Sedimentation Resurvey Methods: Comparison of Prismoidal Method and Gis Based Method

Sedimentation resurveys determine the distribution of sediment, the depletion or addition of storage in the reservoir, and the trap efficiency of the reservoir. For the 2020 sediment resurvey of Rend Lake, a reservoir in Southern Illinois, two approaches for data collection and volumetric analysis were made. The first approach – Prismoidal Method – uses the 23 historic range lines. The second approach – Digital Terrain Model Comparison (DTMC) – uses a Geographic Information System software, to process approximately 1,100 range lines spaced throughout the lake and subimpoundments. The DTMC Method generally resulted in larger volumes than the Prismoidal Method, with these differences becoming less and less noticeable at increasingly higher elevations. Additionally, numerous coal mine tunnels are known to be located beneath the bottom of the lake. Previous studies hypothesized that abandoned mines were/are causing large areas to subside, resulting in an increased capacity of the reservoir. Using modern survey and data processing methods, this hypothesis is proven to be true. The comparison showed that while the Prismoidal Method produced accurate results with minimal data input, the DTMC Method uses a much larger quantity of data to produce more precise results. Smaller bathymetric details (e.g., the subsidence underneath Rend Lake) cannot be captured by the Prismoidal Method, possibly making it more difficult to look at volumetric changes holistically.