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HomeMy WebLinkAboutDrainage ReportVILLAS AT AUTUMN ROAD AUTUMN RD, LITTLE ROCK, AR DRAINAGE REPORT FOR City of Little Rock, Pulaski County, AR JULY 2022 Owner & Developer: ICON HOMES, LLC Address: P.O. 23713 LITTLE ROCK, AR 72205 By: Narrative & Summary PROJECT TITLE VILLAS AT AUTUMN ROAD PROJECT PROPERTY OWNER ICON HOMES, LLC PROJECT LOCATION Autumn Rd, Little Rock, AR PROJECT DESCRIPTION The proposed development is a luxury single family project in Little Rock, AR. Total development site area is 4.97 acres. DRAINAGE ANALYSIS On Site Drainage- Rational method was used to determine the existing and proposed flows from proposed site. Detailed drainage calculations considering the future expected development has been conducted to determine the required detention pond and culvert dimensions. Summary of the calculations are below: Detention Pond • Pond is situated on the north side of the property. • Pre-development area : 5.02 acres. • Post-development area : 5.02 acres. • Pre-development runoff coefficient : 0.44. • Post-development runoff coefficient : 0.65. • Pond has a bottom area of 2000 SF with bottom elevation of 417.00’. • Pond is 4 ft deep and two 12'' RCP have been proposed for outflow structures. Peak flows for Pre and post development phase of onsite area have been tabulated below- Pre-development Post-dev. Without detention Post-dev. With detention Peak Flow (cfs) Peak Flow (cfs) Peak Flow (cfs) 2-Year 7.74 13.14 7.10 5-Year 8.53 14.54 7.64 10-Year 10.2 17.06 8.50 25-Year 11.74 19.56 9.64 CONCLUSION From the onsite drainage calculation, it is seen that there is decrease in flow for all storm events due to the proposed detention pond. CERTIFICATION I, William McFadden, Registered Professional Engineer No. 14048 in the State of Arkansas, hereby certify the drainage designs, and specifications contained in this report have been pre- pared in accordance with the regulations of the City of Little Rock, Arkansas, the Professional Engineers Registration Act of the State of Arkansas, and reflect the application of generally ac- cepted standard of engineering practice. I further certify that the improvements outlined in this report will not have any adverse effects to life or downstream properties. I understand that re- view of these plans is limited to general compliance with the City codes and regulations and does not warrant the engineer’s design or imply and liability to the City of Little Rock for designs contained herein. ____________________________________ William McFadden, P.E. CFM Multi-Hydrograph Plot Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2020 Hyd. No. 1 Pre development Area-1 Hydrograph type = Rational Peak discharge = 7.736 cfs Time to peak = 20 min Hyd. Volume = 9,283 cuft Hyd. No. 3 Post Dev with Pond Hydrograph type = Reservoir Peak discharge = 7.10 cfs Time to peak = 22 min Hyd. Volume = 11,813 cuft 0 5 10 15 20 25 30 35 40 Q (cfs) 0.00 0.00 2.00 2.00 4.00 4.00 6.00 6.00 8.00 8.00 Q (cfs) Time (min) Pre development Area-1 and Post Dev with Pond 2-yr frequency Hyd No. 1 Hyd No. 3 Multi-Hydrograph Plot Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2020 Hyd. No. 1 Pre development Area-1 Hydrograph type = Rational Peak discharge = 8.532 cfs Time to peak = 20 min Hyd. Volume = 10,238 cuft Hyd. No. 3 Post Dev with Pond Hydrograph type = Reservoir Peak discharge = 7.63 cfs Time to peak = 22 min Hyd. Volume = 13,068 cuft 0 5 10 15 20 25 30 35 40 Q (cfs) 0.00 0.00 2.00 2.00 4.00 4.00 6.00 6.00 8.00 8.00 10.00 10.00 Q (cfs) Time (min) Pre development Area-1 and Post Dev with Pond 5-yr frequency Hyd No. 1 Hyd No. 3 Multi-Hydrograph Plot Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2020 Hyd. No. 1 Pre development Area-1 Hydrograph type = Rational Peak discharge = 10.21 cfs Time to peak = 20 min Hyd. Volume = 12,248 cuft Hyd. No. 3 Post Dev with Pond Hydrograph type = Reservoir Peak discharge = 8.50 cfs Time to peak = 23 min Hyd. Volume = 15,342 cuft 0 5 10 15 20 25 30 35 40 Q (cfs) 0.00 0.00 2.00 2.00 4.00 4.00 6.00 6.00 8.00 8.00 10.00 10.00 12.00 12.00 Q (cfs) Time (min) Pre development Area-1 and Post Dev with Pond 10-yr frequency Hyd No. 1 Hyd No. 3 Multi-Hydrograph Plot Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2020 Hyd. No. 1 Pre development Area-1 Hydrograph type = Rational Peak discharge = 11.74 cfs Time to peak = 20 min Hyd. Volume = 14,092 cuft Hyd. No. 3 Post Dev with Pond Hydrograph type = Reservoir Peak discharge = 9.64 cfs Time to peak = 23 min Hyd. Volume = 17,587 cuft 0 5 10 15 20 25 30 35 40 Q (cfs) 0.00 0.00 2.00 2.00 4.00 4.00 6.00 6.00 8.00 8.00 10.00 10.00 12.00 12.00 Q (cfs) Time (min) Pre development Area-1 and Post Dev with Pond 25-yr frequency Hyd No. 1 Hyd No. 3