HomeMy WebLinkAboutElk Meadows Drainage Memorandum.pdfMay 22, 2014
Mr. Tom Kassmel
Town of Vail, Department of Public Works
75 S. Frontage Road
Vail, Colorado 81657
Re: Elk Meadows Subdivision: Drainage Analysis (Rev. 1)
Martin/Martin, Inc. Project No.:13.0874
Mr. Kassmel:
This letter is intended to replace the letter dated May 15, 2014 for the same project.
Martin/Martin, Inc. has completed a review of the drainage basin tributary to the Elk Meadows Subdivision
in Vail, Colorado. The purpose of the analysis is to correctly size the proposed driveway culverts associated
with the new single-family homes to be constructed on Lots 1, 2, and 3.
Based on a site visit, coupled with a review of aerial imagery and USGS topographical information, it was
determined that the basin is approximately 145 acres in area and estimated to be 2.3% impervious. A map
identifying the basin limits is attached to this letter.
The Rational Method was utilized to analyze the runoff from the basin. It was determined that the 100-year
flow rate toward Lot 1 and the proposed culvert is an estimated 173 CFS. Per our previous discussion, it is
permissible for the 100-year flow rate to be conveyed across the private, shared drive and the storm system
shall accommodate the 25-year flow rate for the basin, which is an estimated 96 CFS. A 30-inch smooth-
walled pipe at 2.8% slope can convey approximately 81 CFS. An 18-inch reinforced concrete pipe at 2.7%
slope can convey approximately 17 CFS. Therefore, between the 18-inch culverts north of the drive and the
30-inch culvert south of the drive, the 25-year storm event is designed to be conveyed below-grade.
The proposed area inlet west of Lot 1 is intended to intercept nuisance flows from the hill side south and
southeast of Lot 1. Flows exceeding the capacity of the inlet will be conveyed over the turnaround and
along historic paths to the west.
Two cross sections for the shared, private drive were evaluated to identify the limits of the flow path during
the 100-year storm event. The locations are along the east edge of the proposed driveways and were
selected as critical points relative to the homes on Lots 1 and 2. By the time the flow passes Lot 3, it should
have made its way south of the shared drive and into the existing swale.
The first cross section, taken at roadway station 11+65 yields an approximate water surface elevation of
8316.4 which is more than 6 inches below the proposed garage elevation of 8317.0 for the home on Lot 2.
06/23/14
Elk Meadows Subdivision, Lot 1: Drainage Analysis
May 15, 2014
P a g e 2 | 2
The second cross section, taken at roadway station 12+40 yields an approximate water surface elevation of
8321.1 which is also more than 6 inches below the proposed garage elevation of 8321.9 for the home on Lot
1.
In summary, the proposed storm system for the Elk Meadows Subdivision has been designed to pass the 96
CFS, 25-year storm event below-grade, through the culverts and convey the 173 CFS 100-year storm event
overland, along the private shared drive past the turnaround then back into the swale and along historic
drainage paths toward the west.
Refer to the attachments for corresponding calculations.
Let me know if you have any questions.
Sincerely,
L. Mark Luna, PE
Associate
[Attachments]
06/23/14
06/23/14
PROJECT INFORMATION
PROJECT NAME:
PROJECT NO:
DESIGN BY:
REVIEWED BY:
JURISDICTION:
REPORT TYPE:
DATE:
C2 C5 C25 C100 % IMPERV
0.04 0.15 0.37 0.50 0%
0.73 0.75 0.80 0.83 90%
0.89 0.90 0.94 0.96 100%
0.73 0.75 0.80 0.83 90%
145.00 0.06 0.17 0.38 0.51 2.3%
AREA
(ACRES) C2 C5 C10 C100
141.50 0.04 0.15 0.37 0.50 0%
1.00 0.73 0.75 0.80 0.83 90%
2.00 0.89 0.90 0.94 0.96 100%
0.50 0.73 0.75 0.80 0.83 90%
145.00 0.06 0.17 0.38 0.51 2.3%
145.00 0.06 0.17 0.38 0.51 2.3%
ASPHALT/CONCRETE
ROOF
LANDSCAPE
ELK MEADOWS SUBDIVISION
13.0874
J. YARNELL
L. M. LUNA
TOWN OF VAIL
N/A
05/14/14
JURISDICTIONAL STANDARD
DRIVES AND WALKS
SURFACE CHARACTERISTICS
COMPOSITE RUNOFF COEFFICIENTS PERCENT
IMPERVIOUSNESS
SUB-BASIN
TOTAL SITE COMPOSITE
ROOF
ASPHALT/CONCRETE
TOTAL SITE COMPOSITE
1
LANDSCAPE
DRIVES AND WALKS
SUB-BASIN COMPOSITE
6/3/2014 9:31 AM
COMPOSITE_C-VALUES
H:\13.0874-ELK MEADOWS SUBDIVISION\ENG\DRAINAGE\Rational Method - Proposed.xlsm
06/23/14
CALCULATED BY:
JOB NO:
CHECKED BY:
PROJECT:
DATE:
FINAL
tc
AREA LENGTH SLOPE ti LENGTH SLOPE VEL. tt COMP. TOT. LENGTH
ac ft ft/ft min ft ft/ft fps Min tc
ft min min
(1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14) (15)
1 1 0.17 145.00 250 0.1000 12.4 5000 0.1000 5 1.58 52.7 65.1 5250.0 39.2 39.2
*Velocity (V) = CvSw0.5
TABLE RO-2
*Table RO-2, UDFCD (V.1), Chapter 5, Page RO-6
in which: Cv = Conveyance Coefficient (See Table Above)
Sw = Watercourse Slope (ft/ft)
BASIN
DESIGN
POINT
C5
tc=(L/180)+10 Cv
Nearly Bare Ground 10
Grassed Waterway 15
Paved Areas and Shallow Paved Swales 20
Heavy Meadow 2.5
Tillage / Field 5
Short Pasture and Lawns 7
Type of Land Surface Conveyance Coefficient, Cv
tc CHECK
REMARKS
J. YARNELL
L. M. LUNA
05/14/14
DATA
SUB-BASIN
TIME (ti)
INITIAL/OVERLAND TRAVEL TIME
TIME OF CONCENTRATION SUMMARY
13.0874
ELK MEADOWS SUBDIVISIO
STANDARD FORM SF-2
(RATIONAL METHOD PROCEDURE)
(tt) (URBANIZED BASINS)
TOC
5/21/2014 3:17 PM
H:\13.0874-ELK MEADOWS SUBDIVISION\ENG\DRAINAGE\Rational Method - Proposed.xlsm
06/23/14
CALCULATED BY: J. YARNELL
JOB NO: 13.0874
CHECKED BY: L. M. LUNA
PROJECT: ELK MEADOWS SUBDIVISI
DATE: 05/14/14
DESIGN STORM: 25-YEAR
ONE-HR PRECIP: 1.3
(1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13)
1 1 145.00 0.38 39.2 55.10 1.73 95.56
I. One-Hr Precipitation Values for Eagle County
Return Period: 2-YEAR 5-YEAR 25-YEAR 100-YEAR
Depth In Inches: 0.60 0.90 1.30 1.75
*Equation RA-3, UDFCD (V.1), Chapter 4, Page RA-6
*Rainfall Intensity: In Which: I = Rainfall Intensity (Inches Per Hour)
P1 = 1-Hour Point Rainfall Depth (Inches)
tc = Time Of Concentration (Minutes)
REMARKS
AREA
(AC)
RUNOFF
COEFF
tc
(MIN)
BASIN DESIGN POINT
DIRECT RUNOFF TOTAL RUNOFF
tc
(MIN)
S(CxA)
(AC)
I
(IN/HR)
Q
(CFS)
STANDARD FORM SF-3
STORM DRAINAGE SYSTEM DESIGN
(RATIONAL METHOD PROCEDURE)
CxA
(AC)
I
(IN/HR)
Q
(CFS)
25-YEAR
5/21/2014 3:17 PM
H:\13.0874-ELK MEADOWS SUBDIVISION\ENG\DRAINAGE\Rational Method - Proposed.xlsm
06/23/14
CALCULATED BY: J. YARNELL
JOB NO: 13.0874
CHECKED BY: L. M. LUNA
PROJECT: ELK MEADOWS SUBDIVISI
DATE: 05/14/14
DESIGN STORM: 100-YEAR
ONE-HR PRECIP: 1.75
(1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13)
1 1 145.00 0.51 39.2 73.95 2.33 172.65
I. One-Hr Precipitation Values for Eagle County
Return Period: 2-YEAR 5-YEAR 25-YEAR 100-YEAR
Depth In Inches: 0.60 0.90 1.30 1.75
*Equation RA-3, UDFCD (V.1), Chapter 4, Page RA-6
*Rainfall Intensity: In Which: I = Rainfall Intensity (Inches Per Hour)
P1 = 1-Hour Point Rainfall Depth (Inches)
tc = Time Of Concentration (Minutes)
REMARKS
AREA
(AC)
RUNOFF
COEFF
tc
(MIN)
STANDARD FORM SF-3
STORM DRAINAGE SYSTEM DESIGN
(RATIONAL METHOD PROCEDURE)
CxA
(AC)
I
(IN/HR)
Q
(CFS)
BASIN DESIGN POINT
DIRECT RUNOFF TOTAL RUNOFF
tc
(MIN)
S(CxA)
(AC)
I
(IN/HR)
Q
(CFS)
100-YEAR
5/21/2014 3:17 PM
H:\13.0874-ELK MEADOWS SUBDIVISION\ENG\DRAINAGE\Rational Method - Proposed.xlsm
06/23/14
Project Description
Friction Method Manning Formula
Solve For Discharge
Input Data
Roughness Coefficient 0.013
Channel Slope 0.02740 ft/ft
Normal Depth 1.50 ft
Diameter 1.50 ft
Results
Discharge 17.39 ft³/s
Flow Area 1.77 ft²
Wetted Perimeter 4.71 ft
Hydraulic Radius 0.38 ft
Top Width 0.00 ft
Critical Depth 1.44 ft
Percent Full 100.0 %
Critical Slope 0.02393 ft/ft
Velocity 9.84 ft/s
Velocity Head 1.50 ft
Specific Energy 3.00 ft
Froude Number 0.00
Maximum Discharge 18.70 ft³/s
Discharge Full 17.39 ft³/s
Slope Full 0.02740 ft/ft
Flow Type SubCritical
GVF Input Data
Downstream Depth 0.00 ft
Length 0.00 ft
Number Of Steps 0
GVF Output Data
Upstream Depth 0.00 ft
Profile Description
Profile Headloss 0.00 ft
Average End Depth Over Rise 0.00 %
Normal Depth Over Rise 100.00 %
Downstream Velocity Infinity ft/s
18-inch RCP @ 2.74%
5/14/2014 2:15:13 PM
Bentley Systems, Inc. Haestad Methods Solution CenterBentley FlowMaster V8i (SELECTseries 1) [08.11.01.03]
27 Siemons Company Drive Suite 200 W Watertown, CT 06795 USA +1-203-755-1666 2
of 1 Page
06/23/14
GVF Output Data
Upstream Velocity Infinity ft/s
Normal Depth 1.50 ft
Critical Depth 1.44 ft
Channel Slope 0.02740 ft/ft
Critical Slope 0.02393 ft/ft
18-inch RCP @ 2.74%
5/14/2014 2:15:13 PM
Bentley Systems, Inc. Haestad Methods Solution CenterBentley FlowMaster V8i (SELECTseries 1) [08.11.01.03]
27 Siemons Company Drive Suite 200 W Watertown, CT 06795 USA +1-203-755-1666 2
of 2 Page
06/23/14
Project Description
Friction Method Manning Formula
Solve For Full Flow Capacity
Input Data
Roughness Coefficient 0.011
Channel Slope 0.02800 ft/ft
Normal Depth 2.50 ft
Diameter 2.50 ft
Discharge 81.11 ft³/s
Results
Discharge 81.11 ft³/s
Normal Depth 2.50 ft
Flow Area 4.91 ft²
Wetted Perimeter 7.85 ft
Hydraulic Radius 0.63 ft
Top Width 0.00 ft
Critical Depth 2.47 ft
Percent Full 100.0 %
Critical Slope 0.02550 ft/ft
Velocity 16.52 ft/s
Velocity Head 4.24 ft
Specific Energy 6.74 ft
Froude Number 0.00
Maximum Discharge 87.25 ft³/s
Discharge Full 81.11 ft³/s
Slope Full 0.02800 ft/ft
Flow Type SubCritical
GVF Input Data
Downstream Depth 0.00 ft
Length 0.00 ft
Number Of Steps 0
GVF Output Data
Upstream Depth 0.00 ft
Profile Description
Profile Headloss 0.00 ft
Average End Depth Over Rise 0.00 %
30" Culvert
5/22/2014 3:11:42 PM
Bentley Systems, Inc. Haestad Methods Solution CenterBentley FlowMaster V8i (SELECTseries 1) [08.11.01.03]
27 Siemons Company Drive Suite 200 W Watertown, CT 06795 USA +1-203-755-1666 2
of 1 Page
06/23/14
GVF Output Data
Normal Depth Over Rise 100.00 %
Downstream Velocity Infinity ft/s
Upstream Velocity Infinity ft/s
Normal Depth 2.50 ft
Critical Depth 2.47 ft
Channel Slope 0.02800 ft/ft
Critical Slope 0.02550 ft/ft
30" Culvert
5/22/2014 3:11:42 PM
Bentley Systems, Inc. Haestad Methods Solution CenterBentley FlowMaster V8i (SELECTseries 1) [08.11.01.03]
27 Siemons Company Drive Suite 200 W Watertown, CT 06795 USA +1-203-755-1666 2
of 2 Page
06/23/14
Project Description
Friction Method Manning Formula
Solve For Normal Depth
Input Data
Channel Slope 0.06200 ft/ft
Discharge 77.09 ft³/s
Section Definitions
Station (ft) Elevation (ft)
0+00 17.00
0+32 16.32
0+50 16.00
0+82 16.69
Roughness Segment Definitions
Start Station Ending Station Roughness Coefficient
(0+00, 17.00) (0+82, 16.69) 0.013
Options
Current Roughness Weighted
Method
Pavlovskii's Method
Open Channel Weighting Method Pavlovskii's Method
Closed Channel Weighting Method Pavlovskii's Method
Results
Normal Depth 0.39 ft
Elevation Range 16.00 to 17.00 ft
Flow Area 7.93 ft²
Wetted Perimeter 39.74 ft
Hydraulic Radius 0.20 ft
Top Width 39.73 ft
Normal Depth 0.39 ft
Critical Depth 0.68 ft
Critical Slope 0.00350 ft/ft
Section Sta 11+65
5/22/2014 3:23:25 PM
Bentley Systems, Inc. Haestad Methods Solution CenterBentley FlowMaster V8i (SELECTseries 1) [08.11.01.03]
27 Siemons Company Drive Suite 200 W Watertown, CT 06795 USA +1-203-755-1666 2
of 1 Page
06/23/14
Results
Velocity 9.72 ft/s
Velocity Head 1.47 ft
Specific Energy 1.86 ft
Froude Number 3.84
Flow Type Supercritical
GVF Input Data
Downstream Depth 0.00 ft
Length 0.00 ft
Number Of Steps 0
GVF Output Data
Upstream Depth 0.00 ft
Profile Description
Profile Headloss 0.00 ft
Downstream Velocity Infinity ft/s
Upstream Velocity Infinity ft/s
Normal Depth 0.39 ft
Critical Depth 0.68 ft
Channel Slope 0.06200 ft/ft
Critical Slope 0.00350 ft/ft
Section Sta 11+65
5/22/2014 3:23:25 PM
Bentley Systems, Inc. Haestad Methods Solution CenterBentley FlowMaster V8i (SELECTseries 1) [08.11.01.03]
27 Siemons Company Drive Suite 200 W Watertown, CT 06795 USA +1-203-755-1666 2
of 2 Page
06/23/14
Project Description
Friction Method Manning Formula
Solve For Normal Depth
Input Data
Channel Slope 0.06200 ft/ft
Discharge 77.09 ft³/s
Section Definitions
Station (ft) Elevation (ft)
0+00 21.80
0+32 21.00
0+50 20.60
0+80 21.92
Roughness Segment Definitions
Start Station Ending Station Roughness Coefficient
(0+00, 21.80) (0+80, 21.92) 0.013
Options
Current Roughness Weighted
Method
Pavlovskii's Method
Open Channel Weighting Method Pavlovskii's Method
Closed Channel Weighting Method Pavlovskii's Method
Results
Normal Depth 0.46 ft
Elevation Range 20.60 to 21.92 ft
Flow Area 7.17 ft²
Wetted Perimeter 30.90 ft
Hydraulic Radius 0.23 ft
Top Width 30.88 ft
Normal Depth 0.46 ft
Critical Depth 0.80 ft
Critical Slope 0.00332 ft/ft
Section Sta 12+40
5/22/2014 3:28:18 PM
Bentley Systems, Inc. Haestad Methods Solution CenterBentley FlowMaster V8i (SELECTseries 1) [08.11.01.03]
27 Siemons Company Drive Suite 200 W Watertown, CT 06795 USA +1-203-755-1666 2
of 1 Page
06/23/14
Results
Velocity 10.75 ft/s
Velocity Head 1.80 ft
Specific Energy 2.26 ft
Froude Number 3.93
Flow Type Supercritical
GVF Input Data
Downstream Depth 0.00 ft
Length 0.00 ft
Number Of Steps 0
GVF Output Data
Upstream Depth 0.00 ft
Profile Description
Profile Headloss 0.00 ft
Downstream Velocity Infinity ft/s
Upstream Velocity Infinity ft/s
Normal Depth 0.46 ft
Critical Depth 0.80 ft
Channel Slope 0.06200 ft/ft
Critical Slope 0.00332 ft/ft
Section Sta 12+40
5/22/2014 3:28:18 PM
Bentley Systems, Inc. Haestad Methods Solution CenterBentley FlowMaster V8i (SELECTseries 1) [08.11.01.03]
27 Siemons Company Drive Suite 200 W Watertown, CT 06795 USA +1-203-755-1666 2
of 2 Page
06/23/14