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Wissahickon Headwaters Restoration and Floodplain Reconnection

Brett Long, PE
Biohabitats, Inc.
Baltimore, MD

Authors: Brett Long & John Ferro

Wissahickon Trails and Biohabitats developed a stream and floodplain restoration plan for a headwater reach of Wissahickon Creek in Upper Gwynedd Township, Montgomery County, Pennsylvania. Collaboration with project landowners, including PECO and Merck Corporation, was critical to this effort.

Stream assessments found the channel to be over-widened and entrenched because of watershed urbanization.  Reconnection of the stream channel to its adjacent floodplain, reducing erosive forces on the stream banks, and restoring riparian habitat were primary project goals.

The restoration design included development of significant floodplain benching and storage as well as moderate raises in channel invert to provide an enhanced connection between the stream and its floodplain.  This channel raise was accomplished by the creation of riffle grade control structures and filling of the existing channel.  No rise in 100-year flood elevations was accomplished by having a net excavation of material in the project channel and floodplain.

The project area has overhead power lines and utility poles throughout, which impacted project design.  Grading in proximity to PECO poles was limited to the maximum extent practicable, while still fulfilling the project goals. Vegetation planting zones are proposed based on location of PECO transmission or distribution lines.  The project was successfully completed in Fall 2020 despite experiencing an extreme precipitation event during construction.  The resilience of the floodplain restoration approach was tested and proven during this extreme event.

About Brett Long, PE

Brett Long, Water Resources Engineer with Biohabitats, has 18 years of experience in environmental engineering design and modeling with a focus on water resources restoration. He has worked with communities throughout the Mid-Atlantic on efforts to design and build green infrastructure and ecological restoration projects. Mr. Long has also has provided project and program management support for MS4 permit holders. Prior to joining Biohabitats, Mr. Long worked as an environmental engineer in Pennsylvania and provided water resources engineering and permitting services for restoration, roadway, park, and redevelopment projects.