Abstract: Session B  9:30 am (BACK)

Stream Restoration Crediting for Meeting Sediment and Nutrient Goals in the Chesapeake Bay

Lisa Fraley-McNeal
Bill Stack
Center for Watershed Protection, Inc.
Ellicott City, MD 

Over the last few decades, the Chesapeake Bay states have pioneered new techniques to restore urban streams using diverse approaches, such as natural channel design, regenerative stormwater conveyance, and removal of legacy sediment. In the future, several states are considering greater use of stream restoration as part of an overall watershed strategy to meet nutrient and sediment load reduction targets for existing urban development under the Chesapeake Bay TMDL. In early 2012, the Chesapeake Bay Program (CBP) convened a panel of experts (the Panel) to review the available science on the practice of urban stream restoration and update the sediment and nutrient removal performance of these practices. The Panel was comprised of practitioners, scientists, and state, local and federal government representatives spanning the entire Chesapeake Bay region. Their goal was to assess whether the existing CBP-approved removal rate was still suitable and to develop practical guidance for quantifying the reductions from stream restoration practices. The Panel’s recommendations are included in the report, Recommendations of the Expert Panel to Define Removal Rates for Individual Stream Restoration Projects, approved on May 13th, 2013.

While there was a paucity of studies that provided actual sediment and reduction rate estimates for specific practices, there were numerous studies that showed typical stream erosion rates were an order of magnitude or greater than existing estimates used for crediting stream restoration practices by the CBP. The Panel opted to throw out the existing CBP-approved rate and used the literature to develop three protocols to estimate sediment and nutrient reduction benefits of stream restoration practices. The first uses estimates of stream erosion rates either through monitoring or modeling methods, such as Rosgen’s BANCS method, and applies a conservative 50% reduction efficiency. The second estimates nitrogen removal during base flow conditions resulting from projects that include instream design features to promote denitrification, and the third estimates the sediment and nutrient reduction that occurs when stream flows are connected to a floodplain wetland. Although the Panel’s recommendations focus on reducing sediment and nutrient loadings, consideration was also given to the importance of stream functions and integration into a comprehensive watershed restoration framework.