Abstract: Session B 8:30 am (Back to Session B)
The Critical and Challenging Nature of Wetland Restoration Water Budget Analysis
Lee W. Forbes, P.E., D.WRE
SWCA Environmental Consultants
Development of the appropriate hydrology is critical to the success of wetland restoration projects within the hydrogeomorphic context. This relates not only to meeting the regulatory thresholds of hydrologic conditions to confirm wetland hydrology, but also to providing the appropriate level of soil wetness and/or ponding within the target duration range to develop a sustainable wetland of the type and Cowardin hydrologic regime desired. It is very rare for actual onsite measurements of site hydrologic conditions over several years to be collected for a proposed wetland restoration site. Instead, these projects typically rely on wetland water budget analyses under existing and proposed conditions and for a variety of dry, normal, and wet year precipitation data to evaluate the project's hydrologic conditions. The basic water budget equation is a mass balance of water in versus water out. The most common form of freshwater wetland restoration projects follow the Pierce method, which relies on relatively impermeable soils to create a perched wetland outside of the channel-forming discharge floodplain, thereby eliminating complex stream overbank flows and groundwater interactions from the water budget equation. However, even this simpler form of the equation is fraught with problematic hydrologic components, such as the prediction of evapotranspiration rates, where the methodologies have been developed almost exclusively for mono-crop agriculture (and not for broadly varied and heterogeneous wetlands) , and the small range of conditions that will yield sufficient hydrology to meet the weltand threshold, yet not so much that extended periods of ponding drastically reduces the types of wetlands and sustainable vegetation that can be achieved. A detailed look at these issues and potential solutions will be presented along with identification of research needs to make these calculations more accurate, universal, and understandable across both the design and regulatory communities.