|Piechnik, Denise -|
Submitted to: Extension Fact Sheets
Publication Type: Other
Publication Acceptance Date: February 1, 2011
Publication Date: February 1, 2011
Citation: Piechnik, D., Goslee, S.C. 2011. GIS-based approach improves accuracy of placing pasture best management practices. Extension Fact Sheets. p. 1. Interpretive Summary: An interpretive summary is not requried.
Technical Abstract: Placing Best Management Practices (BMPs) such as buffer strips to intercept flow from a barnyard is a challenge because it can be hard to predict where the water leaving barnyards will enter the stream, or to identify those areas not protected by existing buffers. Water flow direction may change many times before reaching the stream, and these changes may not be obvious, therefore placing a filter strip or buffer in the straight path from the barnyard to the stream may be ineffective. Placing BMPs can be improved by using elevation data with GIS to find the topographic flow paths, the paths that water will actually follow, and to locate areas that are uphill of buffered and unprotected streambanks. We tested this GIS approach on three sub-watersheds of the Spring Creek Watershed (Centre County, Pennsylvania). The Spring Creek Watershed, which ultimately drains into the Chesapeake Bay, has ~30% agricultural landuse within 100m of the stream. High resolution aerial photography clearly shows the presence of barnyards and animal concentration areas such as trees, feeding stations, and waterers. We searched for heavy use areas within 100m of Spring Creek, and found 471. Elevation data for the watershed came from digital elevation models (DEMs) whose grid sizes were 30m, 10m, and 1m. Topographic flow path lengths were much longer than the straight line distances. The median straight path distance was 360m, while the topographic distances were longer: 601m and 690m for the finer-resolution DEMs, and 1080m for the coarsest DEM. Flow length can affect erosion and nutrient transport. Apparent stream entry points varied widely depending on the DEM used. The 1m DEM is the most accurate available, but is hard to work with. The 10m DEM placed flows from concentration areas entering the stream within 10m of where the 1m DEM showed them, but the coarsest DEM put them farther away. The 30m DEM grid cell size was too inaccurate for on-farm planning, but the 10m DEM is good enough to help planners place BMPs. The 10m DEMs are widely available on the internet. This GIS-based tool can help planners place BMPs where they will be most effective at filtering and capturing run-off from animal concentration areas. New concentration areas can be located where runoff will pass through existing buffers instead of flowing straight into the stream.