Abstract: Session A 11:50 am (Back to Session A)
Evaluation of Nutrient Reduction Crediting Strategies for Stream Restoration
Barbara Doll, Ph.D., PE
Extension Assistant Professor
NC Sea Grant & Biological & Agricultural Engineering Dept.
NC State University
Author(s): Jeffrey Johnson, Jonathan Page
As the stream restoration field is currently a $1 billion/yr industry and growing, interest in providing nutrient credits in addition to mitigation credits has been introduced in some states. The Chesapeake Bay Expert Panel first introduced a protocol for awarding nutrient credits for stream restoration efforts. The NC Division of Water Resources (DWR) is currently considering adopting similar voluntary credits that borrow heavily from the current Chesapeake Bay Protocol (CBP). The credit considers three potential nutrient credit elements for stream restoration projects including (1) prevented sediment during storm flow, (2) instream denitrification during base flow and (3) floodplain reconnection.
NC Sea Grant and NC State University conducted a review of the draft standards and tested the proposed nutrient credit calculation methods on four case study restoration projects in order to: 1) quantify the level of effort necessary to prepare nutrient credit estimates, 2) identify opportunities to address shortcomings and simplify the proposed credit standards and 3) where appropriate, develop modified nutrient credit standards for improving application and accuracy of reduction estimates. In addition, USGS gage station data analysis was conducted at five streams to evaluate relationships in channel size, hydrology, watershed size and floodplain flow frequency. In addition, a flood flow frequency analysis was performed to compare observed hydrologic connectivity to floodplains to estimated connectivity as prescribed by the CBP protocol 3. USGS gage data from 5 streams was analyzed and load reductions were computed using water quality data provided by local sources.
Based on the findings of this study, potential revisions to the CBP were recommended including (1) retaining CBP 1 with NC specific streambank concentrations similar to those reported in the 2013 Tetra Tech report and combining CBP 2 and 3 to calculate an areal denitrification partitioned by streambed area and floodplain area; or (2) allowing credit solely based on prevented streambank erosion following CBP 1 with NC specific streambank concentrations. This presentation will outline the results of this study and the proposed credit modifications.