Drainage and Flooding Report January 2009

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k I o t z I i I associates detention for flood water diversion and mitigation of channel capacity improvements, as well as habitat improvement, a community amenity, or, during dry periods, recreational opportunities. Detention ponds can be constructed in phases, with early phases being used to provide detention for diversion or mitigation and later phases being used to provide detention of increased runoff from land development. Table ES-3 lists potential regional detention ponds which could be used to mitigate future land development impacts or, in some cases, also be used for diversion or channel improvement mitigation. Approximate locations of the various detention facilities are shown in Figures ES-1 through ES-6. On -site detention costs are borne by a developer, while regional detention, which combines the necessary detention mitigation for several different development sites into one "regional" detention facility, may be constructed using a variety of funding mechanisms. Costs, all or in part, for regional detention could be borne by developers; the City; by governmental entities partnering with the City; or some combination of these. Estimated costs for construction of the various potential detention facilities, when fully developed, range from $613,000 to $26,752,000. As an aid to assessing these costs, a cost per acre of estimated area available for development upstream of the detention pond is also listed. Cost per acre of developable land ranges from a low of $5,800 to a high of $64,000. Ponds at the higher levels of cost are unlikely to be economically viable; but even for those ponds which are economically viable, the particular ponds which should or will be built will depend to a considerable extent upon how city development patterns evolve over time and the urgency for use of a regional pond. Concluding Remarks This CWDS recommends a variety of drainage improvement and flood control projects, including those that can be relatively easily implemented in the short term, those which are more ES-6 Klotz Associates Project No. 0127.008.000 La Forte Citywide Drainage Study January 2009 City of La Port•-