Using GIS to Quantify Riparian Buffer Bypassing on Agricultural Fields in the Chesapeake Bay Watershed
Abstract
Forested riparian buffers are intended to reduce the sediment and nutrient loads to streams delivered by agricultural runoff. Within the Chesapeake Bay Watershed, buffers are mandated to be 100' wide along agricultural fields bordered by perennial streams. When flow into buffers is widely disseminated buffers have the potential to significantly reduce pollutant levels entering streams. However, several studies show that flow across buffers is often concentrated, producing channelized flow that bypasses the buffer and presumably reduces buffer effectiveness. Previous studies have relied on field observations in relatively few locations, however, and the extent of bypassing is not well constrained. We hypothesize that buffer bypassing and the associated reduction in buffer effectiveness is a widespread phenomenon. Here we use GIS to determine flow patterns on agricultural fields and to identify locations of concentrated flow through buffers in the Virginia Coastal Plain within the Chesapeake Bay Watershed. Using DEMs with ≤10m resolution, we determine flow accumulation along field margins and identify points with flow accumulation sufficient to generate concentrated flow into buffers. Preliminary data from ~20 fields has been obtained by creating a field outline attached to flow accumulation points generated in ArcMap. We find that 66% to 91% of the total area draining to the field margins pass through discrete points representing <5% of the field margin length. On-field observations show evidence for surface flow and channelization at approximately 90% of the discrete drainage points identified in our hydrologic analysis using GIS. Our preliminary observations suggest buffer bypassing is widespread in this region of relatively low relief. We will present GIS and field analysis from a total of ~50 fields and attempt to identify the area/slope relationship necessary to generate channelization and bypassing at field margins.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2011
- Bibcode:
- 2011AGUFM.H51J1347F
- Keywords:
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- 0483 BIOGEOSCIENCES / Riparian systems;
- 1819 HYDROLOGY / Geographic Information Systems