Year Established: 2017 Start Date: 2017-03-01 End Date: 2018-02-28
Total Federal Funds: $25,000 Total Non-Federal Funds: $50,001
Principal Investigators: Ronald Miller, Lucie Guertault
Abstract: More than 2100 upstream flood control reservoirs have been built in Oklahoma to retain floodwaters in upper watersheds. These structures have been constructed with a 50-year life expectancy, and a large number are likely to be approaching or have exceeded their design life. A major concern is related to the continuous filling of reservoirs by sediment detached from the watershed and unstable stream channels and transported during rainstorms that reduces their capacity for flood protection. Only a few site-specific studies have been conducted in Oklahoma to determine reservoir sedimentation rates. Nowadays, numerous rehabilitation projects are carried out by action agencies and conservation districts such as NRCS and Oklahoma Conservation Commission, and the development of accurate tools to assess sedimentation issues in aging reservoirs can provide valuable insights for the planning of these projects. The objective of this project is to quantify the accumulated sediment volume and flood control capacity of various upstream flood control structures located across Oklahoma and identify watershed characteristics (i.e. soil types, soil erodibility and land use practices) which may put storage capacity at most risk due to increased sedimentation. The project aims at developing a model relating mean annual sedimentation rates in reservoirs to watershed characteristics. A substantial part of the project will be dedicated to the collection of the data required to develop the model. Field surveys of a representative sample (about 30-40 reservoirs) of flood control structures across the state will be carried out. The survey will include bathymetry measurements to estimate the storage capacity of the reservoir and sediment core sampling to evaluate the dry bulk density, grain size distribution and spatial variability of sediment deposits. Similar surveys performed recently by other institutions, such as USDA-ARS and USDA-NRCS, will also be utilized in the study. From field surveys, bathymetric maps and area-capacity curves will be developed for the reservoirs. Area capacity curves will be compared to as built data; and used to determine mean annual sedimentation rates. Additionally, GIS and computing software will be used to determine variables quantifying watershed characteristics that will be used for the analysis and modeling. To ascertain explanatory factors of sediment yield to reservoirs, statistical analyses will be performed to evaluate interrelations between reservoir sedimentation rates and watershed characteristics. Next, watershed erosion, dry bulk density and trap efficiency models will be calibrated to reproduce collected data. These models will be evaluated based on their prediction accuracy (provided by evaluation metrics) and the amount of data and calibration required in order to select more suitable models. The extrapolation potential of watershed erosion models will also be evaluated. The potential sources of uncertainty associated with the prediction of reservoir sedimentation will be reviewed and quantified. They include errors related to measurement and processing of the data used to calibrate the model, errors related to the model itself, and errors associated with datasets used for other model inputs such as climate, soils, and land-use. This analysis will help identify the main sources of error and provide potential improvements to reduce prediction uncertainty. The developed model will eventually be used to evaluate the sedimentation in upstream watershed projects and identify sites that might require further investigation for the assessment of rehabilitation needs.