d visual aid is ako employed by the q.6. Geological Survey. The Survey hns made several determinations of chaanel roughness in streams, mostly in the northnpestern United States. These include measurements of cross-sectionnl area, width, depth, mean velocity, slope, and computation of the roughness coefficient. The reachea mere pbotographed in stereoscopic color, and the photographs have been circulating among the district offir-ea of the Survey as a guide in evaluating n.

MATER SUPPLY AND POLLUTION CONTROL

changes in grade, pipe size. dircclion oi flow, a n d quantily of flow. F i ~ u r c 6-14 illustrales ~ h t details of a typical manhole. Storm drains a r e usually no! b u i l ~ smaller t h a n I 2 in. in diameter, because pipes or lesser s i t e l end ro clog readily with debris and rhcrcrore present serious rnal iunc~ion problems. Maximum manhole spacing Tor pipes 27 in. and under should not excccd about 600 CI. For larger pipes. no maximum i s prescribed a n d the normal requiremenls Tor slruclures should provide access ro the dra in Tor inspeclion. cleaning. or maintenance.

6-18. HYDRAULIC DESIGN OF URBAN STORM-DRAINAGE SYSTEMS

Basic principlcs oullined a t the beginning of t h e chapter arc sufi- cient lo adequa~cly design an urban drainage system. Calculations for the d r a i n a ~ e area shown in Fig. 6-15 are presented in detail ro i l l u s l r a~c he mechanical procedure and the ralional method as applied i o a n actual design problrm. The overall M e x i e x area is an urban residential arca rnadc up or single-Family dwellings and is divided into 8 subareas which are 1ribu1ar)- 10 individual s~orm-waler inlets.

E X ~ M P L E 6-4. Dcsign a s~orm-drainage syslcrn to carry the flows from the # inlel areas given in Fig. 6.15. I t will be assumed thar a lomycar rrequency rainVal1 satisfies he local dcsign requirements. Assume clay soil 10 be prc- dominanl in the area u ith average l awn slopes.

Solurion: The sleps for solving are as rollows: 1 . Prcpare a drainage-area m a p showing drainage limi~s, srrccls, impervious

areas. and dirccrion orsurrdcc Row. 2. Divide the drainage arca into subareas ~ribulary ro the proposed slorrn-

water inlets (Fig. 6-15). 3. Compute !he acreage and imperviousness or each arca. 4. Calculalc the required capaci~y of each inlet, using the ra~ional melhod.

Assume a 5-min inlel lime to be approprialc and cornpule inler flows lor a rainfall in~ensity of 7.0 in./hr. This is obtained by usinp ~ h c Lomycar frequency curve on Fig. 6-1 1 with a 5-min conccntrarion lime. .,Appropriate C value!, arc obtained rrom Fig. h-10 hj- tntcring the graph wirh thc calculalcd percenlagc imperviousness (the pcrccnl or the inlcl area which i s covered b! siretrh, sidtwalks. drives, rools, etc.). projecling up-10 the average lawn slope curve and reading C on the ordinarc. Compu~arions Tor the inlet flows arc tabulaled in Tablc 6.7.

5. Select the type inlc~s required lo adequalel) drain the ROW'S in Table 6-7. The choice will be hascd on a Lnowlrdge of the slreet slopes and lheir relation to various inlet capacities. lnlcr capaci~y curvcb such as given in Fig. 6-1 3 would be used. For the purposes of this c~arnple. no actual seltclions will bc made b u ~ the sludcnt should rccognizc t h a ~ this is the next logical step a n d an exceedingly irnportanl one.

6. Beginning al the upstream end o i the syslcm. corn pure the discharge lo be carried b! each successire lcngrh of pipe. mot-ing downslrcam. These calculations arc summarized i n Tablc 6-8. Kote lhal at each point downslream ~ h c r c a

Waste-Water Systernl

T A B L E En I N L E T C

-7 PACITIES FOR EXAMPLE 6-5

Q.

new flow is inlroduced, a neu lime of conccnlra~ion must be dclerrnined as well as new values of C and drainage arca size. As the upslream inlet areas a r t combined to produce a larger tributary arca a1 some design poin~, a revised C value represenling these combined areas mus! be ob~aincd. Usually Ihc procedure is to lakc a weighted average o i all the individual C values or which the larger arca is compostd. For example, when cornpuling the flow lo be carried by he pipe from M-9 to M-8. the ~ r i b u ~ a r j , arca is A + B + C = 6.46 acres, and the composite valuc of C will be

AI ~ h c design localion ~ h t value or I, will be equal to the inlet Lime at 1-8 plus the pipe Aou- rime rrom I-F 10 M-9 (see Table 6-81, which ,pus1 be known 10

permil solving rhr rainrall inrensitv 10 bt used in computing the runoff rrom composite arca A + B + C.

7. Using t h e compu~ed discharge values. sclecl tentative pipe sizes tor the approximate slopes given i n column 8 of Table 6-8. Once the pipc sizes are known, flow vcloci~ies bttwttn inpur localions can be delcrmined. Normally theseveloci- tics are approhimated by computing ihc Cull flow v t ~ o c i l i ~ s for maximum discharge at ~ h c specified grade. These vcloei~ies are then uscd to cornputc chanriel f l o h lime for es~irnaling the time of concenlralion. l r upon comple~ing the hydraulic design enough change has been made in any conccn~ralion time 10 alter the design discharge. new values or flow should b.e compuled: Generally rhis will no1 k t h t casc.

8. Using the pipe sizes stlected in Slep 7, draw a profile of the proposed drainage syslem. Begin the profile al the po in~ rarthest downsueam, which cdn be an ou~ia l l into a natural channel. an arlificial channel. or an existing drairi 8s in the casc of the example. I n construcling he profile, be certain thar he piper have at least the minimum required cover. Normally 1.5 lo 2 f t is suficien~. Pipe slopes should conrorm to [he surface slope wherever possible. Ai all rrhn- holes indica~e the necessary change in invert elevation. In this example where there is no change in pipc size through the manhole, a drop of 0.2 f~ will bc uscd. Where ~ h c size deercases upsircam through a manhole, he upstream inverl

Waste-Water Systems

will bc s c ~ above the downstream inver! a distance equal 10 lhc dilTcrencc in 1he two diameters. In this way [he crowns arc ktpl a t lhc same elcvalion. A par1 or the profile or thc drainage s ~ s l c m in the caamplc is given in Fig. 6-16.

FIG. 6-16. Profilc or par1 or the bl;xtcx slorrn drain. showing thc hydraulic pradien~.

9. Compute the pos i~ ion of the hydraulic gradient along the profile or the pipe. IT this gradient lies lrss lhan 1.5 fl bclou the ground surface, it mu51 lx Lowered LO preclude thc possibiliry oisurcharge during the design flow. Norc rhal the value of 1.5 i~ i s arbi~rar i ly chosen here. In practice. local s ~ a n d a r d s indicate thc limiting value. Hydraulic g r a d i e n ~ s may bc lon.crcd by increasing pipe sizes. decreasing head losses a[ structures. by designing special ~ r a n s i ~ i o n s . by lowering he system helow ground. or by some combinaiion of these mcans.

Cornputalions Tor a porrion of [he hydraulic pradicnt orlht eaarnplc will now be given. Head losses in 1 he pipcs are dcierrnined by applying hlanning's cqua- lion, assuming n = 0.01 3 in this c~arnplc. Head losses in the srructurcs will Ix dc~ermined by using he relaiionships defined in Figs, 6-1 7 and 6- 18. These curves were drveloped Tor surcharged pipes cnrcring rccrangular structures but may k applied t o wyc branches. manholes, and junction chambers as piclured on the

11

curves:- The "A" curvc is used lo find entrance and c x i ~ losses, the "B" curve lo cvaluate the hcad loss duc 10 an increased velocity in thc downs~ream dircclion. The loss is dcsignatcd as the difference belwcen he head losscs round Tor the downstrcam and upsiream pipe (V,-I - I n cases where ~ h c grea1csI velocity occurs upstream. the diRerencc will be negati\.c and may be applied lo ofse t other losses in ~ h c structure. The "C" loss resulls from a change in direclion in a manhole. wyc branch. o r bend slructurc. The "D" loss is rc la~cd

Heod Losses 3 0

-4: B : L . 0 2 - O 5 1 . : 0 . 5 1

2.8 c: D :

2.6 Total

Upstream flow, cls Downstream flow, cls Incoming volume, cfs Upstream velocity, Ips Downslream velocity, fps Velocrry head, II

2 4 / I l l 1

Wye branch 111 I I I I

Ve loc~ ly fi/5eC

FIG. 6-17. Types A . 0, and C hcad losses in slruclures. (Courlcsy or the &nlli- morc County Dcp;lrtmenl or Public Works. Towson. Maryland.)

10 the effects producrd by the tnlrance of secondary flows inlo ihe struclure. Several examples arthe use or these curves arc shauin an Figs. 6-17 and 6-18.

' Computa~ions for the hydraulic gradient shown in Fig. 6-16 are as f ~ l [ o w s : (a) Begin a! ihe elevation or thc hydraulic gradient at [he upslrcam end or

'he misting 30-in. reinrorccd-ecrncre~e culvert pipe (RCCP). This elevalion is 105.50. The enisling hydraulic gradien~ is shown on Fig. 6-16.

Wa~te-Woler Systems

D loss - 0; no secondary Row Total .: 0.36 ft

The hydraulic gradient thererorc rises i n the manhole ro an clcvation of 105.50 + 0.36 = 105.86 It, plorted in h.1-1 on Fig. 6-16.

(c) Cornpule the head loss due l o Friction in the 30-in. drain rrorn M-l 10

hl-'1. Assume n - 0.01 3. Using blanning's equation, the head loss per linear fool oldrain is

and rrorn hl-l lo M-2.

The total rrictional hcad loss i s rhererore

Eleva~ion o i the hydraulic gradient at ~ h t downs~rcarn end of M-2 is thus 105.86 + 1.73 = 107.59 r(. This elevation is plol lcd or; Fig. 6-16. and the hydraulic gradien~ in (his reach is drawn in.

(d) Compute the head losses in M-2.

A - 0.36 ( V = 8.3 irlsec) 8 - 1.07 - 0.90 = 0.17 ( V 2 = 8.3, I/,, 7 7.6 = Q/.4 for 27-in-drain) C = 0.20 x 2.0 (rnulliply by 2 Tor 90 degree bend in manhole-

see Fig. 6- 17) - 0.40 D = 0.22 Tor QJ/Ql - 1 1.3/30.3 = 37 percenl .. .

T o ~ a l hcad loss ili S1-2 equals 1-15 h and ,he clcvation or he hydraulic gradien~ in M - l i s thcreforc 107.59 + 1.15 = 108.74 1~.

(c) Compute the f r ic~ion head loss in the section oC pipe from M.2 to M-3.

Elevation or the hydraulic gradien~ a1 the downstream end of hl-3 is thercforc 108.74 + 0.47 = 109.16 Tt. Plot this point on the protile and draw tht gradient horn hl-2 to M-3.

Students should realize t h a ~ rhe hydraulic gradient in this example was computed under he a s s u m p ~ i o n or uniform flow. In closed c o n d u i ~ systems, if the pipes are flowing rull or he sysLem is surcharged (the usual design flow conditions), his rnrrhod will produce good resulls. Where open conduirs are used, or i n partial-flow systems, he hydraulic gradienl can be de~ermined by compl~i ing surlace profiles in the manner described in Sec. 6-2.

Computations tor the remai,nder o r he hydraulic gradient are i d r n ~ i - cal to those just given and will nut br: prescn ted. 11 should be noled that

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