Drainage_and_Flooding_Report-dated_10_03_2008

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Mr. Ron Bottoms, City Manager October 1, 2008 Page 12 of 31 k I o t z associates significant cause of the flooding problems. Currently known information on floodplain areas in the City comes from two sources: existing FEMA flood models and survey of channels developed specifically for the CWDS. Only primary channels and bayous are including in these studied channels, so inferences from out -of -bank flooding is restricted to the areas along these studied channels. Exhibit I I shows the location of the studied channels. Section 4 below discusses drainage problems arising primarily from insufficient capacity in major drainage channels. The following section 3.2 examines flooding and drainage problems based not on channel modeling but upon where flooding and drainage problems apparently occur based upon flooding reports, irrespective of the reason for the flooding or drainage problem. The prioritization process presented in this section for resolving flooding and drainage problems recognizes that apparent flooding and drainage problems arise from inadequate storm sewerage capacity, insufficient drainage ditch capacity, capacity limitations at structures, or a combination of these factors. Particular remedies for these inadequate capacities are discussed in Section 5. For the prioritization process discussed utilizes actual flooding data to distinguish both the severity of the flooding problem and the magnitude of the benefit that remedy of the problem will yield, irrespective of the precise cause of the drainage or flooding problem. 1JW 11 a 0 1 0 1 If The City has collected and Klotz Associates has assembled for evaluation the following types of flooding reports: • Report Type 1: Reports on severely damage residences • Report Type 2: Repetitive loss reports on structural (residential) flooding • Report Type 3: Tropical Storm Allison flooding in 2001. (It is noted that in the area of the Texas Medical Center at peak rainfall conditions, 8.5 inches of rain fell within one 2-hour period. This would exceed a I 00-year storm event; see Appendix B) • Report Type 4: Tropical Storm Erin flooding in 2007. (It is noted that this storm event had a frequency of a 100 to 500 year event, depending upon location, for the maximum 3-hour period of rainfall during the storm event.) may become available which provides flooding data. Thus, to deal with such potential, there is also introduced: