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Broad Creek Park: Valley Wide Floodplain Reconnection and Wetland Creation in an Urban Watershed 

Brad Mowbray
Jessyca Olkowkski
Gannett Fleming
Owings Mills, MD

Authors: Mowbray, Bradley and Olkowski, Jessyca

Urban environments pose a serious challenge to stream restoration practitioners. Impervious area within the watershed of a degraded stream delivers high volumes of concentrated stormwater runoff in a short time span. This water does not arrive to the degraded reach carrying appreciable suspended sediment or bedload. This clear water is very efficient at eroding soft valley bottom soils and creating deeply incised channels whose collapsing walls become a significant source of sediment. In 2018, Gannett Fleming, in Partnership with Arundel Rivers Foundation, designed and implemented a solution for restoring a stream valley with tidal influences near Annapolis Maryland. The goal of the project was to arrest downcutting through valley sediments while reconnecting the floodplain utilizing clay channel plugs, valley wide grade controls, and floodplain roughness features. This project involved work within the Chesapeake Bay Critical Area and hydrologic considerations for tidal and backwater influences needed to be considered. The use of 2D hydraulic modeling in conjunction with digital elevation models (DEM) provided Gannett Fleming with anticipated areas of high shear stress.  This allowed efficient reuse of trees and brush cleared during project construction as floodplain roughness and minimized rock and clay structures that required outside material. The model also was used to determine the that fully filling the existing stream along the valley wall was not necessary to reconnect the floodplain, further optimizing the amount of material needed to be imported for the project.  The low shear stresses encourage deposition of upstream sediments, and we anticipate this system will evolve into a stable anastomosed braided channel. These vertically stable valley wide wetland complexes provide a Win/Win scenario for clients and the environment, allowing for the reestablishment of wetland flora and fauna to a large area while simultaneously generating a generous return of MS4 credit for Protocols 1 through 3.