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Readily Available Hydrologic Models: Pertinence to Regulatory Application

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Technical Report

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Engineer Research and Development Center (U.S.) Vicksburg United States

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Water is the driving force of wetlands. Hydroperiod represents both the frequency and duration of inundation or soil saturation whether it is from flooding or ponding. The formation of hydric soils and an expression of hydrophytic vegetation are evidence of the hydroperiod, which can be described along a gradient of hydrologic conditions Figure 1. Hydrologic modeling provides a means to establish wetland hydroperiod, including current wetland hydrologic conditions and forecasting future conditions in response to future with and without wetland impacts or restoration actions. Today, fast computer processing and hydrologic models allow the user to make a large number of computations very rapidly on potentially large volumes of data. Currently, there is a myriad of hydrologic models available that offer an array of applications. For regulatory application, accurate determination of wetland hydrology is paramount to the following - Confirm wetland hydrologic criteria in accordance to the US Army Corps of Engineers Wetland Delineation Manual 1987 Manual and Regional Supplements. - Establish frequency and duration hydroperiod of wetland ponding and flooding. - Conduct wetland functional assessments including identification of predominant water sources. - Estimate wetland impacts from regulated activities. - Determine ecological lift in response to restoration actions compensatory mitigation. - Establish performance standards and success criteria for compensatory mitigation. - Facilitate development of a monitoring and adaptive management plan. The objective of this report is to provide a treatise of hydrologic models that offer specific application to establish wetland hydrology for existing and future conditions in response to regulated activities and restoration actions. The emphasis is on the suitability of existing hydrologic models to hydrogeomorphic HGM wetland classes. HGM subclasses are not addressed in this technical note.

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