Reservoir Ecological Operation Research Articles

Mitigating adverse impacts of reservoir impoundment on lake ecology: A case study of the Three Gorges Reservoir and Dongting Lake

Upstream reservoir impoundment has brought adverse impacts on the downstream river-connected lakes, including lower water levels, frequent droughts, and reduced biodiversity. Existing research on ecological reservoir operation focused more on the effectiveness of operation redesign for ecology improvement, but less discussion on why they are eco-friendly. In this paper, the reservoir operation mechanisms targeting lake ecology are explored from three perspectives: ecological impoundment strategy, dominant characteristics of ecology and conservation tradeoffs, and critical parameters of the rule curves. Therefore, a reservoir operation framework, which couples the lake hydrological response model and multi-objective optimization model, is developed in this study. This framework is to maximize the water conservation and lake ecology benefits, assessing the latter by ecological reliability and ecological water shortage rate. Taking the Three Gorges Reservoir and Dongting Lake as the case study, operation rule curves are optimized for different impoundment strategies. The results indicate that impoundment with early storage time and slow storage rate can improve the ecological reliability and ecological water shortage by 9.90 % and 16.39 % than conventional operation. The ecological objectives are weakly competitive or synergistic when impounding fast, but strong competitive when impounding slow. Meanwhile, as the storage rate declines, the ecological improvement causes a slight decrease in power generation and a significant decrease in water supply. Finally, the crucial parameters of the rule curves are explored and appropriate values are recommended for different ecological preferences.

An Environmental Operation of Reservoirs through Linking Ecological Storage Model and Evolutionary Optimization

This study proposes an ecological reservoir operation by linking ecological model and optimization model of reservoir. A remote sensing based ecological model was developed in which water temperature and total dissolved solids were simulated in the surface layer of reservoir. Moreover, ecological suitability maps were generated by a fuzzy inference system in which water temperature and total dissolved solids were inputs and normalized suitability was output. An ecological reservoir operation model was developed consistent with the ecological model to minimize ecological suitability loss of the reservoir as well as water supply loss. Moreover, a non-ecological operation was developed to minimize water supply loss only. Reliability and vulnerability indices and average habitat suitability in the reservoir were applied to measure the performance of the optimization model. Results indicated that reliability of water supply is reduced 6% due to using ecological operation model of the reservoir. Furthermore, vulnerability of water supply is increased more than 14% using the ecological operation. In contrast, the average habitat suitability of the reservoir is increased more than 0.35 by ecological operation which means it is remarkably effective on mitigating ecological impacts. Based on case study results, applying ecological operation of the reservoir is necessary to mitigate the ecological impacts of the reservoir on the ecological sustainability of reservoirs as well as downstream. The proposed method is able to balance the habitat requirements and humans’ needs.

Exploring the trade-offs among hydropower benefits, environmental flow, and surface water temperature in a large reservoir under deep uncertainty

The negative environmental impacts of large hydroelectric reservoirs have attracted wide attention. Reservoir operation alters seasonal flow patterns and reduces downstream flow during fish spawning seasons, which may lead to the loss of fish biodiversity. Meanwhile, reservoir impoundment reduces the flow velocity and raises the reservoir surface water temperature (SWT), potentially increasing the risk of algal blooms. While previous studies have designed various operation rules to balance the hydropower benefits and environmental flow or water temperature through multi-objective optimization approaches, a comprehensive analysis of trade-offs among the hydropower benefits, environmental flow, and SWT under an uncertain future remains lacking. This study contributes the many-objective robust decision-making (MORDM) framework to the multi-objective reservoir ecological operation for the first time. We quantify the trade-offs among maximizing the hydropower benefits, maximizing the reliability of environmental flow, and minimizing the number of days with high SWT; and evaluate the robustness of the operation rules under deep uncertainties from the climate conditions and electricity market. We apply MORDM to a large and deep reservoir, Nuozhadu, located in southwest China. Our results indicate that trade-offs exist between environmental flow and SWT, emphasizing the necessity to consider multiple environmental objectives in reservoir operation. Based on MORDM, we identify an operation scheme that can not only balance hydropower benefits and two environmental objectives, but also have robust performance against the uncertain future states. Scenario discovery analysis shows that air temperature is the most important uncertain factor that influences the robustness of operation rules. Our study provides a new perspective on reservoir operation planning to achieve balanced and sustainable developments in hydropower and environments under uncertain climate and electricity market conditions.

Reservoir ecological operation on sediment-laden river considering wetland protection

Reservoir ecological operation has become an important means of ecological protection and restoration. The operation of reservoirs on sediment-laden rivers with water supply, sediment transport, flood control, wetland protection, and power generation as the primary objectives is a challenge in water resources management. Currently, most studies on reservoir ecological operation models involve a single ecological objective, and the inadequacy of the corresponding ecological constraint conditions makes it difficult to optimize reservoir ecological operation. To address these challenges, this study considers comprehensive water shortage, ecological water shortage, effective sediment transport in the river, and reservoir power generation as objective functions to establish an ecological operation model of sediment-laden river reservoirs for wetland protection. In this model, the ecological flow at key sections and water quantity discharged into the ocean are added as the constraint conditions to generate optimal operation schemes that reflect ecological benefits. The case study of the Xiaolangdi Reservoir (XLDR) on the Yellow River, China shows that with this model, the multi-objective requirements of water supply, ecology, sediment transport, flood control, and power generation in the XLDR could be met synergistically by optimizing the average daily discharge of the reservoir. Although the generated ecological operation schemes consider the demand for wetland protection, the reservoir flood control, sediment transport and power generation were not affected, and the latter two even showed improvement. In addition, this model has stronger applicability for large reservoirs. In dry years, small and medium reservoirs require water transfer, water-saving, and other measures required to alleviate water shortage.

A Hybrid Model of Ensemble Empirical Mode Decomposition and Sparrow Search Algorithm-Based Long Short-Term Memory Neural Networks for Monthly Runoff Forecasting

Monthly runoff forecasting plays a vital role in reservoir ecological operation, which can reduce the negative impact of dam construction and operation on the river ecosystem. Numerous studies have been conducted to improve monthly runoff forecast accuracy, of which machine learning methods have been paid much attention due to their unique advantages. In this study, a conjunction model, EEMD-SSA-LSTM for short, which comprises ensemble empirical mode decomposition (EEMD) and sparrow search algorithm (SSA)–based long short-term neural networks (LSTM), has been proposed to improve monthly runoff forecasting. The EEMD-SSA-LSTM model is mainly carried out in three steps. First, the original time series data is decomposed into several sub-sequences. Second, each sub-sequence is simulated by LSTM, of which the hyperparameters are optimized by SSA. Finally, the simulated results for each sub-sequence are summarized as the final results. The data obtained from two reservoirs located in China are used to validate the proposed model performance. Meanwhile, four commonly used statistical evaluation indexes are utilized to evaluate model performance. The results demonstrate that compared to several benchmark models, the proposed model can yield satisfactory forecast results and can be conducive to improving monthly runoff forecast accuracy.

Characteristics and Dfferences of Dissolved Oxygen Stratification in Different Tributaries of Three Gorges Reservoir During Impoundment Period

Taking the Xiaojiang and Xiangxi Rivers, two typical tributaries of the Three Gorges Reservoir, as examples, this study analyzed and compared the hydrodynamic, thermal stratification, and temporal and spatial differences in dissolved oxygen (DO) and their responses to the water storage process in the two tributaries through field monitoring at different stages of the 2020 impoundment period. The results showed that:① at the initial stage of water storage, the DO in the surface layer of the Xiaojiang River was higher (7.00-13.00 mg·L-1) due to atmospheric reoxygenation and phytoplankton photosynthesis, and the oxycline appeared in the water depth of 3-5 m. A large area of anoxia (DO<2.00 mg·L-1) or even an anaerobic sublayer occurred in the water below 5 m. The DO in the Xiangxi River could be divided into three layers vertically:oxygen-rich surface water (8.00-12.00 mg·L-1), middle water (6.00-8.00 mg·L-1), and low-oxygen bottom water (4.00-6.00 mg·L-1). ② Thermal stratification provided a stable physical environment, whereas the upstream inflow and vegetation decomposition in the water-level fluctuation zone increased the content of organic matter, which likely increased the oxygen consumption which was conducive to the formation of an anaerobic bottom layer. In the Xiangxi River, the risk of hypoxia in the bottom water body was low because of the oxygen replenishment from the long-term downslope-bottom density current.③ Continuous monitoring also showed that the storage of the reservoir played a significant role in the replenishment of DO in tributaries, which effectively and rapidly improved the anaerobic phenomenon in the Xiaojiang River. In the Three Gorges Reservoir, it is feasible to ameliorate the water ecological problems such as anoxia and anaerobic conditions in the tributaries via reservoir operation. This study aids understanding of the characteristics and differences of DO stratification in different tributaries of the Three Gorges Reservoir, which can provide theoretical and technical support for reservoir ecological operation.

A Research on the Ecological Operation of Reservoirs Based on the Indicators of Hydrological Alteration

The conventional reservoir operation strategy considering hydropower production ignores the ecology of the downstream rivers and causes a series of environmental problems. To ensure the sustainable development of a reservoir, the operation strategy should consider both the economic benefits of the power station and the ecological benefits in downstream rivers, the key to which is to select suitable parameters for quantifying the ecological objectives of the rivers and incorporate them into the reservoir operation model. To this end, the ecological index (EI) based on the Indicators of Hydrological Alteration (IHA) was developed to reflect the ecology of the downstream rivers, and a reservoir ecological operation model that takes into account the power generation capacity of the power station and the degree of hydrological alteration was constructed, which can be solved using the Non-Dominated Sorting Genetic Algorithm II (NSGA-II). The results show that the mean EI values increase a lot, from 0.24 to 0.62, after the construction of reservoir, and the optimal reservoir operation strategy in each typical year can reduce the hydrological alteration significantly (the reduction rates of both the abundant and dry water years exceed 20%), while ensuring the hydropower production of the power station (the reduction rates of hydropower production are just 1.64%, 3.15%, and 3.16% for abundant, normal, and dry water years, respectively), which provides a good reference for restoring the natural hydrological situation of downstream rivers.

Optimization of ecological reservoir operation rules for a northern river in China: Balancing ecological and socio-economic water use

With the conspicuous contradiction between water use inside and outside rivers, ecological reservoir operation has become a feasible approach to coordinate the relationship between socio-economic water use and ecological water use in rivers. However, ecological water demand in rivers remains difficult to be satisfied in areas facing serious water shortages, resulting in an imbalance between ecological and socio-economic water use. To satisfy the instream ecological water demands in water shortage areas, efforts were made on seeking an optimal reservoir operation scheme to balance the water supply for ecology and socio-economy. This study applied the index of guarantee rate of ecological water (GREW) to ecological river management, improved the previous reservoir operation rules, and constructed an optimization model of ecological reservoir operation rules based on dual-control management indexes. The Dagu River in Qingdao City, China, was selected as a study area to apply this model. The results showed that both the recommended scheme and the scheme without considering ecology could meet the socio-economic water demands, but the satisfaction degree of ecological water demand of the recommended scheme was significantly higher than that of the scheme without considering ecology. The scheme without considering ecology cannot ensure the ecological water demand in the Dagu River, especially for the non-flood season. Comparisons between the recommended scheme and the operation results without considering ecology demonstrated that the optimization model of ecological reservoir operation rules could effectively balance the ecological and socio-economic water use. In conclusion, the optimization model of reservoir operation rules with GREW can solve the problem of competitive water use inside and outside rivers, providing an important scientific basis for water resources management.

Considering ecological flow in multi-objective operation of cascade reservoir systems under climate variability with different hydrological periods

The trade-off between ecological and socioeconomic benefits in the reservoir operation has become a focus issue in the watershed water resource management. However, finding a suitable reservoir ecological operation scheme in the multi-objective cascade reservoir systems remains unclear. At present, most ecological operation models are designed on the basis of water quantity balance, neglecting the dynamic variability of the hydrological process. This study proposed a multi-objective ecological operation system, which coupled a two-dimensional hydrodynamic model with a rainfall–runoff model, and integrated the ecological operation scheme into the hydrodynamic simulation system considering ecological flow. Moreover, the applicability of the operation scheme under climate variability with different hydrological periods was evaluated. Results indicated that multi-reservoir joint operation had the largest effect in normal years; the variation in the monthly hydrological magnitude, extreme events and their duration, temporal change and frequency of streamflow were significantly reduced after reservoir ecological operation. The SAM0-UNICON model performed better than the two other climate models, the ecological deficit (ED) under the Representative Concentration Pathway (RCP) 8.5 climate change scenario was larger than other scenarios with different operation schemes. Future climate change will have a larger impact on discharge change in the wet season than in other hydrological periods. This study emphasises the comprehensive application of the hydrological and hydrodynamic methods, which is of considerable importance for decision-making in basin water resource management and reservoir regulation.

Refined operation of cascade reservoirs considering fish ecological demand

Reservoir ecological operation creates artificial hydrological and hydrodynamic conditions to meet the demand of fish during key life periods, which provides eco-environmental protection to alleviate the negative impact of hydropower development on ecosystems. However, based on practical ecological operation experience, the flow experiments were rough in terms of plan design, most of which were implemented over short time frames, and circumstances where downstream flow conditions existed were inconsistent with fish requirements during periods affected by different local reservoir operation conditions. This finding suggests that current ecological operations leave considerable space for strategy refinement. This study proposed a methodology for designing refined operation strategies incorporating more ecological demands into reservoir operation releases to create and improve suitable ecological conditions for the spawning of representative fish species. A joint water quantity operation model of cascade reservoirs and an under dam-river hydrodynamic model coupling the operation conditions of hydroelectric generators was built. The proposed methodology was applied to the Three Gorges Dam (TGD) and Gezhouba (GZB) Dam cascade reservoirs in China. The simulation results indicated that (1) in most cases, the target of continuous flow increase on an hourly scale could be simply accomplished via hourly joint water quantity operation of TGD-GZB cascade reservoirs. (2) Maintenance of the average Dajiang and Erjiang generator output during the spawning period of Chinese sturgeon at a high outflow of 15000 m3/s could more effectively expand the integrated suitable space of Chinese sturgeon. We aimed to provide suggestions and references suitable for cascade reservoirs in China and worldwide to develop and optimize ecological operation conditions in more refined and diverse ways.

Join tecological operation optimal strategy of control and re-regulation reservoirs: A case study of Three Gorges-Gezhouba cascade reservoirs

全球主要河流已成为受梯级水库控制的人工调节系统.河流鱼类作为淡水生态系统的重要组成部分，在人类对河流水能资源开发利用的进程中，面临着种群退化、多样性丧失的巨大胁迫.水库生态调度是在鱼类关键生命期人为营造满足鱼类需求的水文水动力条件，减缓水库不利生态影响的一种生态环保措施.然而，在生态调度的实践过程中，受水库不同运行方式影响，下游水流条件在局部时段存在与鱼类需求相悖的情况，有进一步提升空间.本文选择了当前世界上规模最大的三峡水电站和其下游的葛洲坝水电站为案例，建立了梯级水库联合调度模型，模拟分析了梯级水库协同运行改善下游河道鱼类繁殖条件的可行性，并探讨了优化调整策略.结果表明，目前三峡、葛洲坝梯级水库生态调度的运行方式，大多数情况下仅通过葛洲坝水库小时尺度的精细调度，就可实现下游四大家鱼产卵繁殖所需的小时尺度连续涨水目标，并可一定程度提升发电出力，达到生态与经济共赢的良好成效.研究结果表明葛洲坝水库有能力在生态调度的特定时期内充分运用反调节库容调节三峡日出库流量过程，可为梯级水库生态调度的优化实践提供积极参考.;The major rivers across the world have become artificial regulation systems controlled by cascade reservoirs. River fish, as an important part of freshwater ecosystems, are under threat of population degradation and biodiversity loss in the process of development and utilization of river water energy resources. The ecological operation of the reservoir is eco-environmental protection to alleviate the negative impact on ecosystems, which artificially creates hydrological and hydrodynamic conditions to meet the requirement of fish during key life periods. However, based on ecological operation practical experience, there are circumstances where downstream flow conditions are inconsistent with the fish requirement in local periods affected by different operation conditions of reservoirs. That means the ecological operation still needs improvement. This paper takes the Three Gorges Dam, the world's largest power station, and the downstream Gezhouba Dam, as a case study, builds a joint operation model of cascade reservoirs, simulates and analyzes the feasibility of the cascade reservoirs to improve the spawning conditions of fish in the downstream river reaches under joint operation and discusses the optimal strategy. In most cases, the target of continuous flow rising for hourly timescale can be accomplished only by the hourly exquisite operation of Gezhouba reservoir, which is required for the four major Chinese carps spawning downstream of Gezhouba Dam. What's more, the hydropower generation output can be improved to a certain extent, thus achieving win-win progress of ecology and economics. The results of this paper show that Gezhouba reservoir can adjust the daily discharge process of the Three Gorges Reservoir by the re-regulation during a specific period of ecological operation, which may function as a useful reference for the optimization practice of ecological operation of cascade reservoirs.

Multi-objective game theory optimization for balancing economic, social and ecological benefits in the Three Gorges Reservoir operation

Reservoir operation is an important and effective measure for realizing optimal allocation of water resources. It can effectively alleviate regional scarcity of water resources, flood disasters and other social problems, and plays an important role in supporting sustainable strategic development of water resources. Coordinating the stakeholders is key to the smooth operation of a multifunctional reservoir. This research examines the competition among stakeholders of a multi-objective ecological reservoir operation aiming to provide for economic, social and ecological demands. A multi-objective game theory model (MOGM) specified 10-day water discharge to meet the triple water demands (power generation, socio-economic consumption and environment) for multi-purpose reservoir operation. The optimal operation of the Three Gorges Reservoir (TGR), with the ecological objective of providing comprehensive ecological flow demanded for some key ecological problems that may occur in the middle and lower reaches of the Yangtze River, was chosen as a case study. Discharged water calculated by the MOGM and a conventional multi-objective evolutionary algorithm/decomposition with a differential evolution operator was then allocated to different demands. The results illustrate the applicability and efficiency of the MOGM in balancing transboundary water conflicts in multi-objective reservoir operation that can provide guidance for the operation of the TGR.

Reservoir ecological operation by quantifying outflow disturbance to aquatic community dynamics

Reservoir operation causes spatiotemporal variations in outflow, which influence the dynamics of downstream aquatic communities. However, empirical evidence of community responses to hydrological alteration remains limited for dam-regulated rivers. This study focused on quantifying the streamflow disturbance to multi-population dynamics in downstream of the China’s Danjiangkou Reservoir. First, the stochastic population dynamics model (PDM) was used to simulate aquatic community dynamics. Then, the flow–ecology relationship was established to identify community response to reservoir outflow. Third, two novel ecological indicators, stable time (ST) and coefficient of variation at stable time (CVST), were proposed to evaluate the resilience and resistance of multi-population systems, respectively. Finally, the reservoir operating rule curves were optimized by considering tradeoffs between socioeconomic and ecological objectives. The coevolution processes of multi-population systems (fish, phytoplankton, zooplankton, zoobenthos, and macrophytes) were simulated by stochastic PDMs. The population densities of stable states showed continuous downward trends with increasing degree of hydrological alteration for multi-population systems, and aquatic community systems could be destroyed when alteration reached its acceptable maximum. The greater the degree of hydrological alteration, the longer the recovery time from an unstable to a stable state, and the weaker resistance for each population system. The resilience and resistance of downstream multi-population systems were enhanced by optimizing reservoir outflow. The optimization results illustrated that the performances of the multiple objectives of water supply, hydropower generation, and ST were improved by 2.37%, 2.40%, and 2.67%, respectively, whereas the performance of CVST was the same as the conventional operation. The flow–ecology relationship provided an approach to quantify the impacts of reservoir outflow on an aquatic community, which is helpful in guiding ecological flow strategies.

Decision Support Model for Ecological Operation of Reservoirs Based on Dynamic Bayesian Network

In this study, a model was proposed based on the sustainable boundary approach, to provide decision support for reservoir ecological operation with the dynamic Bayesian network. The proposed model was developed in four steps: (1) calculating and verifying the sustainable boundaries in combination with the ecological objectives of the study area, (2) generating the learning samples by establishing an optimal operation model and a Monte Carlo simulation model, (3) establishing and training a dynamic Bayesian network by learning the examples and (4) calculating the probability of the economic and ecological targets exceeding the set threshold from time to time with the trained dynamic Bayesian network model. Using the proposed model, the water drawing of the reservoir can be adjusted dynamically according to the probability of the economic and ecological targets exceeding the set threshold during reservoir operation. In this study, the proposed model was applied to the middle reaches of Heihe River, the effect of water supply proportion on the probability of the economic target exceeding the set threshold was analyzed, and the response of the reservoir water storage in each period to the probability of the target exceeding the set threshold was calculated. The results show that the risks can be analyzed with the proposed model. Compared with the existing studies, the proposed model provides guidance for the ecological operation of the reservoir from time to time and technical support for the formulation of reservoir operation chart. Compared with the operation model based on the designed guaranteed rate, the reservoir operation model based on uncertainty reduces the variation range of ecological flow shortage or the overflow rate and the economic loss rate by 5% and 6%, respectively. Thus, it can be seen that the decision support model based on the dynamic Bayesian network can effectively reduce the influence of water inflow and rainfall uncertainties on reservoir operation.

A C-vine copula framework to predict daily water temperature in the Yangtze River

The thermal regime of rivers plays a crucial role in chemical, biological and ecological processes. Effectively predicting water temperature is a key issue related to environment management. This study develops a probabilistic model based on C-vine copulas for water temperature prediction. The proposed framework is applied to forecast daily water temperature in the Yangtze River, considering long-term effects of preceding air temperature and daily discharge. The prediction performance of this framework is compared with the logistic regression model (LogR) and generalized regression neural network (GRNN). The results of this study indicate that the proposed C-vine copula framework and GRNN model provide better forecasting of stream temperature with weak human-related disturbances than LogR model. The outperformance of C-vine framework is reflected by its ability to accurately capture variations in the water temperature greatly affected by the Three Gorges Reservoir (TGR). This steady and reliable framework is further applied for the conservation of Chinese Sturgeon to estimate the range of suggested discharge, given the daily air temperatures, to adjust the water temperature within 18–20 °C at Yichang station during the spawning season. This application is verified to be more effective, providing indications for reservoir management to lower water temperatures by regulating river flow to ensure the occurrence of spawning activities. The results of this study may provide a scientific reference for the ecological operation of reservoirs in regulated rivers.

Reservoir ecological operation considering outflow variations across different time scales

The regulation of reservoirs contributes huge socioeconomic benefits to society at the expense of inducing adverse effects on downstream ecosystems. The reservoir average outflow (such as monthly) can be out of the ecological flow range while the partial daily outflow is suitable due to the outflow fluctuations. To address this issue, the reservoir outflow variations across different time scales (OVDTS) were proposed to form a novel ecological indicator. First, the ecological flow for the full life cycles of indicative native and nonnative species was calculated. Then, the reservoir OVDTS were proposed to describe the streamflow difference between long (e.g., 10-day) and short (e.g., daily) time intervals, and the ecological fitness (namely ecofit) was then formed. Finally, the reservoir operating rule curves were optimized by considering ecofit as well as average annual water supply, water supply reliability, average annual hydropower generation and hydropower generation reliability. The China’s Danjiangkou Reservoir was selected as the case study. It is validated that the established ecofit was almost equal to the proportion of reservoir outflow that met ecological flow range. The ecofit of optimized operating rule curves was improved by 4.19% compared with conventional operation without decreasing the performance of other objectives, also with ecofit improvements of wet, normal, and dry years. It was unexpected that the ecological objective of the optimized operating rule curves was significantly better than that of natural flow mimicry in dry years. The proposed OVDTS and ecofit could be helpful to reservoir ecological operations.

Effects of land use changes on the ecological operation of the Panjiakou-Daheiting Reservoir system, China

The problem of insufficient water for ecological purposes in the Luanhe River basin requires urgent resolution. The regional hydrological cycle is affected by the Panjiakou-Daheiting Reservoir system and by changes in land use in the upper watershed. Therefore, this system was selected as a study area to simulate ecological reservoir operation and analyze the effects of changes in land use on ecological operation. A physical habitat simulation model (PHABSIM) was built to determine the minimum and suitable ecological water demand. Then, an ecological reservoir operation model using an improved differential evolution (DE) algorithm was established. Simulated inflow data under the land use conditions in 1970 and 2015 were input into the model, and the effects of changes in land use on ecological operation and on the weighted usable area (WUA) for cyprinoids were calculated. The results show that ecological reservoir operation significantly improves the ecological water supply and increases cyprinoid habitat. The changes in land use led to a decrease in annual runoff, which further reduced the urban water supply by 0.67%–2.25% and the ecological water supply by 0.45%–2.04% at different flow frequencies. The land use changes also caused the WUA to decrease by 1746–2999 m2/km at different flow frequencies, with a decrease rate of 1.04%–6.28%. This study could provide valuable information for water resource managers operating reservoirs in river ecosystems and planning to cope with water shortages caused by land use change in water-deficient areas.

Study on the Ecological Operation and Watershed Management of Urban Rivers in Northern China

Small- and medium-sized rivers are facing a serious degradation of ecological function in water resource-scarce regions of Northern China. Reservoir ecological operation can restore the damaged river ecological environment. Research on reservoir ecological operation and watershed management of urban rivers is limited in cold regions of middle and high latitudes. In this paper, the urban section of the Yitong River was selected as the research object in Changchun, Northern China. The total ecological water demand and reservoir operation water (79.35 × 106 m3 and 15.52 × 106 m3, respectively) were calculated by the ecological water demand method, and a reservoir operation scheme was established to restore the ecological function of the urban section of the river. To examine the scientific basis and rationality of the operation scheme, the water quality of the river and physical habitat after carrying out the scheme were simulated by the MIKE 11 one-dimensional hydrodynamic-water quality model and the Physical Habitat Simulation Model (PHABSIM). The results indicate that the implementation of the operation scheme can improve the ecological environment of the urban section of the Yitong River. A reform scheme was proposed for the management of the Yitong River Basin based on the problems in the process of carrying out the operation schemes, including clarifying department responsibility, improving laws and regulations, strengthening service management, and enhancing public participation.

Assessment of Hydrological Changes and Their Influence on the Aquatic Ecology over the last 58 Years in Ganjiang Basin, China

Runoff is the key driving factor of the Ganjiang River ecosystem. Human activities such as reservoir construction have greatly changed the state of runoff. In order to analyze the influence of Ganjiang Reservoir on the hydrological regime, the following paper is based on the daily precipitation data of 53 rainfall stations in Ganjiang River Basin from 1959 to 2016, and the daily runoff data of three stations in Dongbei, Ji’an, and Waizhou from 1959 to 2016. The Mann–Kendall test (MK) was used to analyze the trend of precipitation and runoff in Ganjiang River Basin. The Sliding t-Test (ST) was used to determine the abrupt change time of runoff in flood season within typical cross-sections of upper, middle, and lower reaches of Ganjiang River Basin, Ji’an, and Waizhou. Indicators of hydrological change (IHA), range of variability approach (RVA), and other methods were used to analyze the changes of 32 hydrological indicators in Ganjiang River Basin. The results showed that (1) The annual and flood season precipitation in Ganjiang River Basin increased from 1992 to 2016, but it did not reach a significant level. The change of annual runoff at Dongbei and Waizhou Stations was the same as that of the annual precipitation in Ganjiang River Basin. The runoff of Dongbei Station in flood season decreased from 1986 to 2016, and the runoff of Waizhou Railway Station in flood season decreased from 2008 to 2016. It showed that precipitation had a great influence on annual runoff, and human activities made the annual runoff distribution process more uniform; (2) The abrupt changes of runoff in flood season at three hydrological stations in Ganjiang River Basin occurred in 1991, and reached a significant level of 0.01; (3) There were five hydrological indicators of Dongbei Station which had reached height change. The change degree of low (l) pulse duration was −92.24%, the change degree of high (h) pulse count was −86.8%, the change degree of flow rise rate was 87.06%, the change degree of fall rate was −92.24%, and the change degree of number of reversals was −100%. Four hydrological indicators of Ji’an Station had reached high change degree, the count and duration of high pulse changes were −73.33% and −73.65%, the change degree of fall rate was −79%, and the change degree of number of reversals was −100%. Waizhou Station did not reach the high change indicator. The hydrological regime of the upper and middle reaches of Ganjiang River has changed greatly, while the hydrological regime of the lower reaches has changed little. The hydrological regime in the upper and middle reaches of Ganjiang River Basin has been highly changed by human activities such as dam construction. The change of hydrological conditions in the upper and middle reaches of Ganjiang River Basin may reduce the area of aquatic organisms’ habitat, be harmful to the spawning, migration, and survival of aquatic organisms, reduce the interception of organic matter in floodplains, and increase the drought pressure of plants. The reservoir ecological operation of rivers with numerous reservoirs should be considered, joint reservoir dispatching schemes should be formulated for the study area so as to maximize the comprehensive benefits. This study provides a reference for water resources management and reservoir operation in Ganjiang River Basin. The next step is to use a habitat model to simulate the habitat of Ganjiang River Basin.

Multi-objective Decision-Making for the Ecological Operation of Built Reservoirs Based on the Improved Comprehensive Fuzzy Evaluation Method

With the social progress and economic development, people have put forward requirements for the ecological operation of built reservoirs. However, there are conflicts between the ecological landscape and the existing benefits such as irrigation and flood control, so it is necessary to build a decision-making model for the comprehensive value of the ecological operation of reservoirs. Taking a reservoir project which needs to satisfy multi-objective requirements as an example, this paper proposes a set of decision-making methods for ecological operation of built reservoirs based on improved comprehensive fuzzy comprehensive evaluation method and constructs a multi-objective decision-making model and optimization strategy combination. Through case analysis in this paper, the improved comprehensive fuzzy evaluation method has a good effect on multi-objective decision-making of ecological dispatching of built reservoirs. The research shows that the combination strategy of improving the reservoir’s water storage capacity and the water-saving supporting transformation measures has a good effect, which can reduce the waste of the reservoir diversion project and large-scale high-efficiency water-saving transformation project construction. It embodies the idea of water-saving priorities and space balance and has broad application prospects in the optimization of reservoir ecological dispatch.