Abstract: Session D 11:10 am (Back to Session D)
Reconnection of Old Womans Run to Constructed Forested Wetlands through Strategic Levee Breaches
The Mattawoman Creek Mitigation Site is a mitigation bank site located in Charles County with integrated stream and wetland restoration components. Old Womans Run (OWR), the focus of stream restoration, is a coastal plain stream that was historically straightened to support agricultural production in adjacent fields. During this time, spoils from stream straightening were placed on the banks, creating a levee that effectively reduced the frequency of out-of-bank events and disconnected the stream from its floodplain. In the preconstruction condition, the stream was impaired and was functioning-at-risk. Channel relocation for the restoration of natural coastal plain stream planform was not possible due to site constraints including the potential presence of a state-listed threatened dragonfly species. An alternate approach to achieving full floodplain connectivity was developed that included a total of eight (8) strategically placed levee breaches coupled with the construction of in-stream large woody debris structures. HEC-RAS modeling demonstrated full floodplain connection would be achieved through the proposed design, similar to the complete removal of the levees without the same disturbance. The adjacent floodplain wetland restoration was designed and constructed to retain water for the maximum extent practical during more frequent (1.25, 1.5 year) out-of-bank events supporting infiltration and evapotranspiration. Construction of the project was completed in winter 2018-2019, and effectively reconnected Old Womans Run to 25 acres of restored forested wetland.