Abstract:To explore the influence of the Xiluodu-Xiangjiaba cascade reservoir system on the appropriate environmental flow (AEF) of the Jinsha River, a multiobjective optimal cascade reservoir model was established with the aim of maximizing power generation while minimizing the downstream degree of AEF alteration. The AEF was determined using the range of variability approach (RVA). The optimal model was solved using an improved version of NSGA-II called INSGA2-DS. Inflows in typical normal and dry years were selected… Show more
“…Globally, about two‐thirds of the rivers are disconnected (Grill et al, 2019), and more than 50,000 dams have been constructed and operated in the Yangtze River (Yang et al, 2011) on them. For giant dams built in mountainous areas, the riverbed downstream of the dam has strong scour resistance; hence, the impact of dam operation is limited to changes in hydrological rhythms (Dai et al, 2020). In contrast, for dams built in the transitional zone from a mountain to a plain with sandy riverbed downstream of the dam, the scour resistance of the riverbed is weaker and dam operation has a greater impact on the riverbed's geomorphological system compared to dams built in mountainous areas.…”
This study investigated the influence of the Three Gorges Dam (TGD) on the evolution of nearby channels in the Yangtze River (Changjiang River) system in order to better understand the environmental impact of large‐scale reservoir operations. From 2003 to 2017, the amounts of runoff and sediment transport in the Yangtze River were reduced by 3.3–14.5% and 67.8–92.7%, respectively, relative to 1955–2002 before the TGD was operational. Topographic measurements of the middle reaches (Yichang to Hukou) of the Yangtze River were analyzed from 1975 to 2017, during which time the cumulative erosion of the flood channel was 22.78 × 108 m3, and the dry channel accounted for 90.3% of the erosion. Following commissioning of the TGD, the scouring intensity of the sandy gravel section near the dam initially increased then decreased, whereas the scouring intensity of sandy sections away from the dam continued to increase. Beaches on convex banks of curved sections were scoured, and deep channels on concave banks became silted. In braided sections, the braids tended to shrink, and the diversion ratio of the main branch during dry seasons reduced, resulting in frequent branch alternation. Compared to changes in the downstream river channels of other large reservoirs worldwide, scouring from the TGD is extensive. The findings of this study are significant for river channel regulation and waterway planning in the Yangtze River and worldwide.
“…Globally, about two‐thirds of the rivers are disconnected (Grill et al, 2019), and more than 50,000 dams have been constructed and operated in the Yangtze River (Yang et al, 2011) on them. For giant dams built in mountainous areas, the riverbed downstream of the dam has strong scour resistance; hence, the impact of dam operation is limited to changes in hydrological rhythms (Dai et al, 2020). In contrast, for dams built in the transitional zone from a mountain to a plain with sandy riverbed downstream of the dam, the scour resistance of the riverbed is weaker and dam operation has a greater impact on the riverbed's geomorphological system compared to dams built in mountainous areas.…”
This study investigated the influence of the Three Gorges Dam (TGD) on the evolution of nearby channels in the Yangtze River (Changjiang River) system in order to better understand the environmental impact of large‐scale reservoir operations. From 2003 to 2017, the amounts of runoff and sediment transport in the Yangtze River were reduced by 3.3–14.5% and 67.8–92.7%, respectively, relative to 1955–2002 before the TGD was operational. Topographic measurements of the middle reaches (Yichang to Hukou) of the Yangtze River were analyzed from 1975 to 2017, during which time the cumulative erosion of the flood channel was 22.78 × 108 m3, and the dry channel accounted for 90.3% of the erosion. Following commissioning of the TGD, the scouring intensity of the sandy gravel section near the dam initially increased then decreased, whereas the scouring intensity of sandy sections away from the dam continued to increase. Beaches on convex banks of curved sections were scoured, and deep channels on concave banks became silted. In braided sections, the braids tended to shrink, and the diversion ratio of the main branch during dry seasons reduced, resulting in frequent branch alternation. Compared to changes in the downstream river channels of other large reservoirs worldwide, scouring from the TGD is extensive. The findings of this study are significant for river channel regulation and waterway planning in the Yangtze River and worldwide.
“…The change in the scale of the elite retention in the early stage of the evolution increased the diversity of solutions, while the change in the scale of the elite retention in the late stage enhanced the convergence of the algorithm. 28 Yin et al 29 proposed an improved NSGA-II based on the adaptive variation step size according to the upper and lower boundaries of decision variables to enhance the ability to search the space and achieve a faster solution convergence. Second, to ensure the diversity of the population and avoid reaching the local optimal solution during the optimization search process, the population initialization method or genetic method of NSGA-II can be improved to ensure the distribution of the optimal solution in the entire search space.…”
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“…When a dam is constructed in a mountainous area, the main impact of its operation is on the hydrological rhythms and processes. This could be attributed to the strong anti‐scouring capacity of rivers downstream of the dam (Dai et al, 2020). In contrast, if a dam is constructed in the mountain–plain transitional area and the sandy riverbeds downstream of the dam have weak anti‐scouring capacities, the riverbeds will experience significant scouring that will continue for years.…”
Intensive human activities in river basins have substantial effects on fluvial hydrological and morphological processes and developmental trends. In this study, we assessed the evolutionary characteristics and developmental trends of the fluvial morphological system of the Three Gorges Dam (TGD) downstream to understand the impacts of human activities on the fluvial hydrological–morphological system of the region. The results indicated that the Three Gorges Project (TGP) and other upstream cascade reservoirs promoted sediment retention, which in turn aggravated the trend of declining sediment load and cumulative scouring over a long distance in the channels downstream of the TGD. Approximately 84% of scouring occurred in the low‐water channels, along with thalweg scouring and riverbank collapse. Notably, extended operation of the TGP and other upstream cascade reservoirs has resulted in gradual changes in the downstream riverbeds. Specifically, we found that the most intensive scouring zone shifted downstream from the near‐dam Yichang–Chenglingji reach (0–408 km) to the Chenglingji–Hankou reach. The scouring–silting distribution in swales has also changed: the scouring of deep swales and silting on floodplains prior to the TGP have been replaced by the scouring of both deep swales and floodplains. The scouring intensity of riverbeds in the Yichang–Hukou reach (954 km) was slightly higher than that forecasted prior to the TGP; the scouring intensities increased significantly during 2013–2021, which could be attributed to the TGP and other upstream cascade reservoirs; river sand mining and waterway dredging are secondary factors. We conclude that, owing to the effects of sediment retention by cascade reservoirs in the upper reaches of the Yangtze River (or Changjiang River), the cumulative scouring intensities of riverbeds in the middle and lower reaches of the Yangtze River will continue to increase in future decades.
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