Ents Arcata Urban Numerical Cbec 081808 Gg

ENTS Workshop, Humboldt State, August 18, 2008

Numerical Analysis for Urban HydrologyChris Bowles, Ph.D., cbec, inc.

Engineered Natural Treatment Systems Humboldt State University, Arcata, CA

August 19, 2008


Overview of Presentation

1. Overview of hydrologic models– Rational method– Regional regression/TR55– Spreadsheets– GIS modeling– HEC-HMF, HSPF - BAHM/WWHM

2. Overview of hydraulic models– Simple Manning’s Equation– 1D models - HEC-RAS– 2D models - MIKE 21


What are hydrology and hydraulics

hy·drol·o·gy [ hī dróllәjee ]

noun Definitions: study of earth's water: the scientific study of the properties, distribution, use, and circulation of the water on Earth and in the atmosphere in all of its forms

hy·drau·lics [ hī dráwliks ] noun Definitions: study of fluids: the study of water or other fluids at rest or in motion, especially with respect to engineering applications ( takes a singular verb )

http://encarta.msn.com/encnet/features/dictionary/Pronounce.aspx?search=hydrology

http://encarta.msn.com/encnet/features/dictionary/Pronounce.aspx?search=hydrology


Hydrology

Taken from Stream Corridor RestorationFederal Interagency Stream Restoration Working GroupOctober 1998


Hydrology



Hydrology



HydrologyTaken from Stream Corridor RestorationFederal Interagency Stream Restoration Working GroupOctober 1998




Hydrology





Hydrology!"#$# %"# $&'( )*#+,!"#$# %"# $&'( )*#+,

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Many Applications of Hydrologic ModelsHydrologic models are useful in

• Regional water supply planning• Managing water quality at basin-scale (e.g.,

TMDLs)• Instream flow protection• Flood hazard management• Permitting use (in/out-of-stream, ground water)

and discharge (wastewater)• Reservoir operations

Each application has specific geographic and temporal scopes and resolutions that influence model structure.


Application Dictates ApproachHydrologic models span a huge range in:

• output - the information you want, • input - the information you have, • resources needed for development - the

expertise, funding, and time available to construct and calibrate the model, and

• resources needed for maintenance - the expertise and time required to run the model.

Each of these should be considered when selecting an approach


Types of Hydrologic Models1. Statistical – IHA, regional regression2. Event – SCS curves, unit hydrograph

– Can be the primary runoff algorithm for continuous time-series models (e.g., USDA Soil and Water Assessment Tool, TR-55)

3. Continuous, spatially distributed – PRMS, TOPMODEL, HSPF, VIC2, DHSVM

4. Operational or water management – RESSIM, WEAP21


Rational Method

• Simple method for estimating runoff response from small watersheds

• Accounts for the following characteristics• Runoff abstraction

and diffusion (C)• Rainfall intensity,

duration, and frequency (I)

• Watershed area (A)

CIAQp =


Urban Flood Frequency

• USGS National Flood Frequency Program• Peak discharges for rural and urban areas• Flood hydrograph estimation techniques

• Urban peak discharge (nationwide equations)

•UQ10 = urban peak discharge (cfs)• A = watershed area (square miles)• SL = main channel slope (feet/feet)

( ) ( ) ( ) 58.007.030.057.075.115.032.010 101383299.2 RQIABDFSTRISLAUQ −− −++=

• RI2 = 2-hour, 2-year rainfall (inches)• ST = watershed storage (e.g. lakes, wetlands, etc.)• BDF = development factor (e.g. channel mod’s and

linings, storm drains, curb & gutter)• IA = percent imperviousness • RQ10 = equivalent rural peak discharge


Urban Flood Frequency (cont’d)

• Rural peak discharge (state/region equations)Example, 10-year, North Coast RegionUse gage data when available (area w/in 50 to

150%)

RQ10 = rural peak discharge (cfs)A = watershed area (square miles)P = mean annual precipitation (inches)H = altitude index (thousands of feet)

27.093.088.021.610 −= HPARQ( ) 88.0gagedungagedgagedungaged AAQQ =


TR55 Method

• NRCS simplified procedures for small to midsize urban watersheds to calculate:• Peak discharges• Flood hydrographs• Stormwater storage volumes

• Two main procedures• Graphical for peak discharges (tc: 0.1 to

10.0 hrs)• Tabular for flood hydrographs (tc: 0.1 to 2.0

hrs)


TR55 Method (cont’d)• Watershed inputs

• Composite CN• Travel time• Storm type• Peak discharge• P2 = 24 hour, 2-year rainfall depth • Qp = peak discharge (cfs)• Qu = unit discharge• A = watershed area• Q = 24-hour, n-year rainfall depth• F = surface storage correction factor

( )4.05.0

2

8.0007.0SPnLtc =

AQFqQ up =


Curve Runoff Number Method

• NRCS empirical method for rainfall abstraction• Potential storage (S) related to a curve

number (CN)• Effective rainfall producing runoff• Q = effective rainfall (inches)• P = rainfall at time t (inches)• S = storage (inches)• Ia = initial abstraction (typ. 0.2 times S)

( ) ( )( )( )( )IaStP

IatPtQ−+

−=

2

101000−=

CNS


Curve Runoff Number Method (cont’d)

• CN is a function of soil type, land use, imperviousness, and antecedent moisture



Elevation

Land Use

HydrologicSoil Type

Curve Number

Images courtesy of PWA




Useful Web Siteshttp://www.lmnoeng.com/Hydrology/hydrology.htm

8/18/08 10:38 AMHydrologic calculation for storm runoff discharge and curve numbers for watersheds

Page 1 of 7http://www.lmnoeng.com/Hydrology/hydrology.htm

SCS TR-55 Peak

Discharge and

Runoff Calculator

Hydrologic calculations for Peak Discharge, Runoff Depth,

Runoff Curve Number, Time of Concentration, and Travel

Times

Based on the USA Soil Conservation Service publication TR-55 (1986):Urban Hydrology for Small Watersheds

To: Precipitation maps for 24-hr duration storms in USA

Detention Basin Volume Calculation Other Time of Concentration Equations Rational Equation for Peak Discharge Unit Conversions

LMNO Engineering home page Trouble printing? Register

Topics on this page: Introduction Equations Runoff Curve Numbers Error Messages References

Register to enable "Calculate" button

Flow (and Channel) Len…Travel Time Information

0.0Curve Number for Region 5, CN5:

0.0Area of Region 5, A5 (mi!): Region 5:









Curve Number Information

0.0Ponds, Swamps (% of Total Area):Precipitation (and Runo…

4.5Precipitation, P (inch):Rainfall Distribution Ty…

INPUTS

Will be computedTime of Concentration, Tc (hr):Time of Conc., Travel T…

Will be computedOverall Curve Number, CN:Area in mile!

Will be computedTotal Watershed Area, A (mi!):Select Units:

Enter these three quantities: INPUTS OR OUTPUTS

Will be computedInitial Abstraction, Ia (inch): http://www.LMNOeng.com

Will be computedPond and Swamp Factor, Fp:Research, and Software, Ltd.

Will be computedUnit Peak Disch., Qu (cfs/mi!-inch):© 1999 LMNO Engineering,

Will be computedRuno", Q (inch):Peak Discharge in cfs o…

Will be computedPeak Discharge, Qp (ft#/s or cfs): OUTPUTS

Click to Calculate Not registered user Reset Inputs to 0.0

8/18/08 10:38 AMHydrologic calculation for storm runoff discharge and curve numbers for watersheds

Page 2 of 7http://www.lmnoeng.com/Hydrology/hydrology.htm

Will be computedTravel Time, Tt (hr):

0.0010Water Surface Slope, S (ft/ft):

900.0Channel Length, L (ft):Channel Dimensions in ft

0.03Manning n for Channel Flow:Natural Stream: Clean, …

0.5Channel Depth, y (ft):Trapezoidal Open Channel

6.0Channel Top Width, T (ft):Select Geometry, Material, Units

3.0Side Slope, z (Horiz/Vert in decimal):Channel Flow:

Will be computedTravel Time, Tt (hr):Unpaved

0.0020Surface Slope, S (ft/ft):Select Paved or Unpaved

600.0Flow Length, L (ft):Shallow Concentrated Flow:

Will be computedTravel Time, Tt (hr):

0.0050Surface Slope, S (ft/ft):

0.4Manning n for Sheet Flow:Woods: Light underbrush

2.52-yr, 24-hr Rainfall, P2 (inch):Select Ground Cover

200.0Flow Length, L (ft):Sheet Flow:

Flow (and Channel) Len…Travel Time Information

Introduction Top of PageThe USA Soil Conservation Service (now called the Natural Resources Conservation Service), division ofthe USDA (USA Department of Agriculture) has worked for decades developing equations and conductingexperiments to determine reliable models for predicting peak discharge from storm events. Relying uponextensive research, Technical Release 55 (TR-55: SCS, 1986) presents a methodical and reliable approachto predicting peak discharge due to a 24-hr storm event. (This web page uses TR-55 and SCS (1986)interchangeably; they are the same document.) TR-55 is valid for watersheds that have a time ofconcentration from 0.1 to 10 hr. Such watersheds are considered small. Our calculation uses the equationsand graphs (coded into equations) in TR-55 chapters 1 thru 4 to solve for peak discharge. Chapter 5 (titledTabular Hydrograph Method) also solves for peak discharge but models more complicated watersheds -watersheds that have several main channels requiring channel hydrograph routing techniques. Hydrographrouting software is more suitable for stand-alone computer programs rather than for programs that run fromthe world wide web.

Though the TR-55 document mentions specific units (all English) for its equations, our calculation allows avariety of input and output units (English and metric). We have tried to make the calculation useful for theinternational community. Unfortunately, TR-55 only presents rainfall distribution maps for the USA. Therefore, non-USA users need to determine whether a typical 24-hr rainfall resembles a Type I, IA, II, orIII distribution and determine 24-hr rainfalls from local sources. Our calculation was written in doubleprecision using the Java computer language.

Equations (SCS, 1986) Top of PageTR-55 specifies units for its equations. Our calculation allows you to use other units that may be moreconvenient. Peak discharge, runoff depth, initial abstraction, unit peak discharge, and pond/swamp factorare computed as follows:

http://www.lmnoeng.com/Hydrology/hydrology.htm

http://www.lmnoeng.com/Hydrology/hydrology.htm


Useful Web Siteshttp://rational.sdsu.edu/onlinecurvenumber.php

8/18/08 10:41 AMRunoff calculation based on curve number, Victor Miguel Ponce, San Diego State University

Page 1 of 2http://rational.sdsu.edu/onlinecurvenumber.php

online_curvenumber: Runoff based on NRCS curve number

Formula

Q =

f(P,CN)

References

Ponce, V. M.,1989.

EngineeringHydrology,Principles

andPractices,

Prentice Hall,pages 156-

158.

♦ ♦ ♦

Runoff curvenumber: Has

it reachedmaturity?

INPUT DATA:

Watershed (optional):

Units:

SI (metric)

U.S. Customary

(SI units) [U.S. units]

Event precipitation P (cm) [in]:

Curve number CN:

OUTPUT:

Please enter inputdataand press'Calculate'.

⇐ ⇐ ⇐

Calculate Reset

Your request was processed at 10:41:33 am on August 18th, 2008 [080818 10:41:33 ].

8/18/08 10:41 AMRunoff calculation based on curve number, Victor Miguel Ponce, San Diego State University

Page 2 of 2http://rational.sdsu.edu/onlinecurvenumber.php

Thank you for running online_curvenumber. Please call again. [080321]

online calc

normaldepth

criticaldepth

discharge inculvert

critical slopesequentdepth HJ

energy loss HJ

dischargesluice

dischargeweir

dischargechannel

initial sequentHJ

criticalconstriction

efficiency HJ

M1wsprofile

M2wsprofile

M3 wsprofile S1 wsprofile S2 wsprofile S3 wsprofile

C1wsprofile

H2wsprofile

A2 wsprofile C3 wsprofile H3 wsprofile A3 wsprofile

tractive forceogee

spillwayHazen-Williams

creager rational slope-area linear reservoirstorage

indication 1storage

indication 2

MuskingumMuskingum-

Cungetime-area Clark UH cascade of linear reservoirs

Blaney-Criddle

PenmanPenman-Monteith

Thornthwaite Priestley-Taylor

Gumbel Gumbel 2 Log Pearson Log Pearson 2TR-55

graphicalconvolution

S-hydrograph

curvenumber

time of concentration

hyperbolic regressionone-

predictorlinear

one-predictornonlinear

two-predictor

linear

two-predictornonlinear

USLEDendy-Bolton

Shields Duboys Colbyreservoir

design life

http://rational.sdsu.edu/onlinecurvenumber.php

http://rational.sdsu.edu/onlinecurvenumber.php


It’s OK to fall to sleep...


Spreadsheet Methods

Example from Greg Gearheart


GIS Methods - Stream Susceptibility Mapping

Tier 1- Susceptibility map. Specific stream power (effective discharge x stream slope) to map areas of high stream erosion potential.

Tier 2 - Conduct rapid geomorphic assessments for selected areas that were screened as high and low erosion potential in Tier 1.

Tier 3 - Identify key geomorphic thresholds (e.g., relationship between channel slope, median particle size, and drainage area for stable and unstable channels, critical bank heights in various channel materials, channel response to changes in flow and sediment supply, etc) from comparison of stable and unstable channels.


Stream Susceptibility Mapping

Nh = Sex / SeqSeq = a*(d50/A)^b where a ranges from 0.007 to 0.010, d50 is 0.5 mm (typical sand value considering the soils; applied uniformly), A is area in km^2, and be is 0.6

Per Hack's relationship:


Stream Susceptibility MappingPer Streampower:

StmPowerW = SW*(Q/B)*S [Watts/m^2]


Erodibility Mapping

StmPowerW = SW*(Q/B)*S [Watts/m^2]


Management Strategy Table

CEM Type

Hydraulic Stability Number

Bank Stability Number

Management Strategies

I 1 <1 None needed

I & II >1 <1 Grade control, local bank stabilization may be necessary to protect structures, riparian habitat as equilibrium slope is re-established

III >1 >1 Grade control and local bank stabilization to protect structures and riparian habitat or flow duration control

III & IV <1 >1 Bank stabilization with grade control emplacement or flow duration control

IV & V <1 <1 Local bank stabilization and habitat enhancement features


HEC-Hydrologic Modeling System

HMS – designed to simulate rainfall-runoff processes in denditric watershed systems


Continuous Simulation Modeling1. Simulates long-term

response of a watershed to rainfall

2. Inputs: Long-term rainfall & evaporation records; data on landform, land cover, soil properties

3. Outputs: Time series of runoff flows; accounting of water balance; storage/flows in pipes and other facilities

4. Requires calibration of parameters to match existing flow data


Advantages of Continuous Simulation Models

1. Ability to determine antecedent conditions (e.g., soil moisture, ground water table, surface storage, etc.)

2. Ability to generate a long term flow record for statistical analyses

3. Ability to more explicitly represent interactions of surface runoff with inflow and groundwater


Often Used for Evaluating Hydromod Requirements

1. Generate pre- vs. post-project flow duration curves using hydrologic model

2. Continuous simulation required3. Most widely used models in U.S.:

– EPA HSPF - WWHM, BAHM– EPA SWMM– USACE - HEC-HMS


Bay Area Hydrology Model

1. Tool to size flow control facilities to meet hydromodification requirements

2. Developed based on the Western Washington Hydrology Model and HSPF

3. Jointly funded by the Santa Clara, Alameda, and San Mateo countywide stormwater programs

4. Calibration to local watersheds



Features:1. Has user-friendly

interface to HSPF2.Loads appropriate

parameters based on project location

3. Uses long-term local rainfall records

4. Simulated pre- and post-project hydrology and automatically sizes a facility to match pre- and post-project flow duration curves



Project Data Input Screen(Pre- and Post-Project

Flow Control Facility Input Screen



Can Represent the following LID BMPs:

• Permeable Pavement• Dispersion• Green Roof• Rainwater Harvesting• Rain Garden• In-Ground (Infiltration)

Planter

• Flow-Through Planter• Bioretention Area• Vegetated or Grassy

(Dry) Swale• Dry Well• Infiltration Trench• Infiltration Basin/Pond



The BAHM provides:• An easier, standardized

way to do continuous simulation modeling

• A means to compute flow control benefits of site design and treatment measures

• Standardized reporting to assist municipal staff in design review

Output Screen


Flow Duration Control Approaches


Sizing Factor Approach for Flow Control

• Contra Costa Clean Water Program developed combined treatments and flow control sizing factors for IMPs

• Used HSPF models to simulate runoff for 30 years from hypothetical 1-acre site (undeveloped and completely impervious) to each IMP

• Factors reflect minimum size of IMP that matches pre-project flow duration Opening Screen: Project

Information


Sizing Factor Approach for Flow Control

IMP-Specific Sizing Information

IMP Types

• In-Ground (Infiltration) Planter

• Flow-Through Planter• Bioretention Area

• Vegetated or Grassy (Dry) Swale

• Dry Well• Infiltration Trench


Contra Costa - Integrated Management Practices (IMP)


Overview of Hydraulic Models

• Various dimensions of numerical modeling

• Applicability of models for different scenarios: hydraulic, temperature, sediment transport, water quality

• Relative costs (numerical and financial)

• Relative limitations of models of different dimensions (0-D, 1-D, 2-D and 3-D)

• Criteria for the selection of suitable models


And now for the intuitively obvious...

∂∂

+

∂∂

+

+

−

∂∂

=

∂∂

+

∂∂

i

j

T

j

i

T

ij

j

j

i

ji

xU

xU

kP

x

xU

Ut

U

ν

νδ

ρ

32

1

G.G. Stokes1819-1903

C.L.M.H. Navier1785-1836


Hydraulics



Hydraulics



What can we do with a hydraulic model

Define Existing Conditions – sediment transport, velocity, water surface elevation, temperature, water quality

Detailed Design – channel shape, longitudinal profile, morphological and hydraulic diversity, sustainability

Stability Assessments – bed, bank, allowable velocities, allowable shear stress, sediment yield and transport

Predict morphologic evolution


What can’t we do with a hydraulic model


Which dimension for which job?

Muddling Through Modeling - An Introduction to Fluvial Hydraulic

Modeling Applications for Non-Engineers – February 2005

WHICH DIMENSION FOR WHICH JOB?– Large scale flood

analyses (reaches on

the scale of miles)

– Sediment transport,

water quality modeling

at the reach scale

– Morphological

modeling

– Floodplain modeling

– Flow around

structures (obstacles

such as groins, ELJs,

etc)

1D

3D

2D

Degre

e o

f Appro

xim

atio

n

_

+


Which dimension for which job?



WHICH DIMENSION FOR WHICH JOB?

1D Steady State

3D

1D Dynamic/Unsteady State

1D Looped/Unsteady

2D

Increasing time

Increasing cost

Increasing data requirements

0D (Mass Balance)Choose the most

appropriate tool to

answer the questions…


Range of models



Range of Models

Advection-Dispersion

Water Quality

Sediment Transport

BOD + DO + N

Eutrophication

Heavy Metals

Non cohesive Sediment Transport

Cohesive Sediments Transport

Morphology

Hydrodynamic

Rainfall Runoff


Data Requirements• Availability of data important in

selection of model• No point applying complex 3D if only

cross section information is spaced at one mile intervals and is 10 years old!

• Should be sufficient data to:• Understand recent historic evolution of

channel• Calibrate model based on recent

hydrologic event• Validate performance of model based on

independent hydrologic event• Verify predictions of model using post

project data• Confirm long term viability of project by

establishing long term monitoring program


Calibration & ValidationMIKE11 Calibration

1260.5

1261.0

1261.5

1262.0

1262.5

1263.0

Mar-91 Sep-91 Apr-92 Oct-92 May-93 Nov-93 Jun-94 Jan-95 Jul-95 Feb-96 Aug-96 Mar-97 Sep-97 Apr-98

Date

WSL

[m]

Rattlesnake Point - Measured

MIKE11 HD - Simulated


The process of modeling

• Model specification• Data assembly and

verification• Model building• Model calibration and

validation• Sensitivity testing• Model application to

generate the required outputs


Representation of physical processes

•Included explicitly through physically based equations – basic laws of fluid motion

• Included as parameterized relationships for empirical (or semi-theoretical) representations where dimensionality or grid resolution restricts explicitly representation

• With model dimensionality and grid resolution increases then more physical processes can be represented explicitly rather than by empirical relationships


Representation of physical processes



SUMMARY OF GOVERNING EQUATIONS

••1-D Steady

(BW curve)

••1-D Steady

(Flood routing)

••1-D Unsteady

••••3-D

•••2-D

•0-D

Conserv. of

Momentum

(x, y, & z

directions)

Conserv. of

Momentum

(x & y

directions)

Conserv. of

Momentum

(x

direction)

Conserv.

of Energy

Conserv. of

Mass (aka

Continuity)


Relative Cost (Financial & Computational)



RELATIVE COSTS – Financial & Numeric

MIKE 3, CCHE3D,CH3D, Trim3D,SSIIM, Telemac,TriVAST, Fluent

MIKE 21,SMS(RMA), River

2D, CCHE2DTelemac, DIVAST

HEC-RAS, MIKE11, ISIS, RMA

HEC-RAS, Excel,HEC-1, HEC-6

Excel, MATLab

Examples

Detailed modeling of flowstructures

Weeks tomonths

ResearchLES, DNS

Hydrodynamic modelingHours toweeks

$0 –$100,000

3D

Hydrodynamic modeling,sed. transp., water quality

Minutes todays

$0 –30,000

2D

Hydrodynamic modeling,sed. transp., water quality

Minutes tohours

$0 -$5,000

1DUnsteady

Backwater modeling,standard step, hydrology,

sed. transp.

Minutes$01D Steady

Spreadsheet programming,simple hydraulics,

hydrology, sed. transp., etc

Seconds tominutes

$0 - $1000D

ApplicationNumericalCost

$ CostDimension


2D Example


3D Modeling



And Remember...

“All models are wrong; some are useful.”

W. Edwards Deming

“It is better to be roughly right than precisely wrong.”

John Maynard Keynes


Story of hope...


Useful References

• SCVURPPP HMP:www.scvurppp.org

• Bay Area Hydrology Model:http://www.bayareahydrologymodel.org/

• Contra Costa IMP Sizing Tool:http://www.cccleanwater.org/new-developmentc3/stormwater-c3-guidebook/

http://www.scvurppp.org/

http://www.scvurppp.org/

http://www.bayareahydrologymodel.org/

http://www.bayareahydrologymodel.org/

http://www.cccleanwater.org/new-developmentc3/stormwater-c3-guidebook/





Acknowledgements

• Eric Berntsen, SWRCB.• Chris Campbell, cbec, inc.• Ron Bottorff, Friends of Santa Clara River.• Jill Bicknell, EOA, Inc.• Peter Goodwin (U Idaho), Andy Ward (Ohio

State), Jeff Opperman (TNC), Jeff Mount, Peter Moyle, Katrina Schneider (SYRCL), Roman Loranc (photographer).


Questions?

Dr. Chris [email protected]

(916) 570-2502(916) 243-8290

mailto:[email protected]

mailto:[email protected]

http://www.cbecoeng.com

http://www.cbecoeng.com

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