EVALUATING THE EFFECT OF LAND USE ON PEAK DISCHARGE AND RUNOFF IN THE SARATOGA LAKE WATERSHED

Development in watersheds alters the volume and peak discharge of surface runoff.  Excessive development has implications on groundwater recharge and on the water quality of surface water reservoirs.  In the city of Saratoga Springs, development in the Loughberry Lake watershed (13.7 km²), the current water source, has decreased groundwater recharge and water quality in recent years.  Thus, Saratoga Springs is searching for a new water source and has shown strong interest in tapping the larger Saratoga Lake (watershed of 543 km²).  Municipalities in the Saratoga Lake watershed are planning new developments, particularly increased residential land cover.  Since such development may degrade water quality and alter runoff distribution, we evaluated population and land use from 1980 and 2001 and projected estimates to 2030 to determine how residential development has and will affect surface runoff volumes and peak discharges. 

            We used GIS to create and quantify 1980 and 2001 land use maps of the Saratoga Lake watershed.  We digitized land uses according to the Anderson Land Use codes to represent major land use types.  Land use changes were compared between the 1980 and 2001 maps to find land use change trends.  To determine a viable estimate for future land use change we derived a ratio of population to residential land use size for 1980 and 2000.  We projected the population – residential land use ratio and the estimated population (U.S. Census) to the year 2030 to estimate the residential land use. 

We modeled surface runoff volumes (curve number model) and peak discharges (rational runoff model) based on the land use in 1980, 2001, and 2030.  Development in the watershed increased residential areas 24% between 1980 and 2001, with little increase in commercial and industrial land use.  Population growth yielded an expected residential development increase of 17% by 2030.  Such a change in land use from forest/agriculture land to residential land increased surface runoff volumes by 11% from 1980 to 2001 (5.3 to 5.9 x 10⁶ m³) and would increase runoff volumes by an additional 13% from 2001 to 2030 (5.9 to 6.7 x 10⁶ m³).   Peak discharges increased by 3% from 1980 to 2001 (185 to 191 m³/s) and are estimated to increase by an estimated 5% from 2001 to 2030 (191 to 201 m³/s).