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• methods approved by water quality models designed to <br /> the City. predict the impacts of wetlands on <br /> water quality can be assumed to be <br /> flawed to some degree and subject <br /> to further change. <br /> Selection of an evaluation method <br /> for measuring water quality impacts <br /> resulting from a wetland alteration <br /> is, therefore, difficult. The <br /> existing Ordinance method is based <br /> on the assumption that vegetation <br /> type is key to the effectiveness of <br /> wetlands for stormwater treatment. <br /> This assumption is no longer <br /> considered valid. Retention time <br /> of stormwater is currently <br /> considered the key factor. <br /> Three models based on stormwater <br /> retention have been developed in <br /> recent years. These models are <br /> NURP, WALKER and DETAIN. The NURP <br /> model was developed and calibrated <br /> • for use in stormwater type basins. <br /> The model does not attempt to <br /> quantify the vegetation density and <br /> wetland configuration aspects of <br /> wetland water quality enhancement. <br /> The model has been calibrated to <br /> stormwater ponds. <br /> The WALKER model was developed and <br /> calibrated for reservoirs. This <br /> model similar to the NURP model <br /> does not attempt to quantify <br /> .- . - .nd <br /> configuration aspects of water <br /> quality enhancement. The model was <br /> calibrated to large reservoirs. <br /> The DETAIN model was developed for <br /> use in wetlands and attempts were <br /> made to account for the impacts of <br /> vegetation density and wetland <br /> configuration. The model has not <br /> been calibrated. <br /> • <br /> 2362161/WZO.WP/PLS 18 <br />