Upstream Reservoir Research Articles

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.

Spatial-temporal Variation in Water Quality and Its Response to Precipitation and Land Use in Baiyangdian Lake in the Early Stage of the Construction of Xiong'an New Area

To assess the water quality of Baiyangdian Lake in the early stage of construction of the Xiong'an New Area, the water quality data in Baiyangdian Lake from December 2020 to November 2021 were collected from five typical monitoring stations. Using the remote-sensing interpretation of land use types, Pearson correlation analysis, comprehensive pollution index, and principal component analysis, the spatial-temporal variation characteristics of the water quality and its response to precipitation and land use structure at different spatial scales were explored in Baiyangdian Lake. The results showed that:① the water quality of Baiyangdian Lake was the best in spring and the worst in summer. Nutrient pollution was the heaviest at Nanliuzhuang, which was greatly affected by the Fuhe River. Organic pollution was the heaviest at Caiputai. ② The comprehensive pollution index of Nanliuzhuang was the highest, followed by that of Shaochedian, Guangdianzhangzhuang, Caiputai, and Quantou. The main excessive pollutant was TN, and the pollution index of 1.55 reached the level of severe pollution. The water quality of Baiyangdian Lake was significantly better than that before the construction of the Xiong'an New Area. ③ The construction land and cropland within the 1.5 km buffer zone had the greatest impact on turbidity, NH4+-N, and TP. While the reed wetland acted as the "sink" for intercepting and absorbing pollutants, it also released nitrogen into the 800 m buffer zone, which was the "source" of the pollutants. ④ The correlation between water quality indicators and land use structure in the rainy season was lower than that in the dry season. This was due to the dilution effect of the upstream reservoir discharging in the rainy season, which weakened the impact of pollutants in the rainfall runoff on the water quality of Baiyangdian Lake.

Res-CN (Reservoir dataset in China): hydrometeorological time series and landscape attributes across 3254 Chinese reservoirs

Abstract. Dams and reservoirs are human-made infrastructures that have attracted increasing attention because of their societal and environmental significance. Towards better management and conservation of reservoirs, a dataset of reservoir-catchment characteristics is needed, considering that the amount of water and material flowing into and out of reservoirs depends on their locations on the river network and the properties of the upstream catchment. To date, no dataset exists for reservoir-catchment characteristics. The aim of this study is to develop the first database featuring reservoir-catchment characteristics for 3254 reservoirs with storage capacity totaling 682 595 km3 (73.2 % of reservoir water storage capacity in China) to support the management and conservation of reservoirs in the context of catchment level. To ensure a more representative and accurate mapping of local variables of large reservoirs, reservoir catchments are delineated into full catchments (their full upstream contributing areas) and intermediate catchments (subtracting the area contributed by upstream reservoirs from the full upstream part of the current reservoir). Using both full catchments and intermediate catchments, characteristics of reservoir catchments were extracted, with a total of 512 attributes in six categories (i.e., reservoir and catchment body characteristics, topography, climate, soil and geology, land cover and use, and anthropogenic activity characteristics). Besides these static attributes, time series of 15 meteorological variables of catchments were extracted to support hydrological simulations for a better understanding of drivers of reservoir environment change. Moreover, we provide a comprehensive and extensive reservoir dataset on water level (data available for 20 % of 3254 reservoirs), water surface area (99 %), storage anomaly (92 %), and evaporation (98 %) from multisource satellites such as radar and laser altimeters and images from Landsat and Sentinel satellites. These products significantly enhance spatial and temporal coverage in comparison to existing similar products (e.g., 67 % increase in spatial resolution of water level and 225 % increase in storage anomaly) and contribute to our understanding of reservoir properties and functions within the Earth system by incorporated national or global hydrological modeling. In situ data of 138 reservoirs are employed in this study as a valuable reference for evaluation, thus enhancing our confidence in the data quality and enhancing our understanding of the accuracy of current satellite datasets. Along with its extensive attributes, the Reservoir dataset in China (Res-CN) can support a broad range of applications such as water resources, hydrologic/hydrodynamic modeling, and energy planning. Res-CN is on Zenodo through https://doi.org/10.5281/zenodo.7664489 (Shen et al., 2022c).

STUDYING THE FLOOD REGULATION CAPACITY OF THE RED RIVER UPSTREAM RESERVOIR TO OVERCOME INCIDENTS AT LIEN MAC DYKE

This article presents a study on the flood regulation capacity of the upstream reservoirs of the Red River. One and two-dimensional numerical analyses have been carried out to simulate the hydraulic flow of the upstream reservoir and the downstream river network. The effectiveness of flood mitigation in a number of reservoi capacity scenarios have been estimated. Calculation results show that, the capacity of reservoirs of 5,553 million m3 would likely reduce the the flooded downstream area by 47,528 ha in case using a part of the capacity of the construction. The time when the reservoirs completely close the floodgates without discharging water to the downstream is from 27 to 30 hours, which is adequate for the Lien Mac dyke to be completely rectified within 24 hours.

Reservoir Reliability as Affected by Climate Change and Strategies for Adaptation

Reservoir operational reliability indicates how satisfactorily the structure meets the water demand without failure. However, due to the stochastic nature of its operation, every combination of reservoir storage capacity and draft has an associated probability of failure (i.e., of having an empty reservoir). The objectives of this research were to design a method to assess reservoir reliability under present and future climate conditions, and to apply it to the Descoberto reservoir, with a capacity of 86 hm3 and a design draft of 182.9 hm3 yr−1, located in central Brazil. The scenarios were the historic (1986–2005) and future RCM projection ensembles (2031–2050 and 2061–2080, RCP 4.5 and 8.5). Projected runoff was obtained with the Gardner model, and the reservoir budget was assessed by the concatenated behavior analysis (CBA). The reliability of the Descoberto reservoir, which was 100% during the historic period, was reduced to 15–50%, depending on the future climate scenario analyzed. The proposed adaptive measures, involving the reduction of reservoir draft and the increase in reservoir storage, were capable of maintaining a 100% reservoir reliability under the new climatic conditions, but with associated costs. The proposed method can be applied to other upstream reservoirs, providing water managers and stakeholders with a simple and robust reliability assessment and climate adaptation tool.

Decoupling of nitrogen, phosphorus and biogenic silica in floodplain sediments in response to land use change and hydrological alterations

Human activities are altering global biogeochemical cycles of nitrogen (N), phosphorus (P) and biogenic silica (BSi). In order to reveal nutrient dynamics in response to human disturbances, this study explores burial rates and ratios of N, P and BSi in 210Pb-dated sediment cores from eight lakes in the middle Yangtze River floodplain. Mean burial rates of N, P and BSi increased substantially from the early 20th century, except for a hiatus in the 1970s. Before the 1960s, the stable ratios of N:P, N:BSi and P:BSi indicated the nutrient supply from clastic sources, while arable land expansion enhanced nutrient burial in lakes. Although damming increased the retention of N, P and BSi in upstream reservoirs after the 1960s, anthropogenic N and P release to the lakes outpaced the retention by dams, as suggested by continuous increases in N and P burial rates. The concurrent increase in BSi burial rate suggested that nutrient enrichment promoted diatom production at the earlier stage, while rising N:BSi and P:BSi ratios and declining BSi burial rate from the 1990s indicated the Si depletion with further eutrophication. Spatial heterogeneities among the lakes were linked to site-specific factors such as hydrological connectivity and macrophyte growth. Synchronous increases in N, P and BSi burial rates before the 1960s mainly responded to deforestation and arable land expansion; thereafter, the decoupling of N, P and BSi likely resulted from intensive farming (e.g., fertilizer usage) and damming. Given new dam construction and land use change in river basins, the BSi depletion relative to N and P is likely occurring in riverine floodplains worldwide.

A Control Program for Hydropower Operation Based on Minimizing the Principal Stress Values on the Dam Body: Mosul Dam Case Study

This study examines the vibrations produced by hydropower operations to improve embankment dam safety. This study consists of two parts: In the first part, ANSYS-CFX was used to generate a three-dimensional (3-D) finite volume (FV) model to simulate a vertical Francis turbine unit in the Mosul hydropower plant. The pressure pattern result of the turbine model was transformed into the dam body to show how the turbine unit's operation affects the dam's stability. The upstream reservoir conditions, various flow rates, and fully open inlet gates were considered. In the second part of this study, a 3-D FE Mosul dam model was simulated using an ANSYS program. The operational turbine model's water pressure pattern is conveyed to the dam's turbine-shared zone. The maximal and minimal upstream reservoir water levels were investigated. A control program was created depending on the principle stress model results collected from the operation of the hydropower plant with the minimum principal stress on the dam body. This research suggests an enhanced turbine operating system, reducing stress on the dam body and increasing dam operation life.

Application of 210Pbex in elucidating contemporary sedimentary dynamics in the water-level fluctuation zone of the Three Gorges Reservoir, China

Excess 210Pb (210Pbex) has been widely applied as a proxy indicator for establishing the chronology of sediments in lakes where the sedimentation processes comply with the assumptions for using 210Pbex dating models. However, little is known regarding the applicability of 210Pbex to elucidate contemporary seasonal sedimentary dynamics in reservoir water-level fluctuation zones (WLFZs). In the present study, sedimentary core and bulk sediments were collected from the WLFZ of the Three Gorges Reservoir (TGR) in China, and the physical and chemical properties were determined. Results for 210Pbex activity, total organic carbon, and total nitrogen of bulk sediments indicate pronounced elevation-dependent spatial variation (p < 0.05), but 137Cs activity and particle composition show no systematic trends, allowing 210Pbex activity to be used to differentiate seasonal stratigraphy. For the sedimentary core, therefore, sediment layers with lower 210Pbex activity were inferred to represent sedimentation during wet seasons, when the 210Pbex concentration was diluted by a higher suspended sediment load, whereas sediment layers characterised by higher 210Pbex activity were ascribed to sedimentation during dry seasons, when the tranquil water favoured 210Pbex fallout to be absorbed by suspended sediments and then deposited in the WLFZ. Hereupon, temporal variation is observed in annual sedimentary thickness, with relatively low sedimentation rates during the initial stage (2006–2008) of the TGR impoundment, followed by relatively high sedimentation rates from 2009 to 2013. Over the period from 2014 to 2017, sedimentation rates were low because the suspended sediment was intercepted by upstream cascade reservoirs. Subsequently, sedimentation rates were higher during 2018–2019 as a consequence of an increase in extreme rainfall events. The findings herein highlight that 210Pbex-based seasonal stratification discrimination is effective approach to establish high-resolution sedimentary chronosequences and that net sedimentation rates in WLFZ are controlled by inflow suspended load of the TGR.

Reshuffling of the sediment suspension regime in the “starving” middle Yangtze River downstream from cascade mega-reservoirs

The impoundment of cascade mega-reservoirs in the upper Yangtze River (uYR) has exerted profound and accumulative impacts on the lower reaches—not only a drastic drop in the incoming sediment load but also overturning of the runoff-sediment relationship. Based on a 1990–2021 dataset, we examined fundamental changes in the sediment suspension regime in the Jingjiang reach, approximately 100 km below the Three Gorges Dam (TGD). The cascade mega-reservoir impacts are elucidated by three parameters: inflow water discharge and sediment concentration released to the Three Gorges Reservoir (TGR) and operating water levels in front of the TGD. The wash-load concentrations in the reach in the post-TGR period illustrate strong relationships with the flow capacity index, they, however, were actually determined by the above three parameters. The relative importance of the three parameters in determining the wash-load concentrations was evaluated by a random forest model. After upstream reservoir impoundment starting in 2003, the unsaturation degrees in the reach tended to increase, and the thresholds distinguishing wash-load and bed-material-load have risen to ∼0.125 mm and ∼0.25 mm at SS/JL and ZC after TGD impoundment, respectively. In addition, the flow capacity coefficients, i.e., m and k, in the “starving” reach became significantly lower than their equilibrium counterparts. The study aims to facilitate effective management of the uYR cascade mega-reservoirs and the experience could be drawn on for other large rivers facing hydropower development.

Multi‐stakeholder approach to implementing water stewardship: The case of the Ghod River basin

AbstractITC Limited, an Indian conglomerate company under the Water Stewardship Programme, works to achieve water security for all the stakeholders in its manufacturing unit and agriculture value chain catchments. Under the programme, ITC has developed a methodology for implementation: (1) assessment and creation of an annual water balance in basins and aquifers; (2) develop a plan for making water balance positive throughout the year for today and tomorrow; (3) collaborative action by engaging with the community and other stakeholders for achieving a positive water status. Accordingly, ITC works with government in public private partnership (PPP) mode to merge resources and expertise for enhanced outreach. The Ghod River is a tributary of the Krishna River which flows in Maharashtra, a prominent agricultural state in India. The upper ridges of the basin receive 3000 mm while lower areas receive 450–500 mm rainfall annually. The basin has a total storage potential of 1280 MCM (million cubic metres) in reservoirs in the upper ridges. The Ghod River basin has a positive water balance on an annual basis, but in the post‐monsoon season it has a deficit of 61.9 MCM. To manage the water deficit in the post‐monsoon season, there is a need to: (i) restore upstream reservoirs to their original storage capacity by reducing silt load; (ii) increase subsurface flows into reservoirs throughout the year through managed aquifer recharge; (iii) reduce demand for water primarily from agriculture. ITC has initiated work on those lines based on scientifically rigorous and socially inclusive approaches.

National‐Scale Detection of Reservoir Impacts Through Hydrological Signatures

AbstractReservoirs play a vital role in the supply and management of water resources and their operation can significantly alter downstream flow. Despite this, reservoirs are frequently excluded or poorly represented in large‐scale hydrological models, which can be partly attributed to a lack of open‐access data describing reservoir operations, inflow and storage. To help inform the development of reservoir operation schemes, we collate a suite of hydrological signatures designed to detect the impacts of reservoirs on the flow regime at large‐scales from downstream flow records only. By removing the need for pre‐and‐post‐reservoir flow timeseries (a requirement of many pre‐existing techniques), these signatures facilitate the assessment of flow alteration across a much wider range of catchments. To demonstrate their application, we calculate the signatures across Great Britain in 111 benchmark (i.e., near‐natural) catchments and 186 reservoir catchments (where at least one upstream reservoir is present). We find that abstractions from water resource reservoirs induce deficits in the water balance, and that pre‐defined flow releases (e.g., the compensation flow) reduce variability in the downstream flow duration curve and in intra‐annual low flows. By comparing signatures in benchmark and reservoir catchments, we define thresholds above which the influence of reservoirs can be distinguished from natural variability and identify 40 catchments significantly impacted by the presence of reservoirs. The signatures also provide insights into local reservoir operations, which can inform the development of tailored reservoir operation schemes, and identify locations where current modeling practices (which lack reservoir representation) will be insufficient.

The drainage of glacier and ice sheet surface lakes

Supraglacial lakes play a central role in storing melt water, enhancing surface melt and ultimately in driving ice flow and ice shelf melt through injecting water into the subglacial environment and through facilitating fracturing. Here, we develop a model for the drainage of supraglacial lakes through the dissipation-driven incision of a surface channel. The model consists of the St Venant equations for flow in the channel, fed by an upstream lake reservoir, coupled with an equation for the evolution of channel elevation due to advection, uplift and downward melting. After reduction to a ‘stream power’-type hyperbolic model, we show that lake drainage occurs above a critical rate of water supply to the lake due to the backward migration of a shock that incises the lake seal. The critical water supply rate depends on advection velocity and uplift (or more precisely, drawdown downstream of the lake) as well as model parameters such as channel wall roughness and the parameters defining the relationship between channel cross-section and wetted perimeter. Once lake drainage does occur, it can either continue until the lake is empty, or terminate early, leading to oscillatory cycles of lake filling and draining, with the latter favoured by large lake volumes and relatively small water supply rates.

Evaluation of sediment management strategies for Tarbela reservoir

Globally, multipurpose large dams play significant roles by providing water for irrigation, flood control and hydropower. This study aims to evaluate different strategies for the evacuation of deposited sediments in Tarbela reservoir by using Hydrologic Engineering Center-River Analysis System. Sediment flushing from existing power tunnels was found infeasible due to the downstream constraints and the loss of hydropower. New sediment bypass tunnels on the right-side bank of the dam to overcome the constraints were analysed. The sediment balance ratio, long-term capacity ratio and economic analysis were computed along with sediment modelling for different scenarios. The most technically viable scenario was 90 days flushing at 390 m drawdown level with a discharge of 5000 m3/s. This scenario was not economically feasible in terms of net present value, internal rate of return and the benefit cost ratio. The upstream under construction Diamer Basha dam was also evaluated. The results suggested a large volume of sediment would be trapped in the upstream reservoir, which would ultimately lead to a significant reduction in the inflow of sediment and the delta movement in the Tarbela reservoir. This option was recommended due to its multiple benefits and potential capacity to enhance Tarbela reservoir's life.

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%).

Research on Seawater Intrusion Suppression Scheme of Minjiang River Estuary

Seawater intrusion in the Minjiang River estuary has gravely endangered the water security of the surrounding area in recent years. Previous studies mainly focused on exploring the mechanism of intrusion, but failed to provide a scheme for suppressing seawater intrusion. The three most relevant determinants to chlorine level, which represented the strength of seawater intrusion, were determined using Pearson correlation analysis as being the daily average discharge, daily maximum tidal range, and daily minimum tidal level. Considering the lower requirement of sample data and the ability to handle high-dimensional data, the random forest algorithm was used to construct a seawater intrusion suppression model and was combined with a genetic algorithm. The critical river discharge for suppressing estuary seawater intrusion determined using this model. The critical river discharge was found to gradually increase with the maximum tidal range, which in three different tide scenarios was 487 m3/s, 493 m3/s, and 531 m3/s. The practicable seawater intrusion suppression scheme was built up with three phases to make it easier to regulate upstream reservoirs. In the scheme, the initial reading of river discharge was 490 m3/s, and it rose to 650 m3/s over six days, from four days before the high tide's arrival to two days following it, and before falling down to 490 m3/s at the end. Verified with the 16 seawater intrusion events in the five dry years, this scheme could eliminate 75% of the seawater intrusion risk and effectively reduce the chlorine level for the remaining 25% of events.

Spatial patterns of diffusive greenhouse gas emissions from cascade hydropower reservoirs

Greenhouse gas (GHG) emissions from reservoirs have received increasing attention in recent years. Despite extensive studies in single reservoirs, GHG emission patterns in cascades of multiple reservoirs, which are becoming increasingly common worldwide, remain unknown. This study investigated the spatial patterns of diffusive carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) emissions, as well as their total CO2-equivalent (CO2-eq), for a cascade hydropower system in the heavily dammed upper Mekong River, China. Results demonstrated that GHG emissions in cascade reservoirs were higher than that in the upstream channel since the accumulated sediments fueled microbes for GHG production. In cascade reservoirs, CO2 made the largest contribution (58.6%–84.8%) to total CO2-eq, while the contribution of N2O was marginal. Deep reservoirs emitted less CO2, which was attributed to higher CO2 consumption by phytoplankton. Reservoirs formerly occupying the most upstream position for the longest period of time in the cascade emitted the most CH4, perhaps due to accumulations of river borne sediments. The total CO2-eq generally increased with distance downstream except within deep reservoirs. These findings indicate that, with respect to mitigating GHG emissions, the deepest, most upstream reservoir should be constructed first in the configuration of cascade hydropower reservoirs, and less sediment will enter downstream reservoirs, which have higher CO2-eq emissions.

Application of deep learning algorithms to confluent flow-rate forecast with multivariate decomposed variables

Study regionSong bengue confluent in Cameroon regulates the river flow rate for hydro energy production with input from four upstream reservoirs. Study focusDeep learning models forecast a day flow rate of the Song bengue confluent. Decomposed time series multivariate variables of flow rate, precipitation, and upstream reservoir inflows, outflows, and precipitation are used. Different windows and horizons for the forecast are analyzed using deep learning models. A comparative study among the models is carried out. Input parameters are decomposed and different partitions are used as scenarios for the best partition. New hydrological insightA 7-day window and 1-day forecast yield the lowest error. The dense model is the best among the models followed by the Long-short term memory (LSTM) model, and lastly, the one-dimensional convolutional neural network (Conv1D) based on mean absolute error (MAE), mean square error (MSE), root mean squared error (RMSE), and Nash Sutcliff Efficiency (NSE). Using the scenario with all decomposed variables produces the best result with about a 50% difference in error margin. The second-best result is obtained by using only undecomposed data. The remainder component should not be ignored as it contains important hydrological information.

Blooms and flows: Effects of variable hydrology and management on reservoir water quality

AbstractFlow management has the potential to significantly affect ecosystem condition. Shallow lakes in arid regions are especially susceptible to flow management changes, which can have important implications for the formation of cyanobacterial blooms. Here, we reveal water quality shifts associated with changing source water inflow management. Using in situ monitoring data, we studied a seven‐year time span during which inflows to a shallow, eutrophic drinking water reservoir transitioned from primarily natural landscape runoff (2014–2015) to managed flows from a larger upstream reservoir (Lake Diefenbaker; 2016–2020) and identified significant changes in cyanobacteria (as phycocyanin) using generalized additive models to classify cyanobacterial bloom formation. We then connected changes in water source with shifts in chemistry and the occurrence of cyanobacterial blooms using principal components analysis. Phycocyanin was greater in years with managed reservoir inflow from a mesotrophic upstream reservoir (2016–2020), but dissolved organic matter (DOM) and specific conductivity, important determinants of drinking water quality, were greatest in years when landscape runoff dominated lake water source (2014–2015). Most notably, despite changing rapidly, it took multiple years for lake water to return to a consistent and reduced level of DOM after managed inflows from the upstream reservoir were resumed, an observation that underscores how resilience may be hindered by weak resistance to change and slow recovery. Environmental flows for water quality are rarely defined, yet we show that trade‐offs exist between poor water quality via elevated conductivity and DOM and higher bloom risk, depending on water source. Our work highlights the importance of source water quality, not just quantity, to water security, and our findings have important implications for water managers who must protect ecosystem services while adapting to projected hydroclimatic change.

Optimum reservoir operation of a networking reservoirs system using conditional atom search optimization and a conditional genetic algorithm

This study aimed to apply conditional atom search optimization (CASO) for searching optimum rule curves in a networking reservoirs system with a reservoir simulation model. The networking reservoirs system consisted of 5 reservoirs located in Sakon Nakhon Province, Thailand. The efficiency of the new optimum rule curves was determined by comparison of operating systems between a single reservoir and a networking reservoirs system. The results displayed circumstances of scarcity and excess of water. Where the circumstances of scarcity are frequency and duration. Whilst, excesses of water are average water and the highest water. In addition, the efficiency of searching for optimum rule curves was compared between conditional genetic algorithm (CGA) and CASO techniques. The new optimum rule curves from the networking reservoirs system had an average excess water of 43.828 MCM/year. This average excess water was less than that found for optimum curves from the single system in which the average excess of water was 45.602 MCM/year. CASO was more efficient in converging optimum rule curve solutions faster than CGA by 40.00%. In conclusion, the CASO can be used to search for optimum networking reservoirs rule curve solutions effectively. For the networking reservoirs system derived water from the upstream reservoirs, an analysis was performed of the downstream reservoir. The results showed that the optimum rule curves using CASO operated as a networking reservoirs system provided higher efficiency than a single reservoir system. In addition, they reduced the amount of time that water exceeded the river capacity at a downstream weir by one month compared with the original period of two months.

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.