Bells Mill

When awarded, this was the largest stream restoration project undertaken in the history of the Philadelphia Water Department

  • Owner: Philadelphia Water Department
  • Location: Philadelphia County, PA

About this Project

AEG completed a comprehensive watershed study of Bells Mill Run and designed stream restoration measures for the Philadelphia Water Department (PWD) and Fairmount Park Commission. Bells Mill Run is a tributary to Wissahickon Creek and part of the Wissahickon Valley, which is listed as a National Natural Landmark by the National Park Service. Along with completing a comprehensive watershed study and analysis, the project involved assessing the watershed’s condition and surveying approximately 5,300 lineal feet of Bells Mill Run’s main branch and tributaries.

AEG assessed watershed conditions, including soils, geology, impacts of stormwater infrastructure, historical and current land uses, cultural resources, vegetation conditions, and threatened and endangered species. These initial assessments enabled AEG to determine processes that may contribute to Bells Mill Run’s degradation. AEG also surveyed locations where infrastructure, including an adjacent sewer line and Bells Mill Road, was being threatened by channel migration of Bells Mill Run. Geographic Information Systems (GIS) were used to collect and map data throughout the watershed, assist with the hydrologic analysis, and compile/process assessment data.

A geomorphic study of the stream was also completed, which enabled the selection of appropriate restoration techniques for Bells Mill’s unique stream type and impairments. The study included a detailed hydrologic and hydraulic analysis. Project hydrology was developed based on the PWD’s Wissahickon Stormwater Management Model (SWMM). AEG calibrated the SWMM model for the unique conditions at Bells Mill Run. Comparative hydrology and local flood history were also collected for the project area to ensure the project’s hydrologic model matched actual conditions. The flows developed by AEG were used to calculate bankfull and flood flows.

AEG prepared project permitting documents, completed threatened and endangered species surveys, and coordinated with the Pennsylvania Historical and Museum Commission to ensure the project had no impact on sensitive cultural or environmental resources.

This stream was severely degraded and contributed large volumes of sediment to the Wissahickon Creek and threatened adjacent Bells Mill Road and the parallel sanitary sewer line. The channel restoration reduced sediment loads to the Wissahickon Creek, helping to meet the Total Maximum Daily Load for Sediment and Nutrients. Channel restoration/stabilization also removed threats to local infrastructure, including roadways, substructure utilities, and maintenance holes.

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