Abstract:Most economic developments may have been at the expense of soil conservation. Soil erosion results in impacts on reservoir sediment, crop yield, and water quality. This study introduces the procedure of using a geographical information system for investigating reservoir sediments and soil erosion of the corresponding watershed. First, the bathymetric surface of a reservoir is surveyed using two real-time kinematic global position systems and a sonar-based depth gauge. Using the on-board computer, receivers, and sonar, bathymetric readings are recorded three times a second to establish actual coordinates and depth measurements. Data are then converted using a digital terrain model to obtain the current image bathymetric surface. The image of original bathymetric surfaces when constructed can be obtained by digitizing the existing map. The subtraction of these two images is used to estimate the amount of sediment deposits. Next, parameters of rainfall-runoff erosivity factor, soil erodibility factor, slope length factor, slope steepness factor, cover-management factor, and support practice factor are evaluated for each grid of the corresponding watershed. The average annual soil loss from each grid is estimated by the revised universal soil loss equation to obtain the total amount of the soil loss for the watershed. Using the example of Charles Mill Lake, Ohio, USA, the estimated average amount of sediment deposits in the lake was about 2Ð44 ð 10 4 m 3 year 1 . On the other hand, the estimated soil erosion from the corresponding watershed was about 4Ð22 ð 10 8 kg year 1 or 1Ð56 ð 10 5 m 3 year 1 . Hence, it can be concluded that about 15Ð6% of the soils eroded from the watershed have been deposited in the lake.

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