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Home My WebLink AboutElk Meadows Drainage Memorandum.pdf May 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. 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] 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 IMPERVIOUSNESSSUB-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 CALCULATED BY:JOB NO:CHECKED BY:PROJECT:DATE:FINALtcAREA LENGTH SLOPEtiLENGTH SLOPE VEL.ttCOMP.TOT. LENGTHac ft ft/ft min ft ft/ft fps Mintcft 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) = CvSw0.5TABLE RO-2*Table RO-2, UDFCD (V.1), Chapter 5, Page RO-6in which: Cv = Conveyance Coefficient (See Table Above)Sw = Watercourse Slope (ft/ft)BASINDESIGN POINTC5tc=(L/180)+10CvNearly Bare Ground10Grassed Waterway15Paved Areas and Shallow Paved Swales20Heavy Meadow2.5Tillage / Field5Short Pasture and Lawns7Type of Land SurfaceConveyance Coefficient, Cvtc CHECKREMARKSJ. YARNELLL. M. LUNA05/14/14DATASUB-BASINTIME (ti)INITIAL/OVERLANDTRAVEL TIMETIME OF CONCENTRATION SUMMARY13.0874ELK MEADOWS SUBDIVISIONSTANDARD FORM SF-2(RATIONAL METHOD PROCEDURE)(tt)(URBANIZED BASINS)TOC5/21/2014 3:17 PMH:\13.0874-ELK MEADOWS SUBDIVISION\ENG\DRAINAGE\Rational Method - Proposed.xlsm CALCULATED BY:J. YARNELLJOB NO:13.0874CHECKED BY:L. M. LUNAPROJECT:ELK MEADOWS SUBDIVISIONDATE:05/14/14DESIGN STORM:25-YEARONE-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 95.56I. One-Hr Precipitation Values for Eagle CountyReturn Period: 2-YEAR 5-YEAR 25-YEAR 100-YEARDepth 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)REMARKSAREA (AC)RUNOFF COEFFtc (MIN)BASIN DESIGN POINTDIRECT RUNOFFTOTAL RUNOFFtc (MIN)S(CxA) (AC)I (IN/HR)Q (CFS)STANDARD FORM SF-3STORM DRAINAGE SYSTEM DESIGN(RATIONAL METHOD PROCEDURE)CxA (AC)I (IN/HR)Q (CFS)25-YEAR5/21/2014 3:17 PMH:\13.0874-ELK MEADOWS SUBDIVISION\ENG\DRAINAGE\Rational Method - Proposed.xlsm CALCULATED BY:J. YARNELLJOB NO:13.0874CHECKED BY:L. M. LUNAPROJECT:ELK MEADOWS SUBDIVISIONDATE:05/14/14DESIGN STORM:100-YEARONE-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 2.33 172.65I. One-Hr Precipitation Values for Eagle CountyReturn Period: 2-YEAR 5-YEAR 25-YEAR 100-YEARDepth 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)REMARKSAREA (AC)RUNOFF COEFFtc (MIN)STANDARD FORM SF-3STORM DRAINAGE SYSTEM DESIGN(RATIONAL METHOD PROCEDURE)CxA (AC)I (IN/HR)Q (CFS)BASIN DESIGN POINTDIRECT RUNOFFTOTAL RUNOFFtc (MIN)S(CxA) (AC)I (IN/HR)Q (CFS)100-YEAR5/21/2014 3:17 PMH:\13.0874-ELK MEADOWS SUBDIVISION\ENG\DRAINAGE\Rational Method - Proposed.xlsm 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 2of1Page 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 2of2Page 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 2of1Page 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 2of2Page 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 2of1Page 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 2of2Page 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 2of1Page 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 2of2Page