Boosting spring runoff into the sea by reservoir regulation and its potential for estuarine fishery recovery

With global surge in reservoir construction over the past decades,river systems worldwide have been profoundly fragmented.Consequently,flow manipulation by reservoirs has altered the natural hydrological processes,resulting in extensive modifications of fluvial-marine ecosystems.Mitigating the adverse ecological consequences of reservoirs has become a global concern and has garnered increasing attention.The Yellow River,as one of the most extensively manipulated river systems globally,has experienced substantial changes in the amount and timing of water discharge due to the presence of numerous reservoirs scattered throughout its catchment area.These alterations have caused physicochemical changes in the estuary and subsequent modifications to the estuarine ecosystem.In recent years,the Yellow River Conservancy Committee initiated the release of water through the Xiaolangdi Dam during the major spawning period of fisheries,specifically in the spring,with the aim of improving the estuarine ecological environment.From 2011 to 2020,a total of 84.05 km^(3)of water was discharged from the Xiaolangdi Reservoir during spring seasons,of which 40%(33.16 km^(3))constituted water impounded within the reservoir during preceding months.Correspondingly,the spring water discharge from the Yellow River to the sea increased significantly from 1.50 km^(3)/yr to 3.46 km^(3)/yr in the past decade,leading to a decrease in estuarine salinity by 1.6 PSU.The estuarine fishery resources,such as fish eggs in the Yellow River estuary,have demonstrated evident improvement.The reservoir regulation in the Yellow River,which has successfully enhanced spring water discharge and subsequently restored estuarine fishery resources,presents an effective attempt for mitigating the adverse ecological effects associated with reservoirs.

Reservoir Regulation for Control of an Ancient Landslide Reactivated by Water Level Fluctuations in Heishui River,China

Due to the complex geological processes of Qinghai-Tibet Plateau,numerous deposits,especially the large-scale ancient landslide deposits,are characteristic features of the valleys incised in southwestern China.Intense water level fluctuations since 2011 in Maoergai Reservoir,China,registered the reactivation of Xierguazi ancient landslide,and presented a significant risk to neighboring facilities.Based on detailed field survey and drilling exploration,the landslide was divided into Zone A and Zone B,and other characterizations of landslide were studied as well.To precisely measure the extent of landslide displacement during filling and drawdown stage,surface displacement monitoring system was deployed on the landslide.The monitoring analyses data reveal that reservoir fluctuation is the dominant factor influencing landslide displacement,especially during drawdown stage.Moreover,a future sliding is anticipated in Zone A,while a creep had already existed in Zone B.A reservoir regulation was then established using the lead-lag correlation between reservoir fluctuation and landslide displacement and landslide stability analysis.In the end,the follow-up deformation monitoring demonstrates that the reservoir regulation controlled the landslide effectively.Landslide control by reservoir regulation in Maoergai can serve as a case study for other settlements involved in similar construction activities.

Response of groundwater to the process of reservoirs group regulation and storage in Manas River Basin in Xinjiang

Reservoir regulation and storage is the main approach to alleviate the water pressure caused by the uneven spatial and temporal distribution of surface water resources in arid areas of northwest China.While the regulation and storage of the reservoir affect the conditions of recharge and discharge of groundwater,the process of regional surface-groundwater transformation tends to be complicated.The Manas River basin that lies on the northern slope of Tianshan Mountain in Northwest China was taken in this study as a case.A numerical model of groundwater in basin plain area was established,and the influence of reservoir regulation on groundwater level was studied.The results showed that the total recharge of groundwater in the study area was 75.539 million m3,the total discharge of groundwater was 82.66 million m3,and the groundwater in the study area was in a negative equilibrium state,with a difference of-69.27 million m3.The water balance method was used to verify the comparison.The total recharge of groundwater was 74.34 million m3,the total discharge of groundwater was 80.726 million m3,and the calculation result of the numerical simulation of the supplementary displacement was 63.82 million m3,basically consistent with the calculation result of the water balance method.The reservoir storage method has obvious changes to the groundwater level around the reservoir.The simulation results of groundwater numerical model showed that when the reservoir was in normal operation,the leakage of the reservoir was 27.35 million m3;when the reservoir was operated at low water level,the leakage of the reservoir was the smallest,13.47 million m3.The reservoir has the largest amount of leakage of 41.85 million m3 when operated at water storage level.When the reservoir was operated at the lowest water level,the groundwater level around the reservoir was declining compare to the normal operating water level.The maximum drop of the groundwater observation well was 2.1 m,and the maximum monthly average was 0.99 m.When the reservoir was operating at the normal water storage level,the water level of the groundwater around the reservoir has increased compare to the normal operating water level.The maximum increase of the groundwater observation well was 1.5 m,and the maximum monthly average increase was 0.78 m.The influence of the reservoir on the groundwater level was 2000 m upstream and 12000 m downstream.The research conclusions can provide a scientific reference for the development,utilization and management of regional groundwater.

Flood risk control of dams and dykes in middle reach of Huaihe River

Three stochastic mathematical models for calculation of the reservoir flood regulation process, river course flood release, and flood risk rate under flood control were established based on the theory of stochastic differential equations and features of flood control systems in the middle reach of the Huaihe River from Xixian to the Bengbu floodgate, comprehensively considering uncertain factors of hydrology, hydraulics, and engineering control. They were used to calculate the flood risk rate with flood regulation of five key reservoirs, including the Meishan, Xianghongdian, Nianyushan, Mozitan, and Foziling reservoirs in the middle reach of the Huaihe River under different flood frequencies, the flood risk rate with river course flood release under design and check floods for the trunk of the Huaihe River in conjunction with relevant flood storage areas, and the flood risk rate with operation of the Linhuaigang Project under design and check floods. The calculated results show that （l） the five reservoirs can withstand design floods, but the Xianghongdian and Foziling reservoirs will suffer overtopping accidents under check floods; （2） considering the service of flood storage areas under the design flood conditions of the Huaihe River, the mean flood risk rate with flood regulation of dykes and dams from Xixian to the Bengbu floodgate is about 0.2, and the trunk of the Huaihe River can generally withstand design floods; and （3） under a check flood with the flood return period of 1 000 years, the risk rate of overtopping accidents of the Linhuaigang Project is not larger than 0.15, indicating that it has a high flood regulation capacity. Through regulation and application of the flood control system of the Linhuigang Project, the Huaihe River Basin can withstand large floods, and the safety of the protected area can be ensured.

Assessment of climate change impact on high flows in a watershed characterized by flood regulating reservoirs

A climate-induced extreme flow event such as flooding is one of the most devastating natural hazards,which can significantly damage human lives and properties.This study examined the effects of climate change on the high flow conditions in the Great Miami River Watershed in Ohio under two emission scenarios(RCP 4.5 and RCP 8.5).Streamflow for the 21st century was simulated by utilizing a watershed model-SWAT(Soil and Water Assessment Tool)and 10 different climate outputs from the Coupled Model Intercomparison Project phase 5(CMIP5).The future streamflow was divided into three equal periods:2016-2043(early century),2044-2071(mid-century),and 2072-2099(late century)and independently analyzed to compare high flows of respective intervals with baseline periods(1988-2015).The analysis predicted that 7-day,10-year high-flow(7Q10)would increase by 38%under RCP 4.5 and 44%under RCP 8.5.Similarly,the annual peak flows for study periods were predicted to increase by 26%under RCP 4.5 and 38%under RCP 8.5 from the base period.However,the analysis demonstrated an erratic response for monthly peaks indicating that the peak flow would increase in summer months-May and July to October.Meanwhile,the result did not show any significant increase during the winter season,especially from November to April.The analysis of the four major dams located in the watershed showed that the dam’s peak discharges increase in January,May,and September.Even though increasing peaks were projected in September for the 21st century,the monthly peaks from the watershed outlet were found to be lowest in September as compared to other months.The frequency of future flooding compared to the historical record was found to be increasing in the mid-century under RCP 4.5 and the late century under RCP 8.5.As the future flood is projected to increase,this study finds the reasonable impact of climate change on flood regulating reservoirs/dams in monthly flows.However,daily high flows(90th percentile flow)would be increasing significantly(44%to 250%)under RCP 8.5.