Upstream Reservoir Operation Research Articles

Fuzzy rule–based control of multireservoir operation system for flood and drought mitigation in the Upper Mun River Basin

Strategic reservoir operation, a primary water management measures, plays a significant role in mitigating floods and droughts. Since the reservoir operation involves making complicated decisions on uncertain hydrological variables driven by climate variability, therefore, constructive tool for decision making like fuzzy logic is essential to optimize reservoir management and ensure water security. This study demonstrated fuzzy logic application to multiple reservoir operation in tropical region like Thailand. A Fuzzy Rule–Based Model (FRBM) exploiting FL approach was developed to control the upstream reservoir operation in the Upper Mun River Basin (UMRB) using the data from 2008 to 2021. Implementing FRBM for UMRB was conducted by identifying two key variables; available water storage and 7–day ahead predicted inflow, as fuzzy inputs. The fuzzy output of the system is the release fraction determined by three operational condition modules; flood, neutral, and drought. For flood module, fuzzy release is primarily determined by the predicted inflow. However, the determination of reservoir release for drought and neutral modules is influenced by the targeted water demand. The results of base case illustrate the capability of FRBM in increasing reservoir storages at the start of dry season by 123.56 MCM/yr in UMRB due to the new daily release schemes generated. This allows supplying water closer to the theoretical agricultural needs and gross irrigation water requirement potentially reducing the risk of water shortfall during consecutive dry years. Whereas, the maximum fuzzy release is constrained corresponding to safe channel capacity of tributaries and Upper Mun river, therefore, downstream flooding is accordingly prevented.

A novel Joint Probability Density Difference Approach for assessing the alteration of hydrologic regime

AbstractThe construction and operation of upstream reservoirs have significantly altered downstream hydrologic regime. Appropriate and quantifiable assessment method for the alteration of hydrologic regime is considerably vital and emergent for ecological protection and restoration. The Range of Variability Approach (RVA) and modified RVA methods have been widely used in practice to assess the hydrological alteration. However, these methods have failed to concurrently describe the distribution of indicator and morphological features in detail, which might inevitably lead to the misjudgment of alteration. This paper proposes a Joint Probability Density Difference Approach (JPDDA) method to address the major drawbacks of these previous methods with the introduction of Gaussian Kernel Density Estimation (KDE) and copula function. The annual average flow is selected as the reference variable to construct a proper joint probability density function between itself and other hydrological alteration indicators. The JPDDA method could describe the marginal distribution in detail through Gaussian KDE and also link the morphological features with copula function. Along with pervious methods, the hydrological alterations at Yichang hydrological station, Yangtze River are estimated based on the measured flow from 1949 to 2022. It is shown that the hydrologic regime has suffered from a moderate or even heavy alteration under the influence of massive upstream cascade reservoirs, and the JPDDA outperforms the other methods in terms of rationality and stability for practical assessments. Thus, the proposed JPDDA method is strongly advised to handle the hydrological alteration and could provide a reasonable reference for ecological operation.

EFFECT OF RESERVOIR UTILIZATION AND OTHER ANTHROPOGENIC ACTIVITIES ON THE HADEJIA RIVER VALLEY FLOODS: A REVIEW

The unceasing risk perception and socio-economic damages caused by flood disasters have been persistent in Hadejia River Valley (HRV). There is, however, a need to review upstream factors that could exacerbate downstream floods in the valley. The review tends to gain insight from the local and global flood occurrences due to the interplay between upstream reservoir management and other anthropogenic activities and downstream floods. The review underscores the impact of poor upstream reservoir operation, agriculture and other anthropogenic activities in exacerbating the occurrence of floods. These activities alter natural drainage patterns, reduce water absorption, and frequent spills from the major dams and hence, amplify runoff resulting in heightened flood risks. It was observed that reservoirs can serve as flood control facilities (if well-managed) and also exacerbate flooding by releasing large volumes of water too quickly or reaching capacity during intense rainfall events. It is, therefore, essential to consider the location, design, and operation of reservoirs, as well as their role within the HRV management context. In conclusion, the Hadejia-Jama’are River Basin Development Authority (HJRBDA) should adopt the Integrated Water Resource Management (IWRM) approach that combines reservoir management, land use, flood forecasting, and emergency response strategies for minimizing downstream flood risks and maximizing the utilization of the upstream reservoirs.

Development of an Optimal Water Allocation Model for Reservoir System Operation

Allocating adequate water supplies under the increasing frequency and severity of droughts is a challenge. This study develops an optimal reservoir system operation method to allocate water supplies from upstream reservoirs to meet the downstream water requirements; validates the proposed optimization model through the system operation of upstream reservoirs; and proposes new water supply policies that incorporate a transformed hydropower reservoir with an add-on water supply function and two multipurpose reservoirs. We use linear programming to develop an optimal water allocation model. This model provides an operational strategy for managing upstream reservoirs with different storage capacities. By integrating the effective storage ratio of each reservoir into the allocation estimation, the model ensures an optimal distribution of downstream water requirements. The results indicated well-balanced, effective storage ratios among the Chungju, Soyanggang, and Hwacheon Reservoirs across varying hydrological conditions. Specifically, during drought years, the average effective storage rates were 20.5%, 20.6%, and 19.07%, respectively. In normal years, these figures, respectively, were 59.3%, 68.6%, and 52.4%, while in wet years, the rates stood at 64.08%, 62.90%, and 54.61%. This study enriches the reservoir operation literature by offering adaptable solutions for collaborative reservoir management and presents efficient strategies for reservoir operations.

Identification and restoration of hydrological processes alteration during the fish spawning period

The hydrological processes play an important role in stimulating fish spawning behavior. Changes in the natural hydrological processes will alter the populations and distribution of fish, which may have a negative impact on the native aquatic organisms. The aim of this study is to identify the alteration of the water rising process during the fish spawning period and to construct an ecological flow optimization model to restore the water rising conditions for fish reproduction. The Mann–Kendall test and the sliding t-test were used to detect the mutation year of the mean daily flow data sets in the fish spawning period in each monitoring year. Then the data sets can be divided into pre-altered and post-altered periods. The water rising process was characterized by the water rising processes count, the duration, the daily flow increase rate, the date of the water rising process, and the initial water rising flow. The changes in hydrological processes in the middle reaches of the Yangtze River were investigated by comparing the post-altered and pre-altered characteristic parameters. Furthermore, we integrated the statistical values of the five characteristic parameters in pre-altered into an ecological flow optimization model to simulate the natural water rising processes for the spawning of the Four Major Chinese Carps (FMCC) and Chinese Sturgeon (CS). The analysis showed that after the hydrological mutation year, the duration and the initial water rising flow in the FMCC spawning season were increased, with hydrological alteration degrees of 63.10% and 70.16%, respectively; however, the daily flow increase rate was significantly decreased, with hydrological alteration of 86.50%. During the CS spawning season, the water rising processes count and the initial water rising flow were dramatically altered parameters, with hydrological alteration degrees of 50.86% and 83.27%, respectively. The former parameter increased, but the latter decreased significantly in the post-altered period. To induce the spawning activity of FMCC and CS, appropriate ecological flows and hydrological parameters were proposed. These results showed that during the spawning seasons of FMCC and CS, the hydrological processes of the middle reaches of the Yangtze River changed significantly. Therefore, ecological flow must be ensured through ecological operation of upstream reservoirs to provide suitable spawning conditions in target fish spawning grounds.

Comparison of Deterministic and Probabilistic Variational Data Assimilation Methods Using Snow and Streamflow Data Coupled in HBV Model for Upper Euphrates Basin

The operation of upstream reservoirs in mountainous regions fed by snowmelt is highly challenging. This is partly due to scarce information given harsh topographic conditions and a lack of monitoring stations. In this sense, snow observations from remote sensing provide additional and relevant information about the current conditions of the basin. This information can be used to improve the model states of a forecast using data assimilation techniques, therefore enhancing the operation of reservoirs. Typical data assimilation techniques can effectively reduce the uncertainty of forecast initialization by merging simulations and observations. However, they do not take into account model, structural, or parametric uncertainty. The uncertainty intrinsic to the model simulations introduces complexity to the forecast and restricts the daily work of operators. The novel Multi-Parametric Variational Data Assimilation (MP-VarDA) uses different parameter sets to create a pool of models that quantify the uncertainty arising from model parametrization. This study focuses on the sensitivity of the parametric reduction techniques of MP-VarDA coupled in the HBV hydrological model to create model pools and the impact of the number of parameter sets on the performance of streamflow and Snow Cover Area (SCA) forecasts. The model pool is created using Monte Carlo simulation, combined with an Aggregated Distance (AD) Method, to create different model pool instances. The tests are conducted in the Karasu Basin, located at the uppermost part of the Euphrates River in Türkiye, where snowmelt is a significant portion of the yearly runoff. The analyses were conducted for different thresholds based on the observation exceedance probabilities. According to the results in comparison with deterministic VarDA, probabilistic MP-VarDA improves the m-CRPS gains of the streamflow forecasts from 57% to 67% and BSS forecast skill gains from 52% to 68% when streamflow and SCA are assimilated. This improvement rapidly increases for the first additional model parameter sets but reaches a maximum benefit after 5 parameter sets in the model pool. The improvement is notable for both methods in SCA forecasts, but the best m-CRPS gain is obtained for VarDA (31%), while the best forecast skill is detected in MP-VarDA (12%).

Quantifying the impacts of hydraulic infrastructure on tropical streamflows

AbstractHydraulic infrastructures, such as reservoirs and water diversion channels, cause altered streamflow worldwide. Therefore, this study aimed to assess the coupled impacts of reservoir operations and water transfer on downstream streamflow over 42 years (1979–2020) for a tropical river in Vietnam, the Vu Gia Thu Bon (VGTB). We also quantified variations in the multi‐sub‐basin contributions to the water budget associated with hydraulic structure development. Therefore, a semi‐distributed hydrological model, SWAT (Soil and Water Assessment Tool), was developed for the entire VGTB basin considering two plausible scenarios: with a dam and without a dam. In this study, reservoirs substantially affected the streamflow during the 2011–2020 period when 12 cascading hydropower dams were constructed in the Vu Gia sub‐basins. The cascading reservoirs across the Vu Gia River reduced the annual average streamflow by 28.1% during this period, whereas their influence was augmented by 13.9% at reaches further downstream. In contrast, the local reservoir and flow diversions created on the Thu Bon River resulted in a 6.5% increase in streamflow. The upstream reservoir operation significantly increased streamflow at the midstream stations by 27.8% compared to the no‐dam period. The streamflow decreased in the dry season by 5.6% in the Vu Gia sub‐basins and increased by 61.7% in the Thu Bon sub‐basins. However, the impacts decreased in the wet season by 41.3% due to the operation of reservoirs, in which Dak Mi 4 had the most significant influence. It was found that the water diverted to the Thu Bon River was governed and reduced by the cascading hydropower dams. Therefore, the operation of 11 reservoirs has partially compensated for the lost water in the Vu Gia sub‐basins, to which the Dak Mi 4 plant has transferred 19.7 m3/s (14%). Our findings classify the impact of cascading dams and diversion structures and their interaction with climate change.

Multidimensional ecosystem assessment of Poyang Lake under anthropogenic influences

Watershed anthropogenic activities, including pollutant discharge, sand mining, and upstream reservoir operation, have increased nutrient loads and decreased water levels and sediment concentrations in Poyang Lake, and thus affected the aqueous ecosystem. In this study, we developed an ecological model from the framework of AQUATOX to simulate the physical, chemical, and biological evolution of Poyang Lake under watershed anthropogenic influences, and used model output for a multidimensional ecosystem assessment of ecosystem structure, function, service, material flow, temporal dynamics, and collapse probability. The potential impacts of a proposed Poyang Lake water conservancy project (PYWCP) to build a sluice near the outlet of Poyang Lake to regulate lake level were explored. Results show that the watershed anthropogenic activities have worsened the Poyang Lake ecosystem. Specifically, the phytoplankton biomass increased, while benthos and fish decreased; the exergy, capacity of nutrient change, and the total biomass-gross primary production ratio decreased; as the lake's volume decreased, fishes’ trophic levels and food web robustness decreased, the food web shrank, single species dependence increased, and ecosystem stability decreased. The PYWCP could mitigate most of these effects, however, it would not recover Poyang Lake to historical conditions, and close monitoring with attention to sluice operational scheduling are required.

Impacts of reservoir operation and urbanization on flood inundation in the Vu Gia Thu Bon Basin, Vietnam

Abstract This study examines the effects of upstream reservoir operation and urbanization on flood inundation in the Vu Gia Thu Bon river basin. The alternative reservoir operation strategies corresponding to the flood storage capacity (Vpl) of 10, 20, and 30% of the active storage capacity (Vhi) are evaluated and compared with the prevailing inter-reservoir operation procedure in terms of inundation effects. The results reveal that increasing the Vpl from 10% to 30% of the Vhi reduces the flooded area by 11.8% and lowers the water level at downstream stations from 6% to 30%. The government's procedure is considered safe to supply water, but the inundation duration is longer, resulting in more damage than the scenario of Vpl=20%Vhi. Regarding urbanization, the expansion of newly urbanized areas has resulted in increased flooding in their surrounding areas, with an increase in flood depth of more than 3 m. Moreover, the new roads have reduced the capacity of flood drainage and caused severe flooding. The water level difference between the two sides of the road can be as high as 2 m. This research will assist managers in developing and implementing appropriate downstream flood control measures.

Statistical and Hydrological Evaluations of Water Dynamics in the Lower Sai Gon-Dong Nai River, Vietnam

The water levels downstream of the Sai Gon and Dong Nai river in Southern Vietnam have been significantly changed over the last three decades, leading to severe impacts on urban flooding and salinity intrusion and threating the socio-economic development of the region and lives of many local people. In this study, the Mann-Kendall (MK) and trend-free prewhitening (TFPW) tests were applied to detect the water level trends and changepoints based on a water level time series at six gauging stations that were located along the main rivers to the sea over 1980–2019. The results indicated that the water level has rapidly increased by about 0.17 to 1.8 cm/year at most gauge stations surrounding Ho Chi Minh City, strongly relating to urbanization and the dike polder system’s impacts that eliminates the water storage space. In addition, the operation of upstream reservoirs has contributed to water level changes with significant consequences since the high-water level at Tri An station on the Dong Nai river occurs 1000–1500 times compared to 300–500 times before the operation. Although the effects of the flows from the sea are less than the two other factors, the local government should seriously consider water level changes, especially in the coastal regions. Our study contributes empirical evidence to evaluate the water level trends in the planning and development of infrastructure, which is necessary to adapt to future changes in Southern Vietnam’s hydrologic system.

Optimisation of reservoir operation mode to improve sediment transport capacity of silt-laden rivers

The inverse relationship between water and sediment is hindering the regulation of sediment in silt-laden rivers. Under natural conditions and insufficient water flow, sediment deposits along river channels, resulting in the accumulation of suspended river sediments above the ground level on both sides of the river. Then, during flooding, dam collapse and overflow can easily occur, threatening the life of residents in floodplain. The operation of upstream reservoirs to maximise the sediment transport capacity of downstream rivers into the sea is deemed the best strategy for the management of silt-laden rivers. However, as incoming water and sediment form a dynamic system, optimising the operation mode of reservoirs has become the most severe challenge in the field. This study proposes a method to remodel the water–sediment relationship of natural rivers by optimising the reservoir operation. First, data were collected and analysed to investigate sediment transport in the downstream river channel and the response relationship between erosion–deposition. Then, an empirical equation for calculating the desired incoming sediment was derived, and the threshold for sedimentary transport balance in the lower reach of silt-laden rivers was determined through mathematical modelling. Finally, the reservoir operation mode was optimised within the threshold range to study the discharge process of the reservoir with the highest sediment transport efficiency downstream. The Yellow River in China exhibits the highest sediment concentration worldwide and was used as a case study to verify the practicability of the proposed method. The critical threshold for sediment transport balance in the lower Yellow River was determined to be 250 million tons. The results demonstrate that the proposed method improved the sediment transport capacity of the lower reaches of the Yellow River. Moreover, it reduced the siltation of the XiaoLangDi Reservoir and the lower reaches of the Yellow River. The XiaoLangDi Reservoir can be jointly operated with the Guxian Reservoir, which is under construction and is expected to maintain the bankfull discharge of the lower reaches of the Yellow River at 4000 m3 for a long time. The optimisation process described in this study can be used to improve the management of silt-laden rivers.

Impacts of climate change and reservoir operation on streamflow and flood characteristics in the Lancang-Mekong River Basin

The Lancang-Mekong River Basin (LMRB) is one of the most important transboundary river basins in Asia. While climate change perturbs the streamflow and affects flood events, reservoir operation may mitigate or aggravate this impact. Therefore, quantitative assessment of the climate change impact and reservoir effect on the LMRB is a vital prerequisite for future hydropower development and environmental protection. This study aimed to estimate the variation of the streamflow and flood characteristics affected by climate change and reservoir operation within the LMRB. A reservoir module was incorporated into the Variable Infiltration Capacity (VIC) model to simulate the streamflow susceptible to the reservoirs. It was found that the reservoirs had a substantial influence on the streamflow during 2008–2016, when many reservoirs were constructed in the LMRB. The reservoirs across the Lancang River (the upper Mekong River located in China) reduced the annual average streamflow by 5% at Chiang Sean station (northern Thailand) in 2008–2016, whereas their influence became undetectable downstream of Vientiane station (northern Laos). The streamflow changes downstream of Mukdahan station at southern Laos (including the stations in Cambodia and southern Vietnam) were mainly attributed to the local reservoirs and climate change. Compared with the baseline period of 1985–2007, the upstream reservoir operation dramatically affected streamflow at the midstream stations with higher dry season streamflow (+15% to +37%), but lower wet season streamflow was less affected (−2% to −24%) in 2008–2016. Climate change increased the magnitude and frequency of the flood by up to 14% and 45%, respectively, whereas the reservoir operation reduced them by 16% and 36%, respectively. Our findings provide insights into the interaction between climate change and reservoir operation and their integrated effects on the streamflow, informing and supporting water management and hydropower development in the LMRB.

Application of remote sensing techniques for analyzing operation of upstream reservoirs in transboundary river basins of Vietnam

Application of remote sensing techniques for analyzing operation of upstream reservoirs in transboundary river basins of Vietnam

Assessing the impacts of reservoirs on downstream flood frequency by coupling the effect of scheduling-related multivariate rainfall with an indicator of reservoir effects

Abstract. Many studies have shown that downstream flood regimes have been significantly altered by upstream reservoir operation. Reservoir effects on the downstream flow regime are normally performed by comparing the pre-dam and post-dam frequencies of certain streamflow indicators, such as floods and droughts. In this study, a rainfall–reservoir composite index (RRCI) is developed to precisely quantify reservoir impacts on downstream flood frequency under a framework of a covariate-based nonstationary flood frequency analysis using the Bayesian inference method. The RRCI is derived from a combination of both a reservoir index (RI) for measuring the effects of reservoir storage capacity and a rainfall index. More precisely, the OR joint (the type of possible joint events based on the OR operator) exceedance probability (OR-JEP) of certain scheduling-related variables selected out of five variables that describe the multiday antecedent rainfall input (MARI) is used to measure the effects of antecedent rainfall on reservoir operation. Then, the RI-dependent or RRCI-dependent distribution parameters and five distributions, the gamma, Weibull, lognormal, Gumbel, and generalized extreme value, are used to analyze the annual maximum daily flow (AMDF) of the Ankang, Huangjiagang, and Huangzhuang gauging stations of the Han River, China. A phenomenon is observed in which although most of the floods that peak downstream of reservoirs have been reduced in magnitude by upstream reservoirs, some relatively large flood events have still occurred, such as at the Huangzhuang station in 1983. The results of nonstationary flood frequency analysis show that, in comparison to the RI, the RRCI that combines both the RI and the OR-JEP resulted in a much better explanation for such phenomena of flood occurrences downstream of reservoirs. A Bayesian inference of the 100-year return level of the AMDF shows that the optimal RRCI-dependent distribution, compared to the RI-dependent one, results in relatively smaller estimated values. However, exceptions exist due to some low OR-JEP values. In addition, it provides a smaller uncertainty range. This study highlights the necessity of including antecedent rainfall effects, in addition to the effects of reservoir storage capacity, on reservoir operation to assess the reservoir effects on downstream flood frequency. This analysis can provide a more comprehensive approach for downstream flood risk management under the impacts of reservoirs.

OMV Petrom starts up PolyFuel unit at Petrobrazi refinery in Romania

Detection and attribution of streamflow changes would be a standing point towards optimizing the management of basin-scale water resources. The Three Gorges Reservoir (TGR), the largest hydropower project worldwide, has recently experienced obvious inflow reduction, which has restricted its capability to achieve the designed electricity generation. This study considered the design period of TGR (1961–1990) as the baseline period for evaluating inflow variations during the subsequent impact period (1991–2015). Annual inflow reduced by 6%, and seasonal inflow significantly decreased by 16% in autumn, which is the main season for filling reservoir. A new stepwise procedure with the help of a water-use model, a lumped hydrological model, and a generic reservoir operation model is presented to unravel the causes of inflow reduction. Results revealed that the drier climate predominantly caused inflow decreases. Human activities have notably enhanced in recent decades, however, they have not posed significant threats to inflow deficiency. Climate variability, water consumption, and upstream reservoir operation contributed by 78%, 15%, and 7% to decrease annual inflow while they contributed by 63%, 4%, and 33% to reduce autumn inflow, respectively. The proposed procedure can quantitatively disentangle major human impacts including water consumption and reservoir regulation. Such information enriches policy makers' knowledge for framing delicacy management of regional human activities in response to changing streamflow pattern.

Attribution of decreasing annual and autumn inflows to the Three Gorges Reservoir, Yangtze River: Climate variability, water consumption or upstream reservoir operation?

Detection and attribution of streamflow changes would be a standing point towards optimizing the management of basin-scale water resources. The Three Gorges Reservoir (TGR), the largest hydropower project worldwide, has recently experienced obvious inflow reduction, which has restricted its capability to achieve the designed electricity generation. This study considered the design period of TGR (1961–1990) as the baseline period for evaluating inflow variations during the subsequent impact period (1991–2015). Annual inflow reduced by 6%, and seasonal inflow significantly decreased by 16% in autumn, which is the main season for filling reservoir. A new stepwise procedure with the help of a water-use model, a lumped hydrological model, and a generic reservoir operation model is presented to unravel the causes of inflow reduction. Results revealed that the drier climate predominantly caused inflow decreases. Human activities have notably enhanced in recent decades, however, they have not posed significant threats to inflow deficiency. Climate variability, water consumption, and upstream reservoir operation contributed by 78%, 15%, and 7% to decrease annual inflow while they contributed by 63%, 4%, and 33% to reduce autumn inflow, respectively. The proposed procedure can quantitatively disentangle major human impacts including water consumption and reservoir regulation. Such information enriches policy makers' knowledge for framing delicacy management of regional human activities in response to changing streamflow pattern.

Impact of the operation of cascade reservoirs in upper Yangtze River on hydrological variability of the mainstream

Abstract. As the impacts by climate changes and human activities are intensified, variability may occur in river's annual runoff as well as flood and low water characteristics. In order to understand the characteristics of variability in hydrological series, diagnosis and identification must be conducted specific to the variability of hydrological series, i.e., whether there was variability and where the variability began to occur. In this paper, the mainstream of Yangtze River was taken as the object of study. A model was established to simulate the impounding and operation of upstream cascade reservoirs so as to obtain the runoff of downstream hydrological control stations after the regulation by upstream reservoirs in different level years. The Range of Variability Approach was utilized to analyze the impact of the operation of upstream reservoirs on the variability of downstream. The results indicated that the overall hydrologic alterations of Yichang hydrological station in 2010 level year, 2015 level year and the forward level year were 68.4, 72.5 and 74.3 % respectively, belonging to high alteration in all three level years. The runoff series of mainstream hydrological stations presented variability in different degrees, where the runoff series of the four hydrological stations including Xiangjiaba, Gaochang and Wulong belonged to high alteration in the three level years; and the runoff series of Beibei hydrological station in 2010 level year belonged to medium alteration, and high alteration in 2015 level year and the forward level year. The study on the impact of the operation of cascade reservoirs in Upper Yangtze River on hydrological variability of the mainstream had important practical significance on the sustainable utilization of water resources, disaster prevention and mitigation, safe and efficient operation and management of water conservancy projects and stable development of the economic society.

Waterbirds in a floodplain: influence of spatial and environmental factors through time

Wetlands are rapidly being lost and fragmented around the world, making it imperative to seek an understanding of the drivers of their diversity. Among aquatic assemblages, birds constitute a conspicuous group that provides many ecosystem services. Here, we use a metacommunity approach to understand the influence of spatial (distance among patches) and environmental factors (local characteristics) in wading bird (Pelecaniformes and Ciconiiformes) assemblages in a river-floodplain system through time. We tested the hypothesis that, due to the small scale of our study, spatial factors have no determinant role in waterbird assemblages, and, due to the annual occurrence of flood pulses, the importance of environmental factors varies through time, according to the hydrological cycle. We tested this hypothesis using Partial Redundancy Analysis (pRDA). We used abundance data for the birds in 20 lagoons, sampled quarterly during two years. The spatial factors did not explain variation in community structure in any sampled month, whereas environmental factors explained variation in the assemblages only in two months. Due to high waterbird mobility, the non-significance of the spatial factor is expected among lagoons in the same floodplain. Environmental factors are important in determining the community structure only in two sampled months, evidencing that their importance varies through time in the floodplain, partially agreeing with our hypothesis. The non-conformity between the influence of environmental factors on assemblages and the hydrological cycle may be due to human impacts caused by the operation of upstream reservoirs, which alter the natural flood events, and caused a long drought period previous to this study. A multiscale approach is fundamental to the understanding on how anthropogenic impacts on wetlands affect waterbird assemblages. Thus, this study contributes to the understanding of how seasonality, environmental conditions of lakes, and a local spatial scale act in structuring waterbird assemblages.

Understanding satellite‐based monthly‐to‐seasonal reservoir outflow estimation as a function of hydrologic controls

AbstractGrowing population and increased demand for water is causing an increase in dam and reservoir construction in developing nations. When rivers cross international boundaries, the downstream stakeholders often have little knowledge of upstream reservoir operation practices. Satellite remote sensing in the form of radar altimetry and multisensor precipitation products can be used as a practical way to provide downstream stakeholders with the fundamentally elusive upstream information on reservoir outflow needed to make important and proactive water management decisions. This study uses a mass balance approach of three hydrologic controls to estimate reservoir outflow from satellite data at monthly and annual time scales: precipitation‐induced inflow, evaporation, and reservoir storage change. Furthermore, this study explores the importance of each of these hydrologic controls to the accuracy of outflow estimation. The hydrologic controls found to be unimportant could potentially be neglected from similar future studies. Two reservoirs were examined in contrasting regions of the world, the Hungry Horse Reservoir in a mountainous region in northwest U.S. and the Kaptai Reservoir in a low‐lying, forested region of Bangladesh. It was found that this mass balance method estimated the annual outflow of both reservoirs with reasonable skill. The estimation of monthly outflow from both reservoirs was however less accurate. The Kaptai basin exhibited a shift in basin behavior resulting in variable accuracy across the 9 year study period. Monthly outflow estimation from Hungry Horse Reservoir was compounded by snow accumulation and melt processes, reflected by relatively low accuracy in summer and fall, when snow processes control runoff. Furthermore, it was found that the important hydrologic controls for reservoir outflow estimation at the monthly time scale differs between the two reservoirs, with precipitation‐induced inflow being the most important control for the Kaptai Reservoir and storage change being the most important for Hungry Horse Reservoir.

Hydrological management for improving nutrient assimilative capacity in plant-dominated wetlands: A modelling approach

Wetland eutrophication is a global environmental problem. Besides reducing pollutant emissions, improving nutrient assimilative capacity in wetlands is also significant for preventing eutrophication. Hydrological management can improve nutrient assimilative capacity in wetlands through physical effects on the dilution capacity of water body and ecological effects on wetland nutrient cycles. The ecological effects are significant while were rarely considered in previous research. This study focused on the ecological effects of hydrological management on two crucial nutrient removal processes, plant uptake and biological denitrification, in plant-dominated wetlands. A dual-objective optimization model for hydrological management was developed to improve wetland nitrogen and phosphorus assimilative capacities, using upstream reservoir release as water regulating measure. The model considered the interactions between ecological processes and hydrological cycles in wetlands, and their joint effects on nutrient assimilative capacity. Baiyangdian Wetland, the largest freshwater wetland in northern China, was chosen as a case study. The results found that the annual total assimilative capacity of nitrogen (phosphorus) was 4754 (493) t under the optimal scheme for upstream reservoir operation. The capacity of nutrient removal during the summer season accounted for over 80% of the annual total removal capacity. It was interesting to find that the relationship between water inflow and nutrient assimilative capacity in a plant-dominated wetland satisfied a dose-response relationship commonly describing the response of an organism to an external stressor in the medical field. It illustrates that a plant-dominated wetland shows similar characteristics to an organism. This study offers a useful tool and some fresh implications for future management of wetland eutrophication prevention.