Drainage_and_Flooding_Report-dated_10_03_2008

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Mr. Ron Bottoms, City Manager October 1, 2008 Page 13 of 31 k I o t z associates Of these types of flood data, Type 1 and Type 2 deal exclusively with structural flooding. The remaining types may deal with structural flooding, street ponding, or other miscellaneous flooding problems. Exhibits 1, 2 and 3 (adapted and updated from Report #1) shows the locations of these flooding reports (segregated by type of flooding incident) across the City. Clustering of the flooding reports is evident. Available data do not provide information sufficient to determine whether various reports of one type are possibly a duplicate of another type (e.g., a report of flooding of a structure by Tropical Storm Allison might duplicate a repetitive loss report of the same structure). To account for such possibility, less weight is given to Type 3 and Type 4 reports of flooding. As a first step to quantitatively describing this clustering and assess its implications for prioritization of projects to remedy long term flooding problems, the location of each report can be spatially evaluated using GIS tools to create a "flooding problem intensity" map (much like a elevation contour map). The to create a parameter representing the number of flooding incidences (as based upon the above four listed types of flooding reports) per unit area (i.e., a flooding intensity). As the number incidences increase in an area, the flooding intensity increases. As this flooding problem intensity increases, the more serious is the flooding problem in an area. That is, this intensity is a measure of flooding problem severity. ese foo ing intensities can Me vista as 077=7 MTirits Since it is only the relative magnitude of the intensities that is important to assessing priorities, the intensities are presented only in relative terms. Review of this flooding intensity map shows there to be "hot spots", i.e. areas of high flooding problem intensity. These are prime areas for remedy of long term flooding problems. It is seen from the exhibits that the hot spots can be easily associated with a particular subdivision or major area within a particular subdivision. Thus it is convenient to identify a hot spot by the subdivision *in which the hot spot is concentrated. As presented in Exhibits 4, 5 and 6, the flooding problem intensities assume that each type of flooding report is of similax importance. However, some types of flooding reports imply a potentially more serious flooding condition than others. For example, a report of repetitive structural flooding is expected to represent a more serious flooding problem than a citizen's single report on a flooding incident associated with Tropical Storm Allison (because of the severity of this storm event) for which the flooding may or may not have been a structural flooding report. Consequently, if more weight is given, from a planning standpoint, to