The URL can be used to link to this page

Home My WebLink AboutWS CAT, Stormwater Plan , Sheet (2) V1Page 1 221182 WESTERN STATES CAT TRUCK SHOP PARKING LOT EXPANSION Storm Drainage Design Narrative These calculations have been performed according to the City of Meridian Design Standards. 1.1 Property Description This project is taking place on an existing site. It expands an existing parking lot at the Western States CAT Truck Shop, at 400 E. Overland Road, in Meridian Idaho. The existing parking area currently drains to the north, using a valley gutter to convey water into the Western States equipment yard where it infiltrates. The existing area to be converted to parking lot is currently a combination of landscaping and drive lane, being used as an exit from the truck shop. The existing stormwater that encounters the drive lane is conveyed down curb and gutter, and again sent into the Western States equipment yard. There are 4 roof drains that also drain into the existing area to be improved, conveying stormwater from the rooftop of the main Truck Shop Building. The new parking area stormwater design is intended to contain all stormwater produced in the improved area, conveying to a seepage bed to be constructed in the improvement area. The existing portion of the parking lot that conveys its stormwater to the equipment yard will remain as-is, in its existing configuration. Infiltration tests have not yet been performed, based on soil strata from surrounding areas and anticipated ground water elevations, a conservative infiltration rate of 1 in/hour has been used for seepage bed sizing. Infiltration testing will be performed after issuance of the CZC occurs, and there is sufficient space in the improvement area to increase the size of the seepage bed if necessary. 1.2 Stormwater System Description The proposed on-site stormwater system consists of two drainage basin areas both of which are conveyed to the same seepage bed. The seepage bed has been designed for a 100-year storm event. The water in drainage basin 1 will be conveyed to 2 drop inlets and discharged into the seepage bed using a perforated pipe. The water from drainage basin 2 will be conveyed to one drop inlet and conveyed to the seepage bed. All conveyance occurs in 12” diameter storm pipe. The seepage bed will be filled with drain rock with a void volume of 40%. See Appendix A – Stormwater Plan for delineation of the basins and description of the system. 12/27/21 A-2021-0223 Page 2 221182 1.3 Design Criteria The stormwater facilities were designed in accordance with the ACHD Policy Manual Section 8000 and Section 8200 relating to stormwater. See appendix B for calculations. The design criteria for this seepage beds are: ▪ Store 100-year storm event at a 1-hour duration ▪ Infiltrate the 90% storm in 48 hours ▪ Minimum cover of 1.5-feet, unless under roadway or sidewalk then the minimum cover is 1-foot ▪ Washed Drain Rock is 1.5-2 inches ▪ 1.5 -feet of ASTM C33 filter sand ▪ Sediment increase factor of 25% ▪ 3-feet minimum from groundwater 1.4 Calculations 1.4.1 Design Inputs ▪ Total acreage included in calculations is 0.97 acres. ▪ The runoff coefficient for the future building is 0.95 with a total area of 10,194 square feet. ▪ The runoff coefficient for concrete and asphalt is 0.90, with a total area of 32,663 square feet. ▪ The runoff coefficient for landscaping is 0.20, with a total area of 12,526 square feet. ▪ Time of concentration is 5 minutes. ▪ Sedimentation Increase Factor is 1.25 1.4.2 Summary of Calculations ▪ Seepage bed dimensions – 65’ X 25’ X 6’ ▪ Seepage bed storage volume – 3900 CF ▪ Storm drainpipe sized for 100-year event – 12” Diameter ▪ Sand and grease trap size sized for 25-year event See appendix B for calculations. 12/27/21 A-2021-0223 ROW ROW ROW ROW ROW ROW ROW ROW ROW ROW ROW ROW ROW ROW P/L P/L P/L P/L P/L P/L P/L P/L P/L P/L P/L P/L P/L P/L P/L P/L P/L P/L P/L P/L P/L P/L P/L P/L EP EP EP EP EP E P EP SAW SAW SAW SAW 12''SD> 12''SD> 12''SD> 65.00' 25.00' 12''SD> 12''SD< 12''SD< STORMWATER PLAN C-103 --- --- 131 SW 5th Avenue, Suite A Meridian, Idaho 83642 (208) 288-1992 PROJECT NO. SHEET NO. 221182 DRAWN: CHECK: Page 3 221182 Appendix B: Stormwater Calculations Project: Client: Designer: Location: Date & Time: Flow, Q = CIA (cfs) Pre-Developed Runoff Coefficient, Cpre = 0.00 Developed Runoff Coefficient, Cw = 0.74 Storm Event = 100 year Total Area, A = 0.97 acres Time of Concentration, tc = 5 min Infiltration Area, Ai = 1,625 sqft Available Facility Volume, Va = 3900 cuft Infiltration Rate, Ir = 1 in/hour = 0.0014 ft/min Infiltrated Flow Rate, Qi = Ai x Ir = 2.3 cfm Offsite Historical Discharge Rate, Qd = Cpre x I x A (see table below) Maximum Flow, Qpeak = Cw x I x A - Qd (see table below) Pond Volume, V = Qpeak x t - Qi x (t + tc) - (Qd x t) (see table below) Sedimentation Increase Factor, fv = 1.15 Required Facility Volume, Vr = V x fv (see table below) Time to infiltrate, ti = (Vr / Qi) / 60 I V Vr hours minutes in/hr cfs cfm cfs cfm cf cf 0.08 5 4.38 0.00 0.0 3.14 188.6 921 1,059 0.17 10 3.16 0.00 0.0 2.27 136.1 1,327 1,526 0.25 15 2.57 0.00 0.0 1.84 110.7 1,615 1,857 0.33 20 2.17 0.00 0.0 1.56 93.5 1,813 2,085 0.50 30 1.73 0.00 0.0 1.24 74.5 2,156 2,480 0.67 40 1.47 0.00 0.0 1.06 63.3 2,431 2,795 0.83 50 1.24 0.00 0.0 0.89 53.4 2,546 2,928 1 60 1.06 0.00 0.0 0.76 45.7 2,592 2,981 2 120 0.61 0.00 0.0 0.44 26.3 2,870 3,301 3 180 0.45 0.00 0.0 0.32 19.4 3,071 3,532 4 240 0.36 0.00 0.0 0.26 15.5 3,168 3,643 5 300 0.30 0.00 0.0 0.22 12.9 3,188 3,666 6 360 0.26 0.00 0.0 0.19 11.2 3,207 3,688 8 480 0.21 0.00 0.0 0.15 9.0 3,247 3,734 <<<<< 10 600 0.17 0.00 0.0 0.12 7.3 3,027 3,482 12 720 0.15 0.00 0.0 0.11 6.5 3,015 3,467 18 1080 0.11 0.00 0.0 0.08 4.7 2,668 3,068 24 1440 0.08 0.00 0.0 0.06 3.6 1,886 2,169 Maximum Required Pond Volume, Vr = 3,734 cf < 3900 cf, VOLUME OK! Storm Duration Resulting in Max Volume = 8 hours Approximate Time to Infiltrate, ti = 27.6 hours = 1.1 days Truck Shop Parking Lot Expansion Western States CAT Centanni 131 S.W. 5TH Avenue, Suite A, Meridian, Idaho 83642 Meridian, ID Phone: 208.288.1992 - Fax: 208.288.1999 12/21/2021 10:57 IDF CURVE ZONE A - STORM WATER INFILTRATION FACILITY Duration, t Qd Qpeak 12/27/21 A-2021-0223 Page 4 221182 Project: Client: Designer: Description: Date: MAXIMUM RUNOFF AREA ALLOWABLE PER PIPE DIAMETER Qstorm = C*i*Aacres 1.49 0.464 n n Qstorm = C*i*Aacres Runoff Coefficient, C = 0.74 Manning's Coefficient, n = 0.011 Storm Event = 100 year Time of Concentration, tc = 5 minutes Rainfall Intensity, i = 3.81 in/hr Hydraulic Slope, S = 0.4 % Qpipe = Qstorm, solve for drainage area capacity based on pipe diameter Qpipe C*i Qpipe Apipe (sqft) (acres) 12 in 1.98 30568 0.70 12 in 15 in 3.06 47265 1.09 15 in 18 in 4.82 74418 1.71 18 in 21 in 6.50 100403 2.30 21 in 24 in 8.47 130859 3.00 24 in 30 in 15.36 237263 5.45 30 in PIPE SIZE DETERMINATION Basin/ Inlet Runoff Area Qpipe Vpipe (sf) (sf) (acres) (cfs) (fps) S 55,382 55,382 1.27 3.58 4.56 Cumulative Area Downstream Pipe Size (in) 12 in Upstream Basins Included Phone: 208.288.1992 - Fax: 208.288.1999 STORM DRAIN PIPE SIZING Truck Shop PL WS CAT Centanni Vpipe = Storm Pipe Qpipe = *Apipe*R2/3*S 1/2 = *D8/3*S1/2 Aacres = 131 S.W. 5TH Avenue, Suite A, Meridian, Idaho 83642 0.12 0.10 Pipe Dia., D (in) Qpipe (cfs) Serviceable Runoff Area Design Pipe Slope (%) 0.22 0.16 Pipe Dia., D (in) 0.15 0.10 TS 12/27/21 A-2021-0223 VERIFY SCALE: Scales based on 22"x34" prints. 1-1/2 Inches PAGE WESTERN STATES CAT TRUCK SHOP PARKING LOT EXPANSION NO. REVISIONS DATE This document or any part thereof in detail or design concept is the personal property of Keller Associates, Inc. and shall not be copied in any form without the written authorization of Keller Associates, Inc. PRELIMINARY Not For Construction 0 20 40 GENERAL SHEET NOTES SHEET KEYNOTES 01 25' X 65' X 6' SEEPAGE BED 02 12" STORM PIPE 03 STANDARD DROP INLET 04 12" PERFORATED PIPE 05 1000 GAL SAND AND GREASE TRAP 06 STORM CATCH MANHOLE 03 06 02 02 03 01 02 04 06 05 DRAINAGE BASIN 1 DRAINAGE BASIN 2 LEGEND APPENDIX A STORMWATER PLAN WESTERN STATES CAT TRUCK SHOP PARKING LOT EXPANSION EXISTING PARKING AREA - DRAINING TO EQUIPEMENT YARD NEW PARKING AREAS - DRAINING TO NEW SEEPAGE BED GB GB GB GB GB GB 12/27/21 A-2021-0223