Combining Hydropower Water Intake and Sediment Bypassing For Improvement of Reservoir Sustainability In A Montane Area: Field Tests

River-borne sediment is a primary issue on the operational application of reservoirs across a river channel. A cascade of loose sediment supplied from hillslope erosion processes usually transforms into river channel networks, leading to serious reservoir sedimentation problems nearby montane regions. Constructed in 1934, the Sun Moon Lake Reservoir (SMLR) in the Western Foothill Belts of Taiwan has been used for hydropower generation, domestic usage, irrigation, especially in recreation. However, this off-stream reservoir has suffered severe sedimentation, incurring the reduction in its storage and lake area in recent years. Till 2019, its accumulated loss of capacity is about 19% and the corresponding sedimentation is about 0.4 Mm3 y-1. To improve sedimentation problems in the SMLR, the field test (47 of totals) of hydropower water intake using sediment-laden flow was investigated to delineate sediment bypass action, addressing the domino effects of sediment bypassing on reservoir area, hydro turbines and its downstream environments. Results show that bypassed sediment concentration reached Chonggui Dam averaging 140 minutes after the beginning of water intake, causing its consequent sedimentation rate of 45.54%. This sedimentation rate could be decreased with hydropower generation time related to subsequent water discharge. Sediment concentration averaged 3.5 hours reaching Shuili Branch, Water Cooperation Company in the downstream, with sedimentation rate of 4.82 %. Moreover, sampling tests indicate no apparent influence of sediment bypassing on the downstream, i.e., the mainstream of Jhuoshuei River. In other words, this study also evaluated sediment abrasion on hydro turbines during the tests and further estimated maintenance costs. These patterns suggest sediment bypass via the process of hydropower water intake is workable and could improve the benefits of sediment removal in the SMLR.