Document Type

Thesis

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. Flow accumulation data from 27 fields has shown that 51% to 91% of the total area draining to the field margins pass through 10 discrete points, representing <1% of the field margin length. Using in-field observations we have located channels and surface flow evidence within riparian buffers and using GIS we have generated a slope/area relationship at these locations. Our results show a relationship of decreasing slope with increasing area necessary for channel initiation at the buffer. GIS flow accumulation and slope data should be used as precision tools in the placement of riparian buffers to maximize buffer effectiveness and reduce buffer-bypassing.

Date Awarded

2012

Department

Geology

Advisor 1

Gregory S. Hancock

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