An Ounce of Prevention is Worth a Pound of Cure: Erosion Prevention Through Outfall Projects and How They Compare to Traditional Stream Restoration

Brian Roberts, PWS, CPESC
McCormick Taylor
Raleigh, NC

Authors: Scott Lowe and Brian Roberts, McCormick Taylor

Outfall restoration projects have long been passed over in the restoration industry. Various factors, such as current metrics used for determining mitigation requirements and credits, minimal length, higher risk associated with steeper slopes, limiting factors for ecological uplift, etc., have contributed to outfall projects for mitigation credits being disregarded. A search for potential outfall restoration sites throughout the City of Charlotte, North Carolina was conducted using a GIS analysis. This GIS analysis used two approaches using the City of Charlotte’s storm drainage network data, while the second approach used LIDAR data. Potential sites were then field checked and five sites were identified for restoration potential. Traditional stream restoration project sites analyzing nutrient removal rates (by others) using the Chesapeake Bay Protocol 1 (Removal Rates for Individual Stream Restoration Projects) were compared to potential outfall restoration sites in North Carolina using the recently approved Chesapeake Bay Protocol 5, (Removal Rates for Outfall and Gully Stabilization practices). The potential nutrient removal/prevention rates calculated for outfall projects showed 2.5-13 times greater for Total Phosphorus, 5-23 times greater for Total Nitrogen, and 6-30 times greater for Total Suspended Solids per linear foot than traditional stream restoration projects. These outfall sites deliver substantial uplift potential by addressing significant and long term sediment impacts at the source, ultimately improving stream function within the project reach and the downstream watershed. We suggest a linear foot equivalency for outfall projects to determine functional protection or resisting functional degradation as corresponding to functional uplift typically measured for stream mitigation projects.

About Brian Roberts, PWS, CPESC

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