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Publication Date

2006

Keywords

Reservoir, Sedimentation, Watershed, Sediment yield, Land use, Slope

Abstract

Precision echo sounder surveys of bathymetry and sediment thickness of Lee Creek Reservoir and Lake Shepherd Springs (northwest Arkansas) were combined with Geographic Information Systems (GIS) analyses of watershed digital elevation data and land use/land cover data to evaluate the relative importance of watershed area, watershed physiography, and land use/land cover on sediment yield and reservoir sedimentation. Both reservoirs have comparable surface areas, though Lee Creek Reservoir has approximately one-half the storage capacity of Lake Shepherd Springs (9.47 x 106 m3 versus 18.8 x 106 m3 ) due to the fact that its average depth is approximately 5 m versus an average depth of 9 m for Lake Shepherd Springs. Physiographically, Lee Creek watershed occupies less rugged terrain (94% of slopes <10o) than Lake Shepherd Springs watershed (33% of slopes >10o). Land cover and land use in both watersheds were dominated by forest (83% for Lee Creek Reservoir Watershed; 90% for Lake Shepherd Springs Watershed) and agriculture, though agricultural land use in Lee Creek watershed is nearly twice (15%) that in Lake Shepherd Springs watershed (8%).

Long-term average annual sediment flux to Lee Creek Reservoir was estimated from observed lacustrine sediment volume to be approximately 1.87 x 104 m3 , three times greater than for Lake Shepherd Springs (6.18 x 103 m3 ). However, normalizing long-term average sediment accumulation to watershed area (1,163 km2 for Lee Creek Reservoir versus 173 km2 for Lake Shepherd Springs) showed that the sediment yield (mm m-2 y-1) from Lee Creek watershed (0.16 mm m-2 y-1) was only one-half that from Lake Shepherd Springs watershed (0.35 mm m-2 y-1). This result indicates that slope, rather than land cover and land use, was the dominant control on sediment yield within these two watersheds. Additionally, this study reinforces the importance of considering watershed-scale geomorphic processes in the interpretation of reservoir sedimentation and suggests that simple estimates of reservoir infilling can be misleading indicators of watershed processes.

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