Precision Conservation Mapping of Buffalo Creek, Union County, PA

Precision Conservation is the application of high resolution geographical data within a Geographic Information System (GIS) to identify key sites to conserve or restore. It can be used to identify locations within a watershed that are likely to contribute unusually large sediment or other pollutant loads into local streams and eventually into the Chesapeake Bay. J. Allenby and C. Phelan from the Chesapeake Conservancy have pioneered a technique to do this. In this project, researchers at Bucknell University worked closely with the Chesapeake Conservancy to apply the technique to Buffalo Creek, a 124 square-mile tributary to the West Branch of the Susquehanna River. Its watershed is mostly forested and agricultural. High resolution (approximately 1 m) remotely-sensed elevation and Land Use / Land Cover (LULC) datasets are used. Using GIS, each cell in the watershed was analyzed to determine the contributing runoff area for the cell. LULC is incorporated by assigning different weights to different land use classes, based on the likelihood that the land use will contribute high pollutant loads. Thus forests have a low weight (2), and crops (7) and parking lots (10) have high weights. A “weighted” contributing area for each cell is found by adding up the weights (rather than just the number) of cells contributing flow to a given cell. The original (un-weighted) and weighted contributing areas are combined into a single metric, the Normalized Difference Flow Index (NDFI). NDFI ranges from -1 to 1. Smaller values correspond to cells with low potential for contributing pollutants and larger values to high potential. NDFI can be visualized on maps by displaying it only for cells having an un-weighted contributing area exceeding a certain value. These cells indicate concentrated flow paths. The value of NDFI along flow paths is indicated (see map) by the color of the flow path, from green (smallest NDFI) to red (largest NDFI). Red flow paths likely carry high pollutant loads. Sites with red flow paths and contributing areas on the order of 10^5 m are targeted for field investigation. At these scales water quality can likely be improved through practices like buffer/filter strips and grass swales