CITY IN THE COUNTRY: QUANTIFYING THE EFFECTS OF LAND USE CHANGE ON THE HYDROLOGY OF A WATER SUPPLY WATERSHED, SARATOGA SPRINGS, NEW YORK

Significant recent and projected future growth in Saratoga County, New York, and in the 13.7 km² Loughberry Lake watershed in particular, creates impermeable surfaces, such as roads, parking lots and roofs, that increase runoff volume and peak storm water discharge.  In the Loughberry Lake watershed, most land use change is from well-drained, sandy forests to the mixed impermeable and greenspace land uses of commercial and residential zones.  Such land use change increases the surface runoff and decreases the groundwater recharge that is important to sustain reservoir levels through the high demand summer months.

We quantified land use change from 1980 to 2001, a period of rapid development in the Lake Loughberry watershed.  We used Geographic Information Systems (GIS) to quantify the 1980 data from the Earth Resources Observation Systems (EROS) Data Center (EDC) land use classification that only allows for a generalized estimate of land use areas.  We digitized the 2001, using GIS, from 12” per pixel high-resolution orthophotographic images.  For the 2001 data, we digitized all impermeable surfaces including houses, roads, and parking lots, greenspace, and forested areas.  Thus, the 2001 data are more precise than the 1980 data.

Based on a 10-year 30 minute storm, and using the curve number approach, the total runoff volume has increased 304% from undeveloped conditions of 100% forest cover, similar to the conditions in the 1870s when the reservoir was built.  The runoff volume from 1980 to 2001 for the same design storm has increased 26%.  Using the rational runoff model, peak discharges in 2001 are 160% over the undeveloped condition and 40% higher than the 1980 land use cover.

Such time series measurements of land use change provide useful research experience for undergraduate students and also provides valuable data on the expansion of impermeable surfaces within critical watersheds.  In Saratoga Springs, this project is providing important information on land use practices at a time when the city is concerned about development and its summer water supply.