Maximizing the habitat restoration potential of controlled releases at hydropower dams; Understanding impacts of hydrograph form on sediment transport
- University of Idaho
Regulation of streamflow for hydropower often alters natural hydrographs, commonly reducing peak flows, increasing baseflows, and increasing ramping rates. Simultaneously, reservoirs typically trap sediment, reducing the supply to the reach downstream of the dam. These changes to the flow regime and sediment supply impact channel morphology and sediment transport processes in ways that reduce the diversity and suitability of instream habitat. A variety of restoration approaches have attempted to mitigate for some of these changes and a growing number include releases of high flows designed to mimic key characteristics of the pre-regulation hydrograph. One example is the Trinity River, CA, where the addition of augmentation gravel to the channel has been combined with high flows designed to restore portions of the pre-regulation hydrograph to improve channel conditions for spawning fish on the Trinity River, CA. Another example is the high-flow experiments on the Colorado River through the Grand Canyon that aim to restore eroding sand bars that not only provide habitat but camping for rafting groups. More projects that restore portions of the pre-regulation hydrograph are likely in the future because the Federal Energy Regulatory Commission (FERC) requires habitat mitigation efforts in the relicensing process for hydropower facilities. However, the outcomes of these costly restoration efforts are often hard to predict because little is known about how hydrograph form actually impacts channel morphology and bedload transport in rivers. Here we summarize the results of two flume experiments designed to investigate the impacts of hydrograph form on the morphology of a channel bar and bedload transport processes. The first experiment primarily investigated the impacts of hydrograph recession rate on the morphology of a channel-bar in a sand bed channel. Additional runs examined the combined effects of hydrograph recession and a dense patch of vegetation on bar form. The second flume experiment investigated bedload transport processes in an armored, gravel bed channel during hydrographs with varying form. It documented total bedload flux for a hydrograph, bedload flux rates, persistence of the coarse armor surface, and changes in bed surface structure. Both experiments observed links between hydrograph form and the resulting bar morphology or bedload transport processes, providing insight into ways that high flow hydrographs can be designed to better facilitate restoration goals downstream of hydropower facilities.
- Research Organization:
- Hydropower Foundation
- Sponsoring Organization:
- USDOE Office of Energy Efficiency and Renewable Energy (EERE), Renewable Power Office. Water Power Technologies Office
- DOE Contract Number:
- EE0006506
- OSTI ID:
- 1638637
- Country of Publication:
- United States
- Language:
- English
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