Reservoir Outflow Research Articles

A Guide to Breach Prediction

Earthen embankments that are categorised as large (15m or greater in height) number in the tens of thousands globally. Embankment dam risk assessment is a vital measure that has been adopted throughout the industry to assess the potential impact that catastrophic dam failures can carry. A critical part of this assessment is the prediction of the breach process, which will determine the reservoir outflow hydrograph. This is crucial for the following stage of flood routing, which aids in flood risk assessment, evacuation planning and land-use planning. This report provides details of the breach prediction methods available to users, ranging from simple parametric equations to complex multi-dimensional erosion models. These are commonly divided into three categories; parametric models, semi-physically based models and physically based models. Parametric models, such as Froehlich (2016a, b), Xu & Zhang (2009) and Von Thun & Gillette (1990), allow breach geometry, formation time and peak outflow to be estimated through the regression analysis of historical dam failure data. These have advantages in their ease and speed of use, but were found to have great uncertainty in their application and are therefore not typically suitable for high risk applications, where uncertainties will have a large impact. Appropriate applications include initial appraisal-level breach modelling and the study of low-risk scenarios where uncertainties will have a minimal impact. Semi-physically based models, such as HEC-RAS, take breach geometry and formation time, or soil erosion rates, as input values to produce a breach hydrograph. No physical processes are modelled; rather the flow of water through the use-defined breach is calculated using simple fluid dynamic equations, such as weir and orifice flow. These provide no improvement in the accuracy of predicting a breach over parametric models, but improve on the process of converting these results into outflow hydrographs, which may be required for further use. Physically based models, such as EMBREA, DL Breach and WinDAM consider the complex geotechnical, structural and hydraulic behaviour of an embankment dam and its impounded reservoir. While generally more time-consuming than parametric and semi-physical models, physical models tend to provide results with a greater certainty and accuracy. These, as a whole, are suitable for high risk breach scenarios, where accuracy and reliability are critical in providing results within the acceptable bounds of uncertainty. The descriptions and recommendations of breach prediction methods in this report are intended to guide users towards the most appropriate breach model for a given scenario. A recommended approach to choosing a model type (parametric, physical etc.) is given, taking into consideration the type of analysis and associated risks, amongst other factors. It was concluded that, while parametric models have tended to be used by industry in the past, technological advancements and practical field testing have allowed rigorous physically based models methods to become more feasible. Further developments are likely to reduce the reliance of physical models on simplifications and improve their accuracy and usability.

The Value of Hydrologic Information in Reservoir Outflow Decision-Making

The controlled outflows from a reservoir are highly dependent on the decisions made by the reservoir operators who mainly rely on available hydrologic information, such as past outflows, reservoir water level and forecasted inflows. In this study, Random Forests (RF) algorithm is used to build reservoir outflow simulation model to evaluate the value of hydrologic information. The Three Gorges Reservoir (TGR) in China is selected as a case study. As input variables of the model, the classic hydrologic information is divided into past, current and future information. Several different simulation models are established based on the combinations of these three groups of information. The influences and value of hydrologic information on reservoir outflow decision-making are evaluated from two different perspectives, the one is the simulation result of different models and the other is the importance ranking of the input variables in RF algorithm. Simulation results demonstrate that the proposed model is able to reasonably simulate outflow decisions of TGR. It is shown that past outflow is the most important information and the forecasted inflows are more important in the flood season than in the non-flood season for reservoir operation decision-making.

Sustainable Management of Reservoir Water Quality and Quantity Through Reservoir Operational Strategy and Watershed Control Strategies

Water quality impairment is a serious health concern for reservoirs; two strategies were used to control reservoir outflow quality: (1) control of reservoir inflows with implementation of structural best management practices (BMPs) at the watershed, and (2) management of reservoir outflows by reservoir operational strategy. To assess the effectiveness of two strategies on reservoir water quality, an extension of the Sustainability Index (SI) for water quality was defined. Additionally, a quantity-based SI for supplying of downstream water demands was defined. So il and water assessment tool was linked to a reservoir simulation model (CE-QUAL-W2), and coupled with multi-objective particle swarm optimization algorithm. The proposed model was applied in four different scenarios on Alavian reservoir and its watershed, in Iran, during a 6-year time horizon. Four BMPs, named detention ponds, filter strips, parallel terraces, and grade stabilization structures, were used. The results indicated that application of the proposed approach provides the best set of solutions for decision makers to manage outflow quality and quantity. Whenever the watershed management strategy is not possible/practical, the reservoir operational strategy in selective withdrawal scheme would improve reservoir outflow quality by up to 77%. On the other hand, when the reservoir downstream water demand satisfaction is necessary, the watershed management strategy, or selective withdrawal scheme would be improved when the reservoir outflow dissolved oxygen concentration SI by up to 30 and 52%, respectively. Among the applied BMPs, filter strip had more effect on reducing nutrient loads and it was the most chosen BMP.

Hydrological drought index based on reservoir capacity – Case study of Batujai dam in Lombok Island, West Nusa Tenggara, Indonesia

AbstractHydrological drought index analysis has been widely developed and applied for the development of water resources. The island of Lombok, which is largely a dry land, requires a significant hydrological drought index to be sourced from measurable data analysis. This research focused aims to obtain hydrological drought index in Lombok Island using the capacity change of reservoir. The analysis includes reservoir data especially in the event of El-Nino. The main parameters analysed in this work are data homogeneity, decrease line of reservoir volume, increase in the line of reservoir volume, reservoir volume deficit, and hydrological drought index (RDI). The basic equation uses the water balance in the reservoir, which is the inflow–outflow and change of reservoir. The results of the analysis show that in the event of El-Nino, the drought hydrological index indicates different levels depending upon the water level of the reservoir. The criteria for the drought level are as follows: weak RDI = from −0.46 to −0.01 at an reservoir elevation of 90.88 to 92.33 m a.s.l, moderate RDI: from −0.59 to −0.46 at water level of reservoir from 90.27 to 90.88 m a.s.l, sever RDI: from −0.80 to −0.59 at water level of reservoir from 88.83 to 90.27 m a.s.l. and very severe RDI: from −0.89 to −0.80 at water level of water reservoir 87.78–88.83 m a.s.l. The duration of drought was 9 months, i.e., from February to November.

Comparison of runoff and river flow in two large northern basins

AbstractThe magnitude and timing of water delivery in two large northern basins are analysed to clarify where runoff is generated and how their rivers acquire comparable regimes (or seasonal rhythms) of flow. These two rivers, the Mackenzie in Canada and the Yenisei in Russia, traverse similar latitudes, physiographic provinces, vegetation zones and climatic regions. Within the basins, mountainous terrain and high-precipitation sections usually yield large runoff, but low runoff comes from the plains, low plateaus and areas of aridity. Winter runoff is commonly low and snowmelt is responsible for annual peak runoff in most parts of these basins, though rainfall is a prominent runoff source in southern Yenisei. Many rivers in the drainage networks display a seasonal pattern that suggests the dominance of snowmelt to produce a spring freshet followed by a general decline in summer that diminishes to winter low flows. Regulation of reservoir outflow greatly distorts the natural flow regime. Yet, along the main river downstream of the reservoirs, the influx of tributary discharge can dilute such human influence. To truly understand how water is produced and transferred in large northern rivers, the spatial and temporal complexity of flow-generation mechanisms and storage effects need to be unravelled.

Hydrological modelling in the anthroposphere: predicting local runoff in a heavily modified high-alpine catchment

Hydrological models within inflow forecasting systems for high-alpine hydropower reservoirs can provide valuable information as part of a decision support system for the improvement of hydropower production or flood retention. The information, especially concerning runoff, is however rarely available for the calibration of the hydrological models used. Therefore, a method is presented to derive local runoff from secondary information for the calibration of the model parameters of the rainfallrunoff model COSERO. Changes in water levels in reservoirs, reservoir outflows, discharge measurements at water intakes and in transport lines are thereby used to derive the local, “natural” flow for a given sub-catchment. The proposed method is applied within a research study for the ÖBB Infrastructure Railsystem division in the Stubache catchment in the central Austrian Alps. Here, the ÖBB operates the hydropower scheme “Kraftwerksgruppe Stubachtal”, which consists of 7 reservoirs and 4 hydropower stations. The hydrological model has been set up considering this human influences and the high natural heterogeneity in topography and land cover, including glaciers. Overall, the hydrological model performs mostly well for the catchment with highest NSE values of 0.78 for the calibration and 0.79 for the validation period, also considering the use of homogeneous parameter fields and the uncertainty of the derived local discharge values. The derived runoff data proved to be useful information for the model calibration. Further analysis, examining the water balance and its components as well as snow cover, showed satisfactory simulation results. In conclusion, a unique runoff dataset for a small scale high-alpine catchment has been created to establish a hydrological flow prediction model which in a further step can be used for improved and sustainable hydropower management.

Quantifying human impacts on hydrological drought using a combined modelling approach in a tropical river basin in central Vietnam

Abstract. Hydrological droughts are one of the most damaging disasters in terms of economic loss in central Vietnam and other regions of South-east Asia, severely affecting agricultural production and drinking water supply. Their increasing frequency and severity can be attributed to extended dry spells and increasing water abstractions for e.g. irrigation and hydropower development to meet the demand of dynamic socioeconomic development. Based on hydro-climatic data for the period from 1980 to 2013 and reservoir operation data, the impacts of recent hydropower development and other alterations of the hydrological network on downstream streamflow and drought risk were assessed for a mesoscale basin of steep topography in central Vietnam, the Vu Gia Thu Bon (VGTB) River basin. The Just Another Modelling System (JAMS)/J2000 was calibrated for the VGTB River basin to simulate reservoir inflow and the naturalized discharge time series for the downstream gauging stations. The HEC-ResSim reservoir operation model simulated reservoir outflow from eight major hydropower stations as well as the reconstructed streamflow for the main river branches Vu Gia and Thu Bon. Drought duration, severity, and frequency were analysed for different timescales for the naturalized and reconstructed streamflow by applying the daily varying threshold method. Efficiency statistics for both models show good results. A strong impact of reservoir operation on downstream discharge at the daily, monthly, seasonal, and annual scales was detected for four discharge stations relevant for downstream water allocation. We found a stronger hydrological drought risk for the Vu Gia river supplying water to the city of Da Nang and large irrigation systems especially in the dry season. We conclude that the calibrated model set-up provides a valuable tool to quantify the different origins of drought to support cross-sectorial water management and planning in a suitable way to be transferred to similar river basins.

Simulation of Outflow Reservoir Level, and Hydro-Power at Dukan Dam Using Artificial Neural Network

Simulation of Outflow Reservoir Level, and Hydro-Power at Dukan Dam Using Artificial Neural Network

Multi-Stage Dynamic Programming Method for Short-Term Cascade Reservoirs Optimal Operation with Flow Attenuation

In Short-term Cascade Reservoirs Optimal Operation (SCROO), the flow from upstream reservoir to downstream reservoir which propagates in the natural channel can be generalized as not only transposition but also attenuation. In order to get the relative accurate inflow series of downstream reservoir, the paper tries to adopt the Muskingum model to simulate the inflow of the downstream reservoir instead of the easier processing in most papers of SCROO: ignoring the flow attenuation in natural channel. Considering the flow attenuation between the cascade reservoirs, the SCROO problem do not satisfy the “Principe of Optimality” anymore, so the Dynamic Programming(DP) is no longer applicable. The paper proposes a new improved DP named Multi-Stage Dynamic Programming (MSDP) based on DP. In MSDP, multi-stage’s outflow of upstream reservoir is taken into account at the same time and then inflow of downstream reservoir can be calculated by the Muskingum model, which can include much more flow information than the easier processing with DP, and the inflow of downstream reservoir will be closer to the actual one. The paper takes the cascade hydro-power stations consisting of Jindong and Guandi in Yalong river basin as an example to solve the SCROO problem with MSDP. By comparing the operation result of MSDP and DP with the easier processing, the operation strategy of MSDP can gain further benefits than DP’s in actual operation.

Damming effects on dissolved inorganic carbon in different kinds of reservoirs in Jialing River, Southwest China

To assess the effects of river damming on dissolved inorganic carbon in the Jialing River, a total of 40 water samples, including inflow, outflow, and stratified water in four cascade reservoirs (Tingzikou, Xinzheng, Dongxiguan, Caojie) were collected in January and July, 2016. The major cations, anions, and δ13CDIC values were analyzed. It was found that the dissolved compositions are dominated by carbonate weathering, while sulfuric acids may play a relatively important role during carbonate weathering and increasing DIC concentration. Different reservoirs had variable characteristics of water physiochemical stratification. The DIC concentrations of reservoir water were lower in summer than those in winter due to the dilute effects and intensive aquatic photosynthesis, as well as imported tributaries. The δ13CDIC values in Tingzikou Reservoir were higher during summer than those in winter, which indicated that intensive photosynthesis increased the δ13CDIC values in residual water, but a similar trend was not obvious in other reservoirs. Except for in Xinzheng Reservoir, the δ13CDIC values in inflow and outflow reservoir water were lower than those in the surface water of stratified sampling in summer. For stratified sampling, it could be found that, in summer, the Tingzikou Reservoir δ13CDIC values significantly decreased with water depth due to the anaerobic breakdown of organic matter. The significant correlation (p < 0.01 or 0.05) between the DIC concentrations, the δ13CDIC values and anthropogenic species (Na++K+, Cl–, \({\text{SO}}_{4}^{2 - }\)and \({\text{NO}}_{3}^{ - }\)) showed that the isotope composition of DIC can be a useful tracer of contaminants. In total, Tingzikou Reservoir showed lacustrine features, Xinzheng Reservoir and Dongxiguan Reservoir had “transitional” features, and Caojie Reservoir had a total of “fluvial” features. Generally, cascade reservoirs in the Jialing River exhibited natural river features rather than typical lake features due to characteristics of reservoir water in physiochemical stratification, spatiotemporal variations of DIC concentrations and isotopic compositions. It is evident that the dissolved inorganic carbon dynamics of natural rivers had been partly remolded by dam building.

Modifying the downstream hydrograph with staged labyrinth weirs

Labyrinth and piano key weirs are hydraulically more efficient than linear weirs of common width. As the spillway discharge efficiency increases, the required reservoir detention volume reserved for flood routing reduces and the maximum base-flow operating reservoir pool elevation can subsequently be increased (additional water storage) without a reduction in dam safety. Increased spillway discharge efficiency also causes the reservoir outflow hydrograph to compress temporally and increases the peak outflow discharge, potentially increasing downstream flooding impacts. The influence of linear, labyrinth, and staged labyrinth weir (i.e. cycles with different crest elevations) head-discharge characteristics on the outflow hydrograph behavior were evaluated by numerically routing various flood discharges through a reservoir; peak outflow discharges, the maximum water surface elevation, and the required detention volumes were quantified for each weir alternative. In addition to the benefit of isolating base flows to a subset of the labyrinth weir, the staged labyrinth weir proved to be an effective alternative for modifying (decreasing) the spillway discharge efficiency to limit downstream flooding impact for higher-frequency return-period storm events.

Flow forecasting in multiple sections of a river system

A river system includes the combination of flows occurring simultaneously in the main river and its contributing tributaries. Any change in the flow condition of the river system is caused due to changes in flow of the main river and/or contributing tributaries. An accurate flow forecasting at multiple sections of a river system is worthy for issuing early warning to the imminent floods and in regulating the reservoir outflows. The application of multiple-inputs and multiple-outputs (MIMO) model is an effective way for simultaneous flow forecasting as it provides interrelation among multiple input and multiple output variables simultaneously. In the present study an Artificial Neural Networks (ANN) based MIMO model has been developed for Barak river system in Assam, India using Partially Recurrent Neural Network (PRNN) and Nonlinear Autoregressive with Exogenous Inputs (NARX) approaches. Performance of the model using both NARX and PRNN provide an efficacy with coefficient of efficiency (CE) > 0.87 and Mean Absolute Percentage Error (MAPE) < 7.66% at 12 hour lead time forecasting. This indicates satisfactory model performances for simultaneous flow forecasting at multiple sections of a river system however the results obtained by MIMO using NARX (MIMONARX) perform better than MIMO using PRNN (MIMO-PRNN) in terms of statistical performance criterion.

Comparison of static and dynamic resilience for a multipurpose reservoir operation

AbstractReliability, resilience, and vulnerability are the traditional risk measures used to assess the performance of a reservoir system. Among these measures, resilience is used to assess the ability of a reservoir system to recover from a failure event. However, the time‐independent static resilience does not consider the system characteristics, interaction of various individual components and does not provide much insight into reservoir performance from the beginning of the failure event until the full performance recovery. Knowledge of dynamic reservoir behavior under the disturbance offers opportunities for proactive and/or reactive adaptive response that can be selected to maximize reservoir resilience. A novel measure is required to provide insight into the dynamics of reservoir performance based on the reservoir system characteristics and its adaptive capacity. The reservoir system characteristics include, among others, reservoir storage curve, reservoir inflow, reservoir outflow capacity, and reservoir operating rules. The reservoir adaptive capacity can be expressed using various impacts of reservoir performance under the disturbance (like reservoir release for meeting a particular demand, socioeconomic consequences of reservoir performance, or resulting environmental state of the river upstream and downstream from the reservoir). Another way of expressing reservoir adaptive capacity to a disturbing event may include aggregated measures like reservoir robustness, redundancy, resourcefulness, and rapidity. A novel measure that combines reservoir performance and its adaptive capacity is proposed in this paper and named “dynamic resilience.” The paper also proposes a generic simulation methodology for quantifying reservoir resilience as a function of time. The proposed resilience measure is applied to a single multipurpose reservoir operation and tested for a set of failure scenarios. The dynamic behavior of reservoir resilience is captured using the system dynamics simulation approach, a feedback‐based object‐oriented method, very effective for modeling complex systems. The results of dynamic resilience are compared with the traditional performance measures in order to identify advantages of the proposed measure. The results confirm that the dynamic resilience is a powerful tool for selecting proactive and reactive adaptive response of a multipurpose reservoir to a disturbing event that cannot be achieved using traditional measures. The generic quantification approach proposed in the paper allows for easy use of dynamic resilience for planning and operations of various civil infrastructure systems.

DEVELOPMENT OF RESERVOIR OPERATION FOR BATANG AI HYDROELECTRIC PROJECT

Batang Ai Hydroelectric Project is meant to generate electricity. The Batang Ai Dam has a maximum capacity to generate around 108MW when it is fully operational. Efficient reservoir operation should be carried out very carefully in order to provide reliable water supply for power generation and water demand. The research of this project is to review the Batang Ai Dam storage conservation for the reservoir operation by using storage conservation simulation. The simulations are carried out with various outflow conditions using the principle of the storage equation. Lastly, the results from the simulation show that with proper regulation of the reservoir outflow, the Batang Ai Hydroelectric Project reliability to provide continuous power supply without shortage in water supply is assured.

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.

An Experiment on Risk-Based Decision-Making in Water Management Using Monthly Probabilistic Forecasts

Abstract The use of probabilistic forecasts is necessary to take into account uncertainties and allow for optimal risk-based decisions in streamflow forecasting at monthly to seasonal lead times. Such probabilistic forecasts have long been used by practitioners in the operation of water reservoirs, in water allocation and management, and more recently in drought preparedness activities. Various studies assert the potential value of hydrometeorological forecasting efforts, but few investigate how these forecasts are used in the decision-making process. Role-playing games can help scientists, managers, and decision-makers understand the extremely complex process behind risk-based decisions. In this paper, we present an experiment focusing on the use of probabilistic forecasts to make decisions on reservoir outflows. The setup was a risk-based decision-making game, during which participants acted as water managers. Participants determined monthly reservoir releases based on a sequence of probabilistic inflow forecasts, reservoir volume objectives, and release constraints. After each decision, consequences were evaluated based on the actual inflow. The analysis of 162 game sheets collected after eight applications of the game illustrates the importance of leveraging not only the probabilistic information in the forecasts but also predictions for a range of lead times. Winning strategies tended to gradually empty the reservoir in the months before the peak inflow period to accommodate its volume and avoid overtopping. Twenty percent of the participants managed to do so and finished the management period without having exceeded the maximum reservoir capacity or violating downstream release constraints. The role-playing approach successfully created an open atmosphere to discuss the challenges of using probabilistic forecasts in sequential decision-making.

Simulating California reservoir operation using the classification and regression‐tree algorithm combined with a shuffled cross‐validation scheme

AbstractThe controlled outflows from a reservoir or dam are highly dependent on the decisions made by the reservoir operators, instead of a natural hydrological process. Difference exists between the natural upstream inflows to reservoirs and the controlled outflows from reservoirs that supply the downstream users. With the decision maker's awareness of changing climate, reservoir management requires adaptable means to incorporate more information into decision making, such as water delivery requirement, environmental constraints, dry/wet conditions, etc. In this paper, a robust reservoir outflow simulation model is presented, which incorporates one of the well‐developed data‐mining models (Classification and Regression Tree) to predict the complicated human‐controlled reservoir outflows and extract the reservoir operation patterns. A shuffled cross‐validation approach is further implemented to improve CART's predictive performance. An application study of nine major reservoirs in California is carried out. Results produced by the enhanced CART, original CART, and random forest are compared with observation. The statistical measurements show that the enhanced CART and random forest overperform the CART control run in general, and the enhanced CART algorithm gives a better predictive performance over random forest in simulating the peak flows. The results also show that the proposed model is able to consistently and reasonably predict the expert release decisions. Experiments indicate that the release operation in the Oroville Lake is significantly dominated by SWP allocation amount and reservoirs with low elevation are more sensitive to inflow amount than others.

Simulating Human Water Regulation: The Development of an Optimal Complexity, Climate-Adaptive Reservoir Management Model for an LSM

Abstract The widespread influence of reservoirs on global rivers makes representations of reservoir outflow and storage essential components of large-scale hydrology and climate simulations across the land surface and atmosphere. Yet, reservoirs have yet to be commonly integrated into earth system models. This deficiency influences model processes such as evaporation and runoff, which are critical for accurate simulations of the coupled climate system. This study describes the development of a generalized reservoir model capable of reproducing realistic reservoir behavior for future integration in a global land surface model (LSM). Equations of increasing complexity relating reservoir inflow, outflow, and storage were tested for 14 California reservoirs that span a range of spatial and climate regimes. Temperature was employed in model equations to modulate seasonal changes in reservoir management behavior and to allow for the evolution of management seasonality as future climate varies. Optimized parameter values for the best-performing model were generalized based on the ratio of winter inflow to storage capacity so a future LSM user can generate reservoirs in any grid location by specifying the given storage capacity. Model performance statistics show good agreement between observed and simulated reservoir storage and outflow for both calibration (mean normalized RMSE = 0.48; mean coefficient of determination = 0.53) and validation reservoirs (mean normalized RMSE = 0.15; mean coefficient of determination = 0.67). The low complexity of model equations that include climate-adaptive operation features combined with robust model performance show promise for simulations of reservoir impacts on hydrology and climate within an LSM.

牛栏江红石岩堰塞湖整治工程施工期出、入库洪水量平衡分析

为给2016年汛期堰塞体整治、溢洪洞、发电厂房和库区复建交通隧道等项目施工的防洪度汛工作提供决策依据，最大限度减轻施工期间的洪灾风险，根据堰塞湖坝址各设计标准的入库洪水过程、原红石岩电站引水隧洞和溢洪洞联合泄流曲线及堰塞湖库容曲线，分析了当堰塞湖发生200、100、50、30、20、10、5年一遇洪水时，堰塞湖的洪水下泄和库水位变化情况，并选取了2015年汛期发生的三场洪水进行水量平衡分析。分析表明：2015年堰塞湖出、入库水量平衡性较好，实际下泄流量与泄流曲线及天生桥站的水位、流量关系符合性较好，洪水下泄通畅，安全可控。原红石岩电站引水隧洞和右岸溢洪洞(上半洞)能够合并下泄200a一遇以下标准的洪水，坝前水位低于堰塞体泄流槽底部高程。 Analysis is done on the discharge of flood and variation of water level in the reservoir at the barrier lake in case of 5-year, 10-year, 20-year, 30-year, 50-year, 100-year and 200-year flood according to reservoir inflow flood process under various design standards at the dam site of the barrier lake, the discharge curve of combination of diversion tunnel and spillway tunnel of the former Hongshiyan HPP, and the ca-pacity curve of the barrier lake reservoir, in order to provide decision basis for flood control in barrier regulation, construction of spillway tunnels, power plants and reconstruction of traffic tunnels in the re-servoir area in the flood season in 2016, and to minimize the flood risk during construction. And three flood events occurring during the flood season in 2015 are selected for water balance analysis. The anal-ysis shows that the reservoir outflow and inflow at the barrier lake in 2015 are well balanced, the actual discharge flow and discharge curve are well consistent with the water level and flow at Tianshengqiao HPP, and the flood is discharged without blockage and is controlled safely. The diversion tunnel from the former Hongshiyan HPP and the spillway tunnel (upper part) on the right bank can jointly discharge flood below standard of the 200-year flood. The water level before the dam is lower than the elevation of the bottom of the sluice channel of the barrier.

The Impact of Drought on Streamflow and Stream-Aquifer Exchange in the Upper Neosho River, Kansas

Meteorological drought in the Great Plains of the U.S. has a significant influence on the hydrology of small drainage basins. Its effect on local surface water and groundwater systems is complicated when streamflow is regulated by flood-control reservoirs. An analysis of local precipitation, discharge, and groundwater records on annual, monthly, and daily intervals in the upper Neosho River of Kansas demonstrates the importance of frequent, small-scale monitoring to resource management. Natural, drought-induced, noflow conditions prior to reservoir construction were eliminated by sustained, low-volume, reservoir outflow over five drought cycles. Temporary bank storage, caused by reservoirinduced, high-flow pulses, was observed at the Emporia State University Campus Woods field station during a prolonged recent drought. Gaining and losing stream conditions were observed in multi-year monitoring but, in drought years, losing conditions occurred only when reservoir releases generated stream flow. In drought and non-drought years, relatively low groundwater levels coincided with seasonal growing periods, reflecting the importance of transpiration by riparian vegetation on stream-aquifer exchange. An understanding of the drought response of the individual elements of a floodplain hydrologic system is important to management of the integrated resource.