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C) ON -SITE DETENTION AND RUNOFF CONTROL PLAN <br />1) The On -Site Detention and Runoff Control Plan shall be reviewed <br />by the administrative authority according to Section 37.07(2) <br />of the Ordinance and the established procedures listed in these <br />guidelines. <br />2) The standards for on -site detention and runoff control shall be <br />as follows: <br />a) Post -development peak runoff rate shall not exceed pre - <br />development peak runoff rate for the same ten (10) year <br />storm event of any duration. <br />b) On -site detention shall safely contain or pass the runoff <br />one -hundred (100) year storm of any duration. <br />3) Acceptable ESTABLISHED PROCEDURES for calculating peak runoff <br />rates and requireddetention SHALL BE AS FOLLOWS: <br />a) Technical Release No. 55 Urban Storm Hydrology For Sma11 <br />Watersheds by U.S.D.A. Soil Conservation Service (including <br />Appendix F). <br />b) Guide For Use Of TR.55 by SCS. September 1981 <br />c) Urban Stormwater Management Special Report No. 49 by <br />American Public Works Association. <br />d) Other up-to-date technical procedures approved by the <br />City Engineer <br />4) Recommended CALCULATIONS ARE AS FOLLOWS: <br />a) . Pre -development Runoff Curve Number of CN = 70 will be the <br />base CN number for undeveloped land in Madison unless <br />soil types or existing condition, excluding vegetative <br />cover, warrant another CN number. <br />b) Peak Discharges <br />1) Worksheet TR Notice 55A September 1981 for Chapter 4 <br />of TR-55 is the worksheet best suited for development <br />of 5 acres or more when less than 60% of the hydraulic <br />drainage length is modified and/or less than 60% <br />imperious surface area is proposed. <br />2) Worksheet TR Notice 55 A September 1981 for Graphical <br />Time Of Concentration (Tc) is best suited for developments <br />listed above which exceed either of the 60% conditions. <br />3) Procedures presented in Chapter 9 of Urban Ltormwater <br />Management APWA Special Report No. 49 are well suited <br />to developments less than 5 acres <br />5) Required DETENTION vOLUMES AND DETENTION ROUTING CALCULATIONS <br />a) Worksheet TR-55 Stormwater Storage Computation should be <br />used, whenever applicable, with methods of Chapter 7 <br />TR-55 to determine storage volumes required for 10 year <br />storms. <br />b) Other methods, as those presented in TR-55 or in APWA Special <br />Report No. 49 and found acceptable by the City Engineer may <br />be used. <br />c) The outflow control structure must provide emergency spillway <br />to safely contain or convey storm flows of a 100 year storm. <br />6) Sample of recommended calculation worksheets are available from City <br />Engineering Division upon request. <br />.3- <br />