Optimization and risk analyses for rule curves of reservoir operation: application to Tien-Hua-Hu Reservoir in Taiwan.

Tien-Hua-Hu Reservoir is currently under planning by the Water Resources Agency, Taiwan to meet the increasing water demands of central Taiwan arising from rapid growth of domestic water supply, and high-tech industrial parks. This study develops a simulation model for the ten-day period reservoir operation to calculate the ten-day water shortage index under varying rule curves. A genetic algorithm is coupled to the simulation model to find the optimal rule curves using the minimum ten-day water shortage index as an objective function. This study generates many sets of synthetic streamflows for risk, reliability, resiliency, and vulnerability analyses of reservoir operation. ARMA and disaggregation models are developed and applied to the synthetic streamflow generation. The optimal rule curves obtained from this study perform better in the ten-day shortage index when compared to the originally designed rule curves from a previous study. The optimal rule curves are also superior to the originally designed rule curves in terms of vulnerability. However, in terms of reliability and resiliency, the optimal rule curves are inferior to the those originally designed. Results from this study have provided in general a set of improved rule curves for operation of the Tien-Hua-Hu Reservoir. Furthermore, results from reliability, resiliency and vulnerability analyses offer much useful information for decision making in reservoir operation.     

基于Copula函数的三峡库区万州段蓄水前后降雨量-径流量关系分析

三峡水库蓄水对其库区降雨量-径流量关系变化的影响程度对于库区水资源规划有着重要意义。选用万县水文站1977-2017共计41 a的降雨量和径流量实测值,确定了各蓄水阶段降雨量和径流量的分布情况,引入Copula函数模型计算各阶段的联合分布函数,定量分析水库调蓄对两者关系的影响,预测了2017年后水文情势。结果表明：采用Copula函数联合分布数学模型能较好计算三峡库区万州段不同阶段的降雨量-径流量关系。万州段从天然河道变为库区河道后,降雨量-径流量关系发生了较大变化。在天然河道阶段,降雨量和径流量均采用皮尔逊III型分布最为合理;三峡水库工程施工期和初步蓄水阶段,降雨量变为Gumbel分布,径流量变为对数正态分布;试验性蓄水阶段,降雨量变为对数正态分布,径流量恢复至皮尔逊III型分布。年降雨量和年径流量在施工期及初步蓄水阶段较天然河道阶段均有所减少,年降雨量变幅区间减小38.4%,年径流量变幅区间减小20.6%;试验性蓄水阶段的年降雨量增多,变幅区间增大24.5%,而年径流量减少,变幅区间减小57%。通过该数学模型预测三峡库区万州段今后年径流量不小于3 490×10⁸ m³（±5%）,最大不超过4 055×10⁸ m³（±5%）;年降雨量不小于1 048 mm（±5%）,最大值不超过1 842 mm（±5%）。该研究可为三峡库区万州段流域水资源开发利用与水文序列的重构工作等提供科学依据,也可为其他库区内河道的水文特性变化关系的研究提供参考。     

Impact assessment of reservoir desiltation measures for downstream riverbed migration in climate change: A case study in northern Taiwan

Typhoon Aere in 2004 induced severe sedimentation and loss of storage capacity of the Shihmen Reservoir in northern Taiwan. The resulting dramatic increase in the turbidity of the water seriously affected the water supply. To effectively maintain the stability of the water supply and maintain the reservoir’s storage capacity, the government of Taiwan began to plan and construct a series of improvement measures, such as a sediment flushing tunnel, the JhongJhuang Bank-Side Reservoir, and the Amuping Desilting Tunnel. However, previous studies only focused on the impact of the sediment flushing tunnel and the Amuping Desilting Tunnel on the downstream riverbed, and did not consider the possibility of increasing sediment discharge after the completion of the JhongJhuang Bank-Side Reservoir. In addition, climate change will cause the intensity of extreme rainfall to increase enormously in the future. That rainfall and extra sediment flushing will challenge the existing flood prevention facilities. Therefore, this study considered that the JhongJhuang Bank-Side Reservoir will increase sediment discharge of the Shihmen Reservoir, and used dynamical downscaling extreme typhoon data of climate change under the RCP 8.5 scenario to explore the flood prevention and riverbed migration of the main channels of the Dahan and Tamsui Rivers in the future. We used the rainfall–runoff model of Hydrologic Modeling System to simulate rainfall and runoff, and used the hydraulic and sediment transport model of CCHE1D to holistically simulate flood events and consequent river scouring and deposition behaviors. Our results showed that the projected peak discharge during the late 21st century (2075 to 2099) will be at least 50% higher than that during the baseline (1979 to 2003) period. In terms of flood prevention, the potential of overbank flooding will increase in the downstream area, and the trend of long-term change in the riverbed will be dominated by degradation (-0.489 ± 0.743 m) in the future. The improvement measures will have a limited impact on riverbed migration (0.011 ± 0.094 m) in the Dahan and Tamsui Rivers. After the operation of the JhongJhuang Bank-Side Reservoir, the Shihmen Reservoir is expected to increase the sediment discharge ratio by 70% during floods, and it will not cause excessive water turbidity that may affect downstream water supply.     

Reservoir Operation Incorporating Hedging Rules and Operational Inflow Forecasts

Reservoir operation incorporating a naïve hedging strategy and operational inflow forecasting is studied in this paper. Gridded precipitation forecasts from climate model, ECHAM4.5, are used as potential predictors for reservoir inflow forecasting. In building a statistical predicting model, principal component analysis (PCA) is used to reduce the dimension of the regression model. Performance evaluation indices, including water supply satisfaction ratio, environmental flow satisfaction ratio, end-of-month storage satisfaction ratio and flood prevention capacity index, are defined. Three scenarios where a naïve hedging operation rule under different set of reservoir inflow are investigated. These are evaluated for a water supply reservoir, Falls Lake Reservoir, at Neuse River in the southeast United State. Reservoir simulation with monthly average inflow serves as a benchmark. The utility of operational inflow forecasts is quantified by the improvements of performance indices. Results show that reservoir operation under perfect inflow forecasting has the highest values for most indices. Compared to climatology, operational inflow forecasts result in higher index values. Among all the performance indices, end-of-month storage satisfaction ratio is the most sensitive index to inflow information. Limitation of this study and further work is also discussed.     

近期黄河上游气候变化对龙羊峡入库水量的影响

根据1956年以来气候资料,统计分析了黄河上游龙羊峡以上地区气温、降水分布规律及变化特点,并以各站气温、降水与唐乃亥站天然径流量关系为基础,建立天然径流量计算公式,计算分析了唐乃亥以上地区20世纪90年代(近期)以来气候变化对龙羊峡入库径流量的影响,以及唐乃亥站径流量对气候变化的敏感性.结果表明:①近期唐乃亥以上各区年平均气温均较常年平均偏高0.5℃左右,而比前期升温达0.7~0.8℃;降水量不仅较多年均值偏少,更比前期显著减少,其中玛曲一带最大减幅达15.8%;②平均天然年径流量与前期相比,近期减少了43.7亿m3,表明气候变化所引起的减幅达20.2%;③龙羊峡入库径流量对降水变化的响应要比气温更为显著.     

Climate Variability Influences on Hydrological Responses of a Large Himalayan Basin

The hydrological cycle, a fundamental component of climate is likely to be altered in important ways due to climate change. In this study, the historical daily runoff has been simulated for the Chenab River basin up to Salal gauging site using a simple conceptual snowmelt model (SNOWMOD). The model has been used to study the impact of plausible hypothetical scenarios of temperature and rainfall on the melt characteristics and daily runoff of the Chenab River basin. The average value of increase in snowmelt runoff for T + 1°C, T + 2°C and T + 3°C scenarios are obtained to be 10, 28 and 43%, respectively. Whereas, the average value of increase in total streamflow runoff for T + 1°C, T + 2°C and T + 3°C are obtained to be 7, 19 and 28%, respectively. Changes in rainfall by −10 and + 10% vary the average annual snowmelt runoff over the T + 2°C scenario by −1% and + 1% only. The result shows that melt is much more sensitive to increase in temperature than to rainfall.     

变化环境下嫩江富拉尔基站径流响应

以嫩江富拉尔基断面以上流域为研究区,分别采用统计方法和模型方法,评价土地利用变化和尼尔基水库运行对径流变化的影响,并分析两者综合影响下径流的变化趋势。结果表明:尼尔基建库前后流域土地利用变化不明显,而下游径流变化明显,水库对径流变化的影响更大;SWAT模型适用于研究区径流模拟,水库运行、土地利用变化对径流变化的影响分别占92.86%和7.14%;相同降水和水库运行条件下,1990—2020年土地利用变化具有使年径流量先减少后增加的效应,水库运行对径流的年内分配有显著影响。     

Reliability analysis for reservoir water supply due to uncertainties in hydrological factors,rainfall-runoff routing and operating rule curves

This study aims at developing a reliability-analysis model (RA_WS_RES) to quantify the effect of variations in uncertainties factors regarding the reservoir inflow and outflow at various 10-day periods on the reliability of water supply from the reservoir. The uncertainty factors considered are classified into three types: the hydrological factors (rainfall, baseflow, and initial water level of the reservoir), the reservoir operation rules for the water-allocation model (RIBASIM), and the parameters of rainfall-runoff model (i.e. Sacramento Soil Moisture Accounting, SAC-SMA). In the proposed RA_WS_RES model, the reliability of the water supply attributed to the uncertainty factors considered can be quantified by collaborating the multivariate Monte Carlo simulation (MMCS) methods and uncertainty-risk (advanced first order and second moment, AFOSM) analysis. Shihmen Reservoir watershed in Northern Taiwan is selected as the study area and four associated demand nodes are regarded as the study nodes; the hourly rainfall data from 1987 to 2014 and other hydrological data (i.e. rainfall, baseflow, and initial water level of the reservoir) as well as the operation rule curves are adopted in the model development and application. The results from the numerical experiences indicate that among the uncertainty factors concerned, the average rainfall depth at the current 10-day period and the range between the lower and critical levels are more sensitive to the estimation of water supply from Shihmen Reservoir. Additionally, the impact of variation in baseflow on the reliability of the water supply from Shihmen Reservoir should be taken into account, especially in the dry season. In addition to rainfall and baseflow, the initial water level should be an important source for the water supply, and its effect gradually reduces with the 10-day period. Furthermore, the reliability of water supply is obviously impacted by the uncertainty in the range between the lower and critical rule level, especially in the dry season, due to its range being adversely related with the water supply. Eventually, the proposed RA_WS_RES model can effectively and reasonably quantify the reliability of water supply attributed to variations in uncertainty factors at different 10-day period under the consideration of climate change.     

Simulation-optimization model of reservoir operation based on target storage curves

This paper proposes a new storage allocation rule based on target storage curves. Joint operating rules are also proposed to solve the operation problems of a multi-reservoir system with joint demands and water transfer-supply projects. The joint operating rules include a water diversion rule to determine the amount of diverted water in a period, a hedging rule based on an aggregated reservoir to determine the total release from the system, and a storage allocation rule to specify the release from each reservoir. A simulation-optimization model was established to optimize the key points of the water diversion curves, the hedging rule curves, and the target storage curves using the improved particle swarm optimization （IPSO） algorithm. The multi-reservoir water supply system located in Liaoning Province, China, including a water transfer-supply project, was employed as a case study to verify the effectiveness of the proposed join operating rules and target storage curves. The results indicate that the proposed operating rules are suitable for the complex system. The storage allocation rule based on target storage curves shows an improved performance with regard to system storage distribution.     

Analysis of the effect of climate change on the Nakdong river stream flow using indicators of hydrological alteration

This study models the effect of climate change on runoff in southeast Korea using the TANK conceptual rainfall-runoff model. The results are assessed using the indicators of hydrological alteration (IHA) developed by U.S. Nature Conservancy. Future climate time series are obtained by scaling historical series, provided by four global climate models (GCMs, IPCC, 2007) and three greenhouse gas (GHG) emissions scenarios (IPCC, 2000), to reflect a maximum increase of 3.6 °C in the average surface air temperature and 33% in the annual precipitation. To this end, the spatio-temporal change factor method is used, which considers changes in the future mean seasonal rainfall and potential evapotranspiration as well as the daily rainfall distribution. In this study, the variance range for precipitation is from +3.55% to +33.44% compared to the present for years between 2071 and 2100. The variance range for the daily mean temperature is estimated between +1.59 °C and +3.58 °C. Although the simulation results from different GCMs and GHG emissions scenarios indicate different responses of the flows to the climate change, the majority of modeling results show that there will be more runoff in southeast Korea in the future. According to the analysis results, the predicted impacts of hydrological alteration caused by climate change on the aquatic ecosystem are as follows: 1) an increase in the availability of aquatic ecosystem habitats in Nakdong River in future summers and winters, 2) an increase in stress on the aquatic ecosystem due to extremely high stream flow, 3) an increase in the stress duration of flood events for the Nakdong River downstream and 4) an increase in aquatic ecosystem stress caused by rapid increases or decreases in stream flow.     

Integrated Reservoir Management System for Adaptation to Climate Change: The Nakdong River Basin in Korea

This study begins with the premise that current reservoir management systems do not take into account the potential effects of climate change on optimal performance. This study suggests an approach in which multi-purpose reservoirs can adapt to climate change using optimal rule curves developed by an integrated water resources management system. The system has three modules: the Weather Generator model, the Hydrological Model, and the Differential Evolution Optimization Model. Two general circulation models (GCMs) are selected as examples of both dry and wet conditions to generate future climate scenarios. This study is using the Nakdong River basin in Korea as a case study, where water supply is provided from the reservoir system. Three different climate change conditions (historic, wet and dry) are investigated through the compilation of six 60 years long scenarios. The optimal rule curves for three multi-purpose reservoirs in the basin are developed for each scenario. The results indicate that although the rule curve for large-size reservoir is less sensitive to climate change, medium or small-size reservoirs are very sensitive to those changes. We further conclude that the large reservoir should be used to release more water, while small or medium-size reservoirs should store inflow to mitigate severe drought damages in the basin.     

Adaptive Reservoir Management by Reforming the Zone-based Hedging Rules against Multi-year Droughts

In this study, the zone-based hedging rule, which is the main operating policy adopted from multipurpose reservoirs in Korea is adjusted to reflect the multi-year droughts caused by climate change. Annual synthetic inflow series with different magnitudes of long memory were generated using the autoregressive fractional integrated moving average (ARFIMA) model. The generated inflow series were then disaggregated into 10-day series and utilized as input variables to derive the alternative hedging rules. The alternative hedging rules from this study were used in adaptive reservoir management by newly updated information. Finally, the performance of the suggested policy is measured in terms of frequency and magnitude under the historical inflow series. As a result, adaptive reservoir management demonstrated improvements in the following terms of the frequency of critical failures (water deficit ratio greater than 30%): 6.14% of the simulation period in the status quo (SQ) policy, and 2.99% in the adaptive management. However, the overall reliability of the reservoir during the simulation horizon was better when operated with the SQ policy (41.19%) than the results from adaptive management (26.42%). Because this result is in a good agreement with the original objective of the hedging rules, the adaptive policy suggested in this study holds promise and may be utilized in further reservoir management with an increase of potential drought risk from climate change.

     

Experimental Verification of the Effect of Slope and Land Use on SCS Runoff Curve Number

The present study investigates experimentally the effect of watershed (i.e. field plot of 22 m?×?5 m) slope on rainfall-generated runoff and, in turn, the runoff curve numbers (CN) resulting from field plots (with land use of maize and sugarcane on the soil falling in Hydrologic Soil Group C) located in Roorkee, (India). The results indicated that the plot of 5 % slope yielded the largest runoff and, in turn, CN compared to those due to the plots of 3 and 1 % grades, for the same rainfall, soil, and land use. The CN derived from the present study were quite close to the NEH-4 CN-values, indicating satisfactory match between the two. The use of slope adjusted CN-values in the standard CN method significantly (at 5 % level) improved the otherwise underestimated large runoff events, i.e. model efficiency E improved from 0.47 to 0.78, and R² from 0.71 to 0.83.     

下岸水库对永安溪水文情势的影响分析

为了定量评估永安溪下岸水库对下游水文情势的影响,利用永安溪柏枝岙水文站1980—2020年的径流序列,采用不均匀系数、完全调节系数和集中度分析水库运行前后永安溪径流年内分配变化,并利用RVA法评估水文整体改变度。结果表明:下岸水库的蓄丰补枯作用明显,径流年内分配趋于均匀化;在取得防洪效益的同时,水库的运行也对永安溪水文情势产生了中度改变,改变度达42.82%,对流域内水生生态系统的健康形成潜在影响。     

密云水库入库径流演变特性及成因分析

密云水库是北京唯一的地表饮用水源地,水库水量的多少直接关系到首都人民的生活。根据密云水库1960—2009年年入库径流量和汛期径流量2类序列,采用随机水文学方法结合序列统计性质揭示了入库径流演变规律,从降雨、人类活动和土地利用变化角度探讨入库径流演变的成因。结果表明:年入库径流和汛期入库径流都呈现减小趋势,1999年以后减小趋势更为明显,年径流减小程度比汛期显著,年际变化有明显的阶段性。受多种因素影响的密云水库入库径流序列包含相依成分,特别是年径流序列相依关系较强。入库径流减少的趋势不是单一由降水造成,流域内人类活动和土地利用变化是径流量锐减的主要原因。     

Integrated Reservoir Management System for Flood Risk Assessment Under Climate Change

Operations of existing reservoirs will be affected by climate change. Reservoir operating rules developed using historical information will not provide the optimal use of storage under changing hydrological conditions. In this paper, an integrated reservoir management system has been developed to adapt existing reservoir operations to changing climatic conditions. The reservoir management system integrates: (1) the K-Nearest Neighbor (K-NN) weather generator model; (2) the HEC-HMS hydrological model; and (3) the Differential Evolution (DE) optimization model. Six future weather scenarios are employed to verify the integrated reservoir management system using Upper Thames River basin in Canada as a case study. The results demonstrate that the integrated system provides optimal reservoir operation rule curves that reflect the hydrologic characteristics of future climate scenarios. Therefore, they may be useful for the development of reservoir climate change adaptation strategy.     

The effects of climate change on the water resources of the Geumho River Basin,Republic of Korea

Assessments of the variation and vulnerability of water resources due to climate change are essential for future planning in agriculture. In this study, the impacts and uncertainty associated with climate change on water resources in the Geumho River Basin were measured based on the relative change in the mean annual runoff and the aridity index. Statistically adjusted and downscaled multi-ensemble General Circulation Model (GCM) predicted rainfall and temperature data for three representative concentration pathways (RCPs) (RCP2.6, 4.5 and 8.5) were applied to two lumped parameter conceptual rainfall runoff models. The results revealed considerable uncertainty in the projected temperature, rainfall, potential evapotranspiration (PET), runoff and aridity index (AI). Additionally, temperature and rainfall were predicted to increase significantly in the future. The PET was projected to increase by a mean (range) of 9% (7–12%), 18% (9–30%) and 25% (8–49%), while the mean annual runoff was projected to change by a mean (range) of 1% (−33 to 40%), −9% (−47 to 27%) and −4% (−44 to 35%), in the 2030s, 2060s and 2090s, respectively. The AI was projected to decrease in the future, particularly for the RCP8.5. Overall, the results of this study indicate that climate change will most likely lead to lower water resource levels than are currently present in the Geumho River Basin.     

枫树坝水库洪水实时预报校正方法研究

枫树坝水库降雨径流概念性模型的建立及其自动采集系统的完善，为枫树坝水库洪水实时预报校正研究提供了前提条件。概念性水文模型考虑因素尽管样全面，但汇流经验单位线计算流量过程精度有待提高。基于洪水预报误差信息，对一价自回归模型自适应递推、二阶自回归自适应递推和卡尔曼滤波校正方法进行研究分析。实际洪水与模拟计算结果对比分析表明，二阶自加归递推和卡尔曼滤波校正计算方法提高了洪水预报精度。     

Optimizing Reservoir Operation Policy Using Chance Constraint Nonlinear Programming for Koga Irrigation Dam,Ethiopia

One of typical problems in water resources system modeling is derivation of optimal operating policy for reservoir to ensure water is used more efficiently. This paper introduces optimization analysis to determine monthly reservoir operating policies for five scenarios of predetermined cropping patterns for Koga irrigation scheme, Ethiopia. The objective function of the model was set to minimize the sum of squared deviation (SSD) from the desired targeted supply. Reservoir operation under different water availability and thresholds of irrigation demands has been analyzed by running a chance constraint nonlinear programming model based on uncertain inflow data. The model was optimized using Microsoft Excel Solver. The lowest SSD and vulnerability, and the highest volumetric reliability were gained at irrigation deficit thresholds of 20 % under scenario I, 30 % under scenario II, III and V, and at 40 % under scenario IV when compensation release is permitted for downstream environment. These thresholds of deficits could be reduced by 10 % for all scenarios if compensation release is not permitted. In conclusion the reservoir water is not sufficient enough to meet 100 % irrigation demand for design command areas of 7,000 ha. The developed model could be used for real time reservoir operation decision making for similar reservoir irrigation systems. In this specific case study system, attempt should be made to evaluate the technical performance of the scheme and introduce a regulated deficit irrigation application.     

基于随机森林与支持向量机的水库长期径流预报

水库长期径流预报对于研判水文情势变化和指导水库调度管理具有重要意义。针对云南龙江水库年、汛期和枯水期平均入库径流,利用随机森林从环流指数、海温、气压和前期月径流中选取关键预报因子,基于粒子群与交叉验证相结合的算法优选参数,建立随机森林与支持向量机模型,开展龙江水库入库径流预报研究。结果表明:太平洋中北部与西部气候因子对径流预报的影响较大,前期月径流对年、汛期径流的重要性偏低,但对枯水期的影响程度与部分气候因子相当。随机森林与支持向量机模型总体精度较高,模拟与预报的合格率均达到85%以上,平均绝对百分比误差均低于15%,支持向量机的泛化能力强于随机森林,但二者在局部极值流量处的预报精度尚有待提升。