Drainage_and_Flooding_Report-dated_10_03_2008

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Mr. Ron Bottoms, City Manager k I o t z a s s o c i a t e s October 1, 2008 Page 9 of 31 arterial streets. Allowing street ponding to depths that keep water within curb lines is not inconsistent with drainage criteria in other communities; that is, allowing limited street ponding is a generally recognized strategy for drainage management in poorly drained areas. P l•ug I tolmi 4 4 J-+2 4 a tie -61 - TAF 1417-IMW4440WIN I • Requiring that the HGL be at or below the street gutter line level. In addition, during extreme flood events (e.g., the 100-year event), in light of the difficulty of drainage in the City because of limited ground slope, we would reconunend reduction in the allowable maximum depth of street ponding, as follows: During a 100-year event storm, the maximum water surface in the street • on the structure is recommended to be the following: • No more than that 3-inches above the top of curb at the highest point of th(i curb adjacent to the lot; 2) no more than 6-inches above the natural ground a!j the highest point of the natural ground along the backside of the curb line; 3) • no • than 3-inches ,.• the roadway crown at the highest ,• within the limits • the lot • • • than that 6-inches ..•.- the top • curb at the lowest •• of the curb • to the lot; 2) no •- than • ,•s the natural ground at the lowest point of the natural ground along the backside of the curb line; 3) and no more than 6-inches ,•• the roadway crown at the lowest •• wiffiin the limits • the lot Data, including applicable calculations and profile plots, should be provided tit the City Engineer demonstrating compliance to these criteria when new development or redevelopment is proposed. NF9,110WITTMIMi 80tWIM1207-711m, 17 Me MinimaT onT ITIT =VV'TF'giVTT1 LW—db'St site mitigation detention storage requirement for drainage areas less than 10 acres, as specified by the current unit storage factors of 0.20 ac-ft/ac and 0.45 ac-ft/ac of detention storage for areas from 0 to 3 acres and from 3 to 10 acres, respectively. In view of the drainage problems currently • faced by the City, these factors rnay be too low to achieve the intended mitigation. Studies previously conducted by Klotz Associates have shown that such unit storage factors in some