USING BANK ASSESSMENT FOR NON-POINT SOURCE CONSEQUENCES OF SEDIMENT (BANCS) MODEL TO PRIORITIZE POTENTIAL STREAM BANK EROSION on A CATSKILLS MOUNTAIN STREAM

An internship project was initiated with the purpose to assist the Ashokan Watershed Stream Management Program (AWSMP) by evaluating the propensity to model streambank erosion along Birch Creek within Catskill State Park in New York. The project goals that were designed to supplement Birch Creek’s Steam Management Plan include: 1) Establish a baseline dataset to predict an annual stream bank erosion rate of Birch Creek; 2) Rank and Prioritize site specific potential erosion; and 3) produce reach specific erosion ratings. Rosgen’s BANCS (Bank Assessment for Non-point source Consequences of Sediment) model was used as a quantitative tool for estimating erosion. The BANCS model employs both Bank Erosion Hazard Index (BEHI) and Near-Bank Stress (NBS). We obtained an inventory of stream bank conditions on Birch Creek from July 2011 through October 2011. A total of 144 bank locations throughout 6.3 miles of stream were assessed by completing a rapid cross-section, NBS, and BEHI evaluations. Nine monumented stream bank cross-sections were installed and measured pre and post Hurricane Irene and Tropical Storm Lee flood events. BEHI ratings, NBS ratings, and the erosion rates were evaluated. Similar BEHI and NBS ratings produced a range of streambank erosion rates. No apparent trend was observed out of our nine data points but upon further inspection, the discrepancy lied within the NBS ratings. BEHI ratings were plotted against material removed, independently of NBS, which consequently produced a correlated trend line. The monumented cross-sectional data points show that a significant amount of erosion was observed at 5.06 ft²/yr for the highest BEHI rating, the moderate BEHI data points ranged from erosion up to 2.7ft²/yr to minor deposition at .33ft²/yr, and the low BEHI ratings ranged from minor erosion of 1ft²/yr to deposition of 1.7ft²/yr. The discrepancies within the NBS rating may be attributed to the lack of sufficient data points, applicability within the Birch Creek Watershed, or by solely employing a single method from seven possible alternatives to calculate NBS score. A comprehensive management strategy for Birch Creek would suggest that BEHI ratings rather than NBS ratings are an accurate predictor of stream bank erosion for that particular watershed.