COMBINED HISTORICAL MAPPING, ACOUSTIC SURVEYING, GPS, AND GIS TO INVESTIGATE SEDIMENTATION IN AN URBAN RESERVOIR

Lake Fayetteville (Fayetteville, AR) is a small (176 acres) urban reservoir constructed in 1950. Recently, a civic group expressed concern that land clearing and construction within the watershed had increased sedimentation. To test this claim, an historic engineering map showing pre-impoundment elevations and topographic profiles was compared to echo sounding survey results obtained during summer 2004 using a geographic information system. The pre-impoundment map was scanned and geo-registered within the GIS using a digital orthophoto of the same area as a guide. Once registered, contours on the engineering map were digitized and processed to create a digital terrain model of the pre-impoundment surface. A Knudsen Engineering KEL 320 B/P dual frequency (28/200 kHz) echo sounder was used to acquire present-day bathymetry of Lake Fayetteville for comparison to the pre-impoundment map. Echo sounder data were imported to the GIS to create a digital terrain model of the present-day lake basin. Differential depths reported from of high frequency and low frequency echoes were used to determine sediment thickness exclusively from echo sounder data. In addition, the present-day basin topography (derived from 200 kHz echo data) was compared directly to the pre-impoundment topography within the GIS to determine sediment thickness throughout Lake Fayetteville. Results suggest long-term average sedimentation in Lake Fayetteville was similar to that observed in other lakes throughout northwest Arkansas despite recent land clearing activity within the watershed. Bathymetry and sediment thickness data derived from this comparison provide a baseline for future monitoring of sediment accumulation trends.