DRAINAGE STUDY - Mauriello Planning...

DRAINAGE STUDY

645 Beard Creek Trail

Lot 8, Cordillera Valley Club Filing No. 1

Eagle County, Colorado

November 25, 2014

Project No. 14-2953

Prepared for

Mr. Robert Myers

Caribbean Group

P.O. Box N 1968

Nassau, Bahamas

P.O. Box 2837, Edwards, CO 81632 Tel (970) 926-9088 www.lkpengineering.com

DRAINAGE STUDY

TABLE OF CONTENTS:

SCOPE OF STUDY………………………………………………………..........…….......1

SITE DESCRIPTION………………………………………………………..…………....1

RECORDS RESEARCH……………………………………………………..…………...2

DRAINAGE BASIN………………………………………………………...……..….......2

DRAINAGE CRITERIA………………………………………………...………...……...2

FINDINGS AND RECOMMENDATIONS……………………………………….…...3-6

LIMITATIONS…………………………………………………………………………....6

APPENDIX A

WinTR-55 STUDY

SOILS STUDY

RAINFALL INTENSITY

LKP Engineering, Inc.

DRAINAGE STUDY

SCOPE OF STUDY

This report represents the results of our drainage study, which incorporates a site

reconnaissance, reviews of existing documents and records, calculations, and analysis of

the information. The purpose of the study was to evaluate the existing conditions of the

site with respect to the runoff from 2 and 100-year storm event, to verify the capacity of

the existing 30-inch culvert, and to provide design recommendations for a drainage

swale.

SITE DESCRIPTION

The site is located at 645 Beard Creek Trail, Lot 8, Cordillera Valley Club Filing

No.1, Eagle County, Colorado. It is on the uphill side of the road, and the topography of

the site is steep to moderate sloping to the south. The lot is between approximate

elevations of 7400 and 7460 feet above sea level. The vegetation consisted of sage

brush, juniper and sparse wild grass. On the west side of the property is Deadhorse

Gulch with a watershed of about 138 acres. The Deadhorse Gulch is crossing under

Beard Creek Trail, near the southwest corner of the lot, through an existing 30-inch,

corrugated plastic culvert. Approximately the west half of the lot is within the Deadhorse

Gulch Watershed. There are several dry gulches running through the lot and the

watershed area. Two dry gulches run from the northeast corner of the lot toward the

proposed building site. There is another dry gulch running along the eastern property

line. This gulch is discharging into a catch basin with a 12-inch outlet pipe across the

southwest corner of the driveway on Lot 7. Part of this gulch also runs in very close

proximity to the base of the retaining wall supporting the proposed driveway and turnout

on Lot 7.

LKP Engineering, Inc. -1-

DRAINAGE STUDY

RECORDS RESEARCH

For the drainage study we used the following resources:

1. Topographic survey, e-mailed by Lee Lechner, registered land surveyor.

2. Site plan, emailed by Stephanie Lord-Johnson LEED AP, with Berglund

Architects, LLC.

3. NOAA Atlas 2, Volume III-Colorado, for the rainfall intensities in the

Western United States.

4. Rainfall intensity-duration-frequency curves for the Edwards area.

5. Soil Survey of the Aspen-Gypsum Area of Garfield County from the US

Department of Agriculture Soil Conservation Service.

6. USDA NRCS, TR55 Software

7. Rational Method Calculations

8. Manning’s Open Channel and Pipe Flow Calculator

9. Partial field site reconnaissance (September 18, October 31, and November 2,

2014).

10. Eagle County GIS Department topography.

DRAINAGE BASIN

The proposed development is within the Eagle River Drainage basin. The

watershed area for Deadhorse Gulch is approximately 138 acres. The watershed is in a

plume shape with a maximum elevation of 8410 feet above sea level and 7386 feet above

sea level at the discharge point. The Deadhorse Gulch had water running in it during our

site visits, and appears to be a live, mountain stream. At the time of our visit, the gulch

ditch had 2-4 inches of water depth. The section that we walked, was about 600 feet

above the outlet, and within this area, the stream channel had irregular width ranging

from one to four feet, waterfalls and pools, and it was winding through the juniper forest.

The ditch channel was for the most part rectangular with 12-inch sides, while the banks

had variable heights and slopes, with an average of one to one side slope. Vegetation

cover of the drainage basin consists of juniper forest with sage brush on the open areas,

and sparse grass. There was also a lot of rock over the area.

DRAINAGE CRITERIA

The USDA (United States Department of Agriculture) NRCS ( Natural Resources

Conservation Service) software WinTR-55 Small Watershed Hydrology was used for the


DRAINAGE STUDY

calculations of the watershed hydrology. The rational method, for small watersheds of up

to 200 acres, was used for the calculations of watershed for the drainage swale. The

design storm events analyzed were the 2, 10, 50, and 100-year storms.

FINDINGS AND RECOMMENDATIONS

The Win TR-55 software was used to calculate the flow from the Deadhorse

Gulch Watershed.

Following is the Watershed Peak Flow Table (the full report is attached):

Project: 14-2953

645 Beard Creek Trail

Eagle County, Colorado

Watershed Peak Table

Sub-Area Peak Flow by Rainfall Return Period

or Reach 2-Yr 10-Yr 50-Yr 100-Yr

Identifier (cfs) (cfs) (cfs) (cfs)

----------------------------------------------------------------------------------

SUBAREAS

Tract 1 2.22 33.04 94.69 129.27

REACHES

OUTLET 2.22 33.04 94.69 129.27

Based on this study and the condition of the watershed at present time, the peak

flow from a 100-year storm event is 129 cfs.

The existing 30-inch culvert was corrugated plastic pipe with smooth inner walls.

Based on the survey information by lee Lechner, the pipe is 119 feet long and it has a

slope of 15.2%. The capacity of the existing 30-inch culvert was calculated based on the

Manning’s Pipe Formula. Following are the calculations:


DRAINAGE STUDY

Existing 30-inch Culvert

CPP with Smooth Inner Wall

INPUT DATA:

Pipe diameter D: 2.5 ft

Flow depth y: 2.4 ft

Bottom slope S: 0.152 ft/ft

Manning's n: 0.012

INTERMEDIATE CALCS:

Constant k: 1.486

Flow area A: 4.842 ft2

Wetted perimeter P: 6.847 ft

Hydraulic radius R: 0.707 ft

Relative depth y/D: 0.960

Froude number [based on y]: 4.361

OUTPUT:

Discharge Q: 185.6 cfs

Flow velocity V: 38.32 fps

Based on the above calculations, the peak flow from the watershed is 129 cfs and

the capacity of the existing 30-inch culvert is 186 cfs. The existing culvert, for the

present time and conditions, has a sufficient capacity to transmit the 100-year peak flow

from the Deadhorse Gulch watershed.

With the proposed development on the lot, a driveway crossing is proposed over

the Deadhorse channel. On the architectural site/grading plan they show about 40-foot

extension to the existing 30-inch culvert for this purpose.

At the inlet of the culvert extension, we recommend an end section with a trash

rack to prevent debris and rocks from blocking the culvert. We also recommend that a

new storm manhole with an inlet grate and steps for maintenance be constructed at the

junction of the existing culvert with the proposed new culvert. The construction of the

culvert will serve the purpose for future maintenance of the culvert and as an inlet for the

runoff from the proposed new driveway. At the base of the driveway we also recommend

a 4-foot concrete pan with a two-inch depth. The concrete pan will extend from the base

of the driveway to the inlet at the proposed new, storm manhole.


DRAINAGE STUDY

Drainage above the Proposed Residence

The watershed above the proposed drainage swale is 1.72 acres. The peak flow

for the 100-year storm event for the watershed of the proposed drainage swale was

calculated by the Rational method:

Q=CiA

Where:

Q = Peak Discharge (cfs)

C = Runoff coefficient, a ration of runoff to rainfall

I = Average rainfall intensity for a duration equal to the time of concentration, for

a selected return period (in/hr)

A = Watershed drainage area (ac)

The appended rainfall intensity curves for Edwards, Eagle County, were used in

the calculations. Runoff coefficient of 0.5 was used in the calculations for a steep

watershed with sage brush and juniper type of vegetation cover.

Following are the summary results for the 100-year storm event:

Watershed above the Diversion Drainage Swale

INPUT DATA:

Runoff coefficient C : .05

Rainfall intensity I : 5.3 in hr-1

Drainage area A : 1.72 ac

OUTPUT:

Peak discharge Qp : 4.60 cfs

Based on the peak discharge of 4.6 cfs a drainage swale cross section was

calculated with a 1-foot bottom, 1H:1V slope sides and two feet total depth. The swale

will be lined with a pond liner and rock. The purpose of the drainage swale is to divert

the uphill runoff and to protect the proposed residence. The backfill material and the

bottom of the swale will be compacted before the placement of the pond liner and the

rocks, and the disturbed surrounding areas will be re-vegetated to reduce the potential for

erosion. In addition to the construction of the proposed drainage swale, the two dry


DRAINAGE STUDY

gulches in the northeast corner of the lot will be incorporated into the drainage swale and

any parts of the dry gulches remaining below the swale will be filled in and revegetated.

Watershed above the existing dry gulch and 12-inch culvert on the east side

of the property. Drainage study of this watershed is not part of our scope of work. The

dry gulch does not originate or discharge on Lot 8. The existing dry gulch and the

structures below were not evaluated. We understand that erosion of the channel is an

ongoing event. In order to reduce the erosion of the natural, drainage channel, we

propose (see the drainage plan) that the dry gulch be reconstructed with a pond liner and

lined with rip-rap. In addition, and this is at the discretion of the homeowner, we

recommend a concrete apron around the existing catch basin inlet, which will also reduce

the potential of erosion around the inlet and guide the water toward it. The above

recommendations are standard practice for erosion control and can and should be

evaluated by the consultant for Lot 7.

Maintenance

For the continuous performance of the proposed drainage improvements to the

site a regular maintenance must be scheduled. As a minimum, in spring and fall the inlet

to the 30-inch culvert and the manhole inlet grate must be inspected and cleaned as

necessary. Additional maintenance after heavy storms should be done as well. At the

same time the drainage swales should be observed and cleaned from debris and sediment.

LIMITATIONS

The above report has been prepared for the exclusive use of the Lisa and Robert

Myers for the development their property at 645 Beard Creek Trail in the Cordillera

Valley Club, Eagle County, Colorado. The study is limited to the information provided

and the data available at the time of our study.

This report has been prepared according to locally accepted professional

engineering standards at this time. There is no other warranty either expressed or

implied.

If you have any questions, please do not hesitate to call.

Sincerely,


Luiza Petrovska, PE

EnclosureC:\Users\Luiza\Documents\_WPX4\14-2953Myers\14-2953dr_st.wpd


DRAINAGE STUDY

APPENDIX A


WinTR-55 Current Data Description

--- Identification Data ---

User: LP Date: 11/4/2014Project: 14-2953 Units: EnglishSubTitle: 645 Beard CReek Trail Areal Units: AcresState: ColoradoCounty: EagleFilename: C:\Users\Luiza\Documents\_WPX4\14-2953Myers\tr55study.w55

--- Sub-Area Data ---

Name Description Reach Area(ac) RCN Tc------------------------------------------------------------------------------Tract 1 Existing Land Use Outlet 138 73 .159

Total area: 138 (ac)

--- Storm Data --

Rainfall Depth by Rainfall Return Period

2-Yr 5-Yr 10-Yr 25-Yr 50-Yr 100-Yr 1-Yr (in) (in) (in) (in) (in) (in) (in)-------------------------------------------------------------------------------- 1.24 1.53 1.78 2.14 2.44 2.75 1.08

Storm Data Source: User-provided custom storm dataRainfall Distribution Type: Type IIDimensionless Unit Hydrograph: <standard>

WinTR-55, Version 1.00.10 Page 1 11/4/2014 12:23:41 PM

LP 14-2953 645 Beard CReek Trail Eagle County, Colorado

Storm Data

Rainfall Depth by Rainfall Return Period

2-Yr 5-Yr 10-Yr 25-Yr 50-Yr 100-Yr 1-Yr (in) (in) (in) (in) (in) (in) (in)-------------------------------------------------------------------------------- 1.24 1.53 1.78 2.14 2.44 2.75 1.08

Storm Data Source: User-provided custom storm dataRainfall Distribution Type: Type IIDimensionless Unit Hydrograph: <standard>



Watershed Peak Table

Sub-Area Peak Flow by Rainfall Return Period or Reach 2-Yr 10-Yr 50-Yr 100-YrIdentifier (cfs) (cfs) (cfs) (cfs)----------------------------------------------------------------------------------SUBAREASTract 1 2.22 33.04 94.69 129.27

REACHES

OUTLET 2.22 33.04 94.69 129.27



Hydrograph Peak/Peak Time Table

Sub-Area Peak Flow and Peak Time (hr) by Rainfall Return Period or Reach 2-Yr 10-Yr 50-Yr 100-YrIdentifier (cfs) (cfs) (cfs) (cfs) (hr) (hr) (hr) (hr)----------------------------------------------------------------------------------SUBAREASTract 1 2.22 33.04 94.69 129.27 12.10 12.04 12.03 12.02

REACHES

OUTLET 2.22 33.04 94.69 129.27



Sub-Area Summary Table

Sub-Area Drainage Time of Curve Receiving Sub-AreaIdentifier Area Concentration Number Reach Description (ac) (hr)--------------------------------------------------------------------------------Tract 1 138.00 0.159 73 Outlet Existing Land Use

Total Area: 138 (ac)



Sub-Area Time of Concentration Details

Sub-Area Flow Mannings's End Wetted TravelIdentifier/ Length Slope n Area Perimeter Velocity Time (ft) (ft/ft) (sq ft) (ft) (ft/sec) (hr)--------------------------------------------------------------------------------Tract 1 SHEET 90 0.0500 0.011 0.021 SHALLOW 1532 0.2600 0.050 0.052 CHANNEL 2151 0.1162 0.030 3.00 4.83 12.448 0.048 CHANNEL 2246 0.2048 0.030 3.00 4.83 16.418 0.038

Time of Concentration .159 ========



Sub-Area Land Use and Curve Number Details

Sub-Area Hydrologic Sub-Area CurveIdentifier Land Use Soil Area Number Group (ac)--------------------------------------------------------------------------------Tract 1 Pinyon - juniper (fair) D 31.5 80 Desert shrub (fair) A 9.5 55 Desert shrub (fair) B 97 72

Total Area / Weighted Curve Number 138 73 === ==


NOAA Atlas 14, Volume 8, Version 2 Location name: Edwards, Colorado, US* Latitude: 39.6730°, Longitude: -106.6000°

Elevation: 8384 ft* * source: Google Maps

POINT PRECIPITATION FREQUENCY ESTIMATES

Sanja Perica, Deborah Martin, Sandra Pavlovic, Ishani Roy, Michael St. Laurent, Carl Trypaluk, Dale Unruh, Michael Yekta, Geoffery Bonnin

NOAA, National Weather Service, Silver Spring, Maryland

PF_tabular | PF_graphical | Maps_&_aerials

PF tabularPDS-based point precipitation frequency estimates with 90% confidence intervals (in inches)1

DurationAverage recurrence interval (years)

1 2 5 10 25 50 100 200 500 1000

5-min 0.111(0.088-0.142)

0.173(0.137-0.222)

0.271(0.212-0.348)

0.347(0.271-0.449)

0.447(0.332-0.597)

0.520(0.378-0.709)

0.588(0.413-0.829)

0.653(0.439-0.956)

0.734(0.474-1.11)

0.789(0.500-1.23)

10-min 0.163(0.128-0.208)

0.254(0.200-0.325)

0.396(0.311-0.509)

0.509(0.397-0.657)

0.655(0.486-0.874)

0.761(0.553-1.04)

0.861(0.605-1.21)

0.957(0.643-1.40)

1.07(0.693-1.63)

1.16(0.732-1.81)

15-min 0.199(0.157-0.254)

0.309(0.244-0.396)

0.483(0.379-0.621)

0.620(0.484-0.802)

0.799(0.593-1.07)

0.928(0.675-1.27)

1.05(0.737-1.48)

1.17(0.784-1.71)

1.31(0.846-1.99)

1.41(0.892-2.20)

30-min 0.293(0.231-0.374)

0.399(0.314-0.511)

0.575(0.451-0.739)

0.723(0.564-0.934)

0.929(0.697-1.26)

1.09(0.798-1.50)

1.25(0.885-1.79)

1.42(0.960-2.10)

1.64(1.07-2.52)

1.81(1.15-2.84)

60-min 0.387(0.305-0.495)

0.486(0.383-0.622)

0.655(0.514-0.841)

0.803(0.626-1.04)

1.02(0.770-1.39)

1.19(0.878-1.66)

1.38(0.976-1.97)

1.57(1.07-2.33)

1.84(1.20-2.83)

2.05(1.30-3.20)

2-hr 0.482(0.383-0.611)

0.572(0.455-0.726)

0.735(0.581-0.935)

0.883(0.695-1.13)

1.11(0.849-1.51)

1.30(0.966-1.79)

1.50(1.08-2.14)

1.72(1.18-2.53)

2.03(1.34-3.10)

2.29(1.46-3.53)

3-hr 0.553(0.442-0.697)

0.634(0.506-0.800)

0.784(0.623-0.993)

0.924(0.731-1.18)

1.14(0.882-1.55)

1.33(0.997-1.82)

1.53(1.11-2.17)

1.75(1.21-2.57)

2.07(1.38-3.14)

2.33(1.50-3.57)

6-hr 0.695(0.560-0.869)

0.781(0.628-0.977)

0.938(0.752-1.18)

1.08(0.863-1.37)

1.31(1.02-1.74)

1.50(1.13-2.03)

1.70(1.24-2.38)

1.93(1.35-2.79)

2.25(1.51-3.37)

2.52(1.64-3.81)

12-hr 0.864(0.702-1.07)

0.992(0.805-1.23)

1.22(0.982-1.51)

1.41(1.14-1.77)

1.70(1.33-2.23)

1.94(1.48-2.59)

2.19(1.61-3.01)

2.45(1.73-3.49)

2.83(1.91-4.16)

3.12(2.05-4.66)

24-hr 1.08(0.882-1.32)

1.24(1.02-1.53)

1.53(1.25-1.88)

1.78(1.44-2.20)

2.14(1.69-2.78)

2.44(1.87-3.22)

2.75(2.04-3.73)

3.08(2.19-4.32)

3.53(2.41-5.13)

3.89(2.58-5.74)

2-day 1.34(1.11-1.63)

1.52(1.26-1.85)

1.84(1.51-2.24)

2.12(1.73-2.60)

2.53(2.02-3.26)

2.88(2.24-3.76)

3.25(2.43-4.37)

3.64(2.62-5.06)

4.19(2.90-6.02)

4.64(3.11-6.75)

3-day 1.52(1.26-1.84)

1.73(1.43-2.09)

2.09(1.73-2.54)

2.42(1.98-2.95)

2.89(2.31-3.69)

3.28(2.55-4.25)

3.68(2.78-4.92)

4.12(2.98-5.68)

4.73(3.29-6.73)

5.21(3.52-7.52)

4-day 1.67(1.39-2.02)

1.91(1.59-2.30)

2.31(1.91-2.79)

2.66(2.19-3.23)

3.17(2.54-4.02)

3.59(2.81-4.63)

4.02(3.04-5.34)

4.49(3.25-6.15)

5.13(3.58-7.25)

5.64(3.82-8.09)

7-day 2.09(1.75-2.49)

2.34(1.96-2.80)

2.78(2.32-3.34)

3.17(2.63-3.82)

3.73(3.01-4.69)

4.19(3.30-5.35)

4.67(3.56-6.13)

5.18(3.79-7.02)

5.88(4.14-8.23)

6.44(4.41-9.15)

10-day 2.44(2.06-2.90)

2.71(2.28-3.23)

3.18(2.67-3.80)

3.59(3.00-4.31)

4.20(3.41-5.25)

4.69(3.72-5.96)

5.21(3.99-6.80)

5.76(4.24-7.76)

6.53(4.62-9.07)

7.13(4.91-10.1)

20-day 3.41(2.90-4.02)

3.77(3.20-4.44)

4.38(3.70-5.17)

4.91(4.13-5.83)

5.68(4.65-7.01)

6.31(5.04-7.91)

6.96(5.38-8.97)

7.65(5.68-10.2)

8.61(6.16-11.8)

9.36(6.52-13.0)

30-day 4.25(3.62-4.97)

4.70(4.01-5.51)

5.46(4.64-6.42)

6.12(5.17-7.22)

7.04(5.78-8.61)

7.78(6.25-9.67)

8.54(6.63-10.9)

9.32(6.96-12.3)

10.4(7.48-14.1)

11.2(7.87-15.5)

45-day 5.35(4.59-6.23)

5.95(5.10-6.94)

6.94(5.93-8.11)

7.75(6.59-9.10)

8.87(7.30-10.7)

9.74(7.85-12.0)

10.6(8.27-13.4)

11.5(8.61-14.9)

12.6(9.13-17.0)

13.5(9.53-18.5)

60-day 6.34(5.46-7.35)

7.08(6.09-8.22)

8.26(7.09-9.62)

9.22(7.87-10.8)

10.5(8.66-12.6)

11.5(9.26-14.0)

12.4(9.70-15.5)

13.3(10.0-17.2)

14.5(10.5-19.3)

15.4(10.9-20.9)

1 Precipitation frequency (PF) estimates in this table are based on frequency analysis of partial duration series (PDS).Numbers in parenthesis are PF estimates at lower and upper bounds of the 90% confidence interval. The probability that precipitation frequency estimates (for a given duration and average recurrence interval) will be greater than the upper bound (or less than the lower bound) is 5%. Estimates at upper bounds are not checked against probable maximum precipitation (PMP) estimates and may be higher than currently valid PMP values.Please refer to NOAA Atlas 14 document for more information.

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PF graphical

Page 1 of 4Precipitation Frequency Data Server

11/4/2014http://hdsc.nws.noaa.gov/hdsc/pfds/pfds_printpage.html?lat=39.6730&lon=-106.6000&dat...

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US Department of CommerceNational Oceanic and Atmospheric Administration

National Weather ServiceOffice of Hydrologic Development

1325 East West HighwaySilver Spring, MD 20910



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