Impact Of Reservoir Operation Research Articles

Mixing processes in a reservoir corresponding to different water level operations caused spatial differences during two phytoplankton bloom events

• Two algal bloom events were noticed for the difference in distribution area size. • Water level was the only environmental variable responding to the difference. • Lifting water level induced trapped flow which promoted bloom development. • Continuous conversion from kinetic energy to potential energy are responsible. • The findings provide guidance for reservoir operation design to control algal bloom. Reservoir operation may impact algal blooms by altering flow conditions, but relevant studies and a theoretical understanding of this subject are limited. In this study, two phytoplankton bloom events with different spatial coverage patterns in a reservoir were investigated. By examining environmental variables, a suitable nutrient content and water temperature were considered responsible for bloom initiation during both events, but the different water level operations could possibly explain the observed spatial difference. A two-dimensional hydrodynamic numerical model was then used to simulate the mixing processes within the reservoir during these two bloom events. The simulation results indicated that the rising water level during the bloom event with a larger coverage area caused closed circulation flow conditions above the intrusion layer, displacing surface water in front of the dam upstream until reaching inflowing river water, which then intruded to support water offtake and water level lifting operations, while the other event did not exhibit a similar flow pattern. The water age was sensitive to water level operation, which suggested that phytoplankton dispersal could be promoted by rising water level processes. Inflow densimetric Froude number analysis indicated that reservoir impoundment facilitated a conversion of the inflow kinetic energy into potential energy, thus promoting algal dispersal via circulation. This study provides insights into the impact of reservoir operation on phytoplankton communities, offering a reference for operational design to mitigate algal blooms in reservoirs.

Comparative analysis of routed flood frequency for reservoirs in parallel incorporating bivariate flood frequency and reservoir operation

AbstractFlood frequency is commonly defined by natural flood characteristics such as flood peak, volume and duration. However, for floods at reservoir site, reservoir operation will significantly alter the natural flood process and flood frequency. This article presents a framework of routed flood frequency which incorporates multi‐reservoir flood correlation and considers the effect of reservoir operation. Aggregated flood volume during reservoir operation has been adopted as indicator for the routed flood frequency curve (RFFC). A comparison has been made with a 62‐year series of historic flood inflows observed at two parallel reservoirs in Eastern China. By comparing the derived RFFC with traditional univariate and bivariate flood frequency results, it can be seen that the RFFC results provide a reasonable estimation of flood frequency. A sensitivity analysis indicated that the reservoir maximum release allocation has significant impact on RFFC, and a balanced allocation of flood peak can greatly decrease the overtopping risk. The “peak–peak” contour lines of the RFFC show that there are different flood combination zones which need different operation strategies in real‐time operation. Our findings improve the understanding of flood frequency concepts when considering the impact of reservoir operation and provide reference to manage real‐time reservoir operation.

Impact of reservoir operation on runoff and sediment load at multi-time scales based on entropy theory

Based on the runoff and sediment load data series obtained at the Guide hydrological station (GHS) in the upper reaches of the Yellow River from 1960 to 2013, the varying quasi-periodic fluctuations of runoff and sediment load existing in different decomposed time scales are revealed by using the complementary ensemble empirical mode decomposition (CEEMD) method pre- and post-reservoir operation. Combined with entropy theory, the concepts of multi-time scale entropy (MTSE) and multi-time scale structural entropy (MTSSE) are proposed to analyze the complex fluctuation characteristics of runoff and sediment load at different time scales. The results show that reservoir operation has a greater influence on sediment load than that on runoff at multi-time scales, and that their correlations change as well. Additionally, reservoir operation can aggravate the complexity of the runoff and sediment load, but with longer fluctuation time scales, this complexity decreases and predictability increases. After reservoir operation, the fluctuation period of high frequency components in runoff and sediment load is elongated, and the information content of runoff and sediment load is focused at the short-middle time scale. Therefore, the available and reasonable monitoring and research periods for runoff and sediment load in the upper reaches of the Yellow River are suggested as 4–7 years and 3–4 years, respectively.

A study on the characteristics and influencing factors of reservoir sedimentation in Wanjiazhai Reservoir

Based on measured data of the Wanjiazhai Reservoir in different periods, the characteristics of the spatial and temporal distribution of sedimentation in the reservoir area were preliminarily analyzed and the impact of reservoir operation on this distribution was discussed. Primary conclusions are as followed: in terms of temporal distribution, sedimentation continuously accumulated over the period from 2000 to 2017, with the sediment deposition ratio dramatically decreasing between 2011 and 2017; in terms of spatial distribution, the sedimentation in the reservoir area was mainly concentrated downstream of the WD54 section, with the highest concentration being downstream of the WD23 section. The characteristics of sedimentation distribution in the reservoir area were closely related to inflow and sediment conditions and reservoir operation water level. When the water level was lower than 952 m, the sediment deposition ratio was lower than 0. To further improve the sediment deposition form in the reservoir area, lowering water level and ejecting the sediment are recommended in a timely manner.

Impact of reservoir operation and climate change on the hydrological regime of the Sesan and Srepok Rivers in the Lower Mekong Basin

The transboundary Sesan and Srepok sub-basins (2S) are the “hot-spot” areas for reservoir development in the Lower Mekong region, with 12 reservoirs built in the Vietnam territory. This study examines the impacts of reservoir operations in Vietnam and projected climate change on the downstream hydrologic regime of the 2S Rivers by jointly applying the Soil Water Assessment Tool (SWAT) and Water Evaluation and Planning (WEAP) models. Different scenarios of reservoir operation are considered and simulated to assess their impact on annual, seasonal, and monthly flow regimes under maximum hydropower capacity generation with and without taking into account the minimum flow requirement downstream near the Vietnam border with Cambodia. The precipitation and temperature projections from the high-resolution regional climate model HadGEM3-RA under two Representative Concentration Pathways, 4.5 and 8.5, of HadGEM2-AO are used as future climate change scenarios for the impact assessment. The study results show that reservoir operation leads to an increase in the dry season stream flows and a decrease in the wet season stream flows. The monthly flow regime exhibits considerable changes for both the Sesan and Srepok Rivers but with different magnitudes and patterns of increase and decrease. Climate change is likely to induce considerable changes in stream flows, though these changes are comparatively lower than those caused by reservoir operation. Climate change is likely to have both counterbalancing and reinforcing effects over the impact of reservoir operation, reducing changes during dry season but increasing changes in most of the other months.

AN ASSESSMENT OF THE IMPACT OF RESERVOIR OPERATION ON THE GLOBAL RIVER DISCHARGE

A global river discharge simulation is conducted taking into account the operation of 500 individual reservoirs. The operating rule for each reservoir is estimated by newly developed algorithm and available global datasets since actual operating rule is not published globally. In this algorithm, reservoir operation is categorized into ‘irrigation purpose’ and ‘non-irrigation purpose.’ The latter decreases inter-annual and seasonal fluctuation of discharge, and the former, in addition, supplies irrigation water to meet the demand in downstream. The simulation result is validated with observed data in three reservoirs in three basins, and judged sufficient for global study. Finally, the impact of reservoir operation on river discharge is assessed globally, by comparing RES simulation, global river discharge simulation with reservoir operations, and CTRL simulation, without operations. The result indicates that reservoir operations increase by 4-43% of monthly discharge into oceans in maximum (the world ocean is dividedinto eight oceans), decrease by 1-7%.