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<br />k lot z 4~. ass 0 cia t e 5 <br /> <br />Since drainage improvements proposed for watercourses are all major drainage ways <br />(bayous, channels, and creeks), the IOO-year design frequency was used to determine <br />needed infrastructure improvements. Currently, the City staff is in the process of <br />updating the storm sewers design frequencies requirements to a 5-year design. While the <br />3-year design is consistent or even slightly more stringent than some other surrounding <br />communities, the City does experience continuing flooding and drainage problems with <br />smaller storm events so a: 5-year level of protection is warranted. <br /> <br />3.1.1.2 Detention Requirements <br /> <br />When storm water detention IS required, the following criteria are used to specify <br />minimum detention: <br /> <br />Greater than 50 acres: <br /> <br />0.20 ac-ft/ac <br />0.45 ac- ft/ac <br />Per HCFCD criteria <br />City and HCFCD approval <br /> <br />o to 3 acres <br />3 to 10 acres <br />IO to 50 acres <br /> <br />Since the detention systems considered for addressing drainage and flooding problems in <br />this CWDS deal with areas typically greater than 50 acres, detention volumes were <br />detennined using hydrologic methods based upon comparison of hydro graph volumes. It <br />should be noted that the City staff is currently in the process of updating the detention <br />requirements for the City. The staff is recommending that a minimum 0.2 ac-ft/ac <br />detention rate be applied to development areas ranging in size from 0 to I acre, while the <br />0.45 ac-ft/ac detention rate is to be used for areas ranging from 1 to 10 acres. These <br />detention rates should provide an additional level of protection to the City. <br /> <br />3-2 <br /> <br />Klotz Associates Project No. 0127.008.000 <br />January 2009 <br /> <br />La Porte Citywide Drainage Study <br />City of La Porte <br />