Linking the effects of land use change with water quality and discharge: an integrated approach

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Virginia Tech


Hydrologic and water-quality equilibria are greatly affected by changing land use. This study presents a methodology that integrates the use of remote sensing, geographical information systems (GIS) and water-quality modeling.

Archived aerial photography proved to be a valuable source of historical land use data. GIS technology was used to compile and analyze spatial data. A comprehensive watershed model was used to link the effects of land use change to water quality.

The Cub Run watershed study area, located in northern Virginia experienced significant land use change between 1979 and 1988. Two aspects of development, impervious surface area and construction activity, that impact discharge and water quality were quantified. Developed land increased 11 percent between 1979 and 1988. Seven percent of the 11 percent increase occurred between 1984 and 1988 with medium-density residential housing and commercial areas accounting for most of the change. As a result of development, the impervious component of the watershed increased 6 percent. Agricultural areas were affected the most by development, decreasing by 13 percent over the 1979 - 1988 time period.

Watershed discharge did not increase as expected with increasing impermeable watershed surface area, indicating that either stormwater control efforts are working and/or the 6 percent increase in impermeable surface area has not affected discharge.

Soil exposed by construction activity increased 5 percent from approximately 1 percent of total surface area in 1979 to 6 percent total surface area in 1988. Significant increases in suspended sediment loads were recorded between 1982 and 1988 when compared to the 1979- 1982 time period. Construction activity is the probable cause of this increase.

A watershed-scale comprehensive water-quality model was successfully calibrated and verified to watershed discharge and, to a lesser degree, suspended solids output. Simulation of suspended solids became less reliable with increased construction activity within the watershed.