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Home My WebLink AboutDRB140307_Lot 5 Drainage Memorandum_1406309400.pdf July 17, 2014 Mr. Tom Kassmel Town of Vail, Department of Public Works 75 S. Frontage Road Vail, Colorado 81657 Re: Elk Meadows Subdivision (Lot 5): Drainage Analysis Martin/Martin, Inc. Project No.:13.0874 Mr. Kassmel: 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 two-fold: 1. To correctly size the proposed driveway culvert associated with the new single-family home to be constructed on Lot 5; and 2. To verify the gulley’s capacity to convey the 100-year storm event south of the Lot without adversely impacting either Lot 5 or the existing residence south of Lot 5. Based on a site visit, coupled with a review of 1994 Town of Vail aerial topographical information, it appears that Buffehr Creek Road is crowned with a defined ditch along the north side. Therefore, the area tributary to the proposed driveway culvert is the southerly half of Buffehr Creek Road, the native grass slope between Buffehr Creek Road and Lot 5, and a portion of the roof for the new home to be constructed on Lot 5. It was determined that this basin is approximately 0.19 acres in area and estimated to be 41% impervious. The basin delineation is included on Sheet C3.5. The Rational Method was utilized to analyze the runoff from the basin. It was determined that the 100-year flow rate toward the proposed culvert beneath the driveway connection to Lot 5 is an estimated 0.8 CFS. An 18-inch reinforced concrete pipe at 10.9% slope can convey approximately 35 CFS. Therefore, the culvert is substantially over-sized but is the minimum size permitted per Town of Vail standards. Per the previous drainage analysis completed for Lots 1 and 3 (dated June 17, 2014), the 100-year flow rate through the gulley south of Lot 5 is estimated to be 173 CFS. One cross section through the gulley was evaluated to identify the resulting capacity after filling the north half of the gulley to construct the home on Lot 5. The narrowest corridor is at the southwest end of the retaining wall parallel to the southerly limit of Lot 5. As shown on the attached calculations, the resulting water surface elevation is estimated to be 8278.8 during the 100-year storm event. This is approximately one foot lower than the lowest surveyed existing grade along the north side of the existing home south of the gulley, and 10 feet below the proposed finished floor of the proposed home on Lot 5. In summary, the proposed driveway culvert for the Elk Meadows Subdivision Lot 5 has been designed to pass the 0.8 CFS, 100-year storm event below-grade. Additionally, the proposed fill within the existing Elk Meadows Subdivision, Lot 1: Drainage Analysis May 15, 2014 P a g e 2 | 2 gulley is not anticipated to result in flooding of either the existing residence south of the gulley or Lot 5 during the 173 CFS, 100-year storm event. 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% 0.19 0.38 0.45 0.59 0.68 40.6% AREA (ACRES) C2 C5 C10 C100 0.11 0.04 0.15 0.37 0.50 0% 0.01 0.73 0.75 0.80 0.83 90% 0.06 0.89 0.90 0.94 0.96 100% 0.00 0.73 0.75 0.80 0.83 90% 0.19 0.38 0.45 0.59 0.68 40.6% 0.19 0.38 0.45 0.59 0.68 40.6% SUB-BASIN COMPOSITE ROOF ASPHALT/CONCRETE TOTAL SITE COMPOSITE 1 LANDSCAPE DRIVES AND WALKS DRIVES AND WALKS SURFACE CHARACTERISTICS COMPOSITE RUNOFF COEFFICIENTS PERCENT IMPERVIOUSNESSSUB-BASIN TOTAL SITE COMPOSITE JURISDICTIONAL STANDARD ASPHALT/CONCRETE ROOF LANDSCAPE ELK MEADOWS SUBDIVISION 13.0874 J. YARNELL L. M. LUNA TOWN OF VAIL N/A 07/14/14 7/18/2014 8:03 AM COMPOSITE_C-VALUES H:\13.0874-ELK MEADOWS SUBDIVISION\ENG\DRAINAGE\Rational Method - Lot 5.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 0.45 0.19 58 0.2672 3.0 102 0.1225 7 2.45 0.7 3.7 160.0 10.9 5.0*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. LUNA07/14/14DATASUB-BASINTIME (ti)INITIAL/OVERLANDTRAVEL TIMETIME OF CONCENTRATION SUMMARY13.0874ELK MEADOWS SUBDIVISIONSTANDARD FORM SF-2(RATIONAL METHOD PROCEDURE)(tt)(URBANIZED BASINS)TOC7/18/2014 8:03 AMH:\13.0874-ELK MEADOWS SUBDIVISION\ENG\DRAINAGE\Rational Method - Lot 5.xlsm CALCULATED BY:J. YARNELLJOB NO:13.0874CHECKED BY:L. M. LUNAPROJECT:ELK MEADOWS SUBDIVISIONDATE:07/14/14DESIGN STORM:100-YEARONE-HR PRECIP:1.75(1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13)1 1 0.19 0.68 5.0 0.13 5.94 0.76I. 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-YEAR7/18/2014 8:03 AMH:\13.0874-ELK MEADOWS SUBDIVISION\ENG\DRAINAGE\Rational Method - Lot 5.xlsm Project Description Friction Method Manning Formula Solve For Discharge Input Data Roughness Coefficient 0.013 Channel Slope 0.10900 ft/ft Normal Depth 1.50 ft Diameter 1.50 ft Results Discharge 34.68 ft³/s Flow Area 1.77 ft² Wetted Perimeter 4.71 ft Hydraulic Radius 0.38 ft Top Width 0.00 ft Critical Depth 1.50 ft Percent Full 100.0 % Critical Slope 0.10454 ft/ft Velocity 19.62 ft/s Velocity Head 5.98 ft Specific Energy 7.48 ft Froude Number 0.00 Maximum Discharge 37.30 ft³/s Discharge Full 34.68 ft³/s Slope Full 0.10900 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" RCP @ 10.9% 7/18/2014 7:23:42 AM 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 1.50 ft Channel Slope 0.10900 ft/ft Critical Slope 0.10454 ft/ft 18" RCP @ 10.9% 7/18/2014 7:23:42 AM 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 0.07400 ft/ft Discharge 173.00 ft³/s Section Definitions Station (ft)Elevation (ft) 0+00 82.17 0+07 79.50 0+13 77.54 0+24 78.00 Roughness Segment Definitions Start Station Ending Station Roughness Coefficient (0+00, 82.17) (0+24, 78.00)0.030 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 1.30 ft Elevation Range 77.54 to 82.17 ft Flow Area 13.94 ft² Wetted Perimeter 15.77 ft Hydraulic Radius 0.88 ft Top Width 14.73 ft Normal Depth 1.30 ft Critical Depth 2.00 ft Critical Slope 0.01322 ft/ft Lot 5 Gulley Cross Section 7/18/2014 7:22:55 AM 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 12.41 ft/s Velocity Head 2.39 ft Specific Energy 3.69 ft Froude Number 2.25 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 1.30 ft Critical Depth 2.00 ft Channel Slope 0.07400 ft/ft Critical Slope 0.01322 ft/ft Lot 5 Gulley Cross Section 7/18/2014 7:22:55 AM 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