Flood Limited Water Level Research Articles

Floodwater Utilization Based on Reservoir Pre-Release Strategy Considering the Worst-Case Scenario

Utilizing floodwater resources is important in relieving water shortages, and dynamic control of the flood limited water level (FLWL) for reservoir operation in a flood season is an effective method to achieve this objective. Based on the capacity-constrained pre-release method, this study proposed an improved dynamic control method that considered the duration of dry periods and the lead time of flood forecasts. The pre-release process was divided into two periods: water use and flood control. Taking Xianghongdian Reservoir in the Huai River Basin of China as an example, this study analyzed the statistical laws of continuous dry periods and effective flood forecast lead times and compared the effects of the negative exponential and asymptotic regression models in fitting the dry period distribution. We also calculated the floodwater volume over the FLWL in different situations and evaluated the flood control risks in a worst-case scenario. Statistical law of the dry period duration showed obvious negative index distribution characteristics; the relationship between increased water storage, dry period, and lead time can provide support for the operation decisions of the reservoir. The method did not increase the flood control risk under worst-case scenarios, and it can be used to effectively utilize reservoir floodwater resources.

Quantitative assessment of adaptive measures on optimal water resources allocation by using reliability, resilience, vulnerability indicators

Water resources allocation is facing great challenge, since hydrological series have shown non-stationarity with high uncertainty due to climate change and human activities. Adaptive measures are suggested to respond to the challenge. Aiming at quantitatively assess the impact of adaptive measures on optimal water resources allocation, we proposed a framework based on reliability, resilience and vulnerability indicators. Two representative concentration pathway (RCP) scenarios (RCP2.6 and RCP4.5) of one global climate model were used to project future climate, and the variable infiltration capacity hydrological model was used to simulate streamflow. Three adaptive measures [water saving measure, water transfer project, dynamic control of flood limiting water levels (FLWLs) for reservoir operation] were combined to eight scenarios, then scenarios were applied to the allocation model to get different optimal allocation schemes which were assessed by RRV indicators. The results show that water saving measure decreases the vulnerability by 79 × 106 m3, water transfer project decreases the resilience by 17% in every scenario and dynamic control of FLWLs increases the reliability by 23.53% to the greatest scale. But the impacts of latter two adaptive measures are restricted to the areas which are geographically close to water supply projects. The uneven spatial distribution and decrease of streamflow will increase the risk of water shortage in the future. Optimal water allocation can reduce this risk and make 23 of 28 operational zones stable. Water saving measure is significantly valid in the rest 5 operational zones, but its impact is not positive to all water use sectors. Overall, our study helps understanding the interaction between adaptive measures and water resources system, and making guidelines for effective adaptation planning.

Multi-Objective Optimal Scheduling Model of Dynamic Control of Flood Limit Water Level for Cascade Reservoirs

Reservoirs play a significant role in water resources management and water resource allocation. Traditional flood limited water level (FLWL) of reservoirs is set as a fixed value which over-considers the reservoir flood control and limits the benefits of reservoirs to a certain extent. However, the dynamic control of the reservoir FLWL is an effective solution. It is a method to temporarily increase the water level of the reservoir during the flood season by using forecast information and discharge capacity, and it can both consider flood control and power generation during the flood season. Therefore, this paper focuses on multi-objective optimal scheduling of dynamic control of FLWL for cascade reservoirs based on multi-objective evolutionary algorithm to get the trade-off between flood control and power generation. A multi-objective optimal scheduling model of dynamic control of FLWL for cascade reservoirs which contains a new dynamic control method is developed, and the proposed model consists of an initialization module, a dynamic control programming module and an optimal scheduling module. In order to verify the effectiveness of the model, a cascade reservoir consisting of seven reservoirs in the Hanjiang Basin of China were selected as a case study. Twenty-four-hour runoff data series for three typical hydrological years were used in this model. At the same time, two extreme schemes were chosen for comparison from optimized scheduling schemes. The comparison result showed that the power generation can be increased by 9.17 × 108 kW·h (6.39%) at most, compared to the original design scheduling scheme, while the extreme risk rate also increased from 0.1% to 0.268%. In summary, experimental results show that the multi-objective optimal scheduling model established in this study can provide decision makers with a set of alternative feasible optimized scheduling schemes by considering the two objectives of maximizing power generation and minimizing extreme risk rate.

Risks Analysis of Discarding Water in Power Generation Process of Hydropower Station

Hydropower, as a kind of clean energy, has the characteristics of rapid response to load changes, and is often used to undertake peak regulation and frequency regulation tasks. However, due to the uncertainties of reservoir inflow and runoff, the relative lag of power grid outgoing channels, and the interconnection of intermittent new energy, such as wind power and solar energy, the hydropower system is facing enormous peak regulation pressure and the continuous prominent problem of discarding water. In the study, aiming at the problem of risk control of discarding water in power generation process of hydropower station, a practical calculation method of risk of discarding water in power generation is proposed based on the analysis of frequency of runoff. Taking the Ertan hydropower station as an example, the corresponding water level processes of different discarding water risks under the control of pre-flood falling water level, flood limit water level and storage water level after flood season are deduced, and in the routine dispatching process, the water level operation control guidance corresponding to different discarding risk is introduced. The simulation results show that the proposed discarding water risk control method is practical and effective, and can provide guidance for discarding water risk control in the actual dispatching process of hydropower station.

A general framework of design flood estimation for cascade reservoirs in operation period

The hydrological regimes of downstream reservoirs have been significantly altered due to the operation and regulation of upstream cascade reservoirs. The original design flood quantiles, namely “design flood in construction period”, do not consider anthropogenic impacts in reservoir operation period, and have led to enormous conflicts between flood control and conservation. In this study, the “design flood and flood limited water level in operation period” are defined for practical application. We establish a general framework to measure the spatiotemporal pattern of streamflow and to estimate design floods of cascade reservoirs in operation period. The multivariate t-copula and a genetic algorithm strategy are proposed to solve the curse of dimensionality encountered in the derivation of most likely regional composition. The Jinsha River and Yalong River cascade reservoir system in China, which consists of 13 large reservoirs with the total storage capacity of 74.06 billion m3 and hydropower capacity of 71.47 GW, is selected as a case study. Results indicate that: (1) The curse of dimensionality can be well addressed by applying multivariate t-copula to build high dimensional joint distribution and using the genetic algorithm to achieve the most likely regional composition. (2) Compared with the design floods in construction period, the design floods of downstream reservoirs in operation period have been significantly reduced due to the upstream reservoir regulation. The 1000-year design peak flood discharge, 3-day, 7-day and 30-day flood volumes of Xiangjiaba reservoir decrease by 38.7%, 37.4%, 34.2% and 13.8%, respectively. (3) The flood limited water level of these reservoirs can be raised without increasing flood control risks in operation period. The cascade reservoirs in the Jinsha River and Yalong River can generate 3.28 billion kW h more hydropower (or increase 4.3%) annually during flood season.

Determination of drought limit water level of importing reservoir in inter-basin water transfer project under changing environment

Drought occurrence and its related impacts are a major concern in many basins throughout the world. Reservoirs play a very important role in drought resistance. Compared with the reservoir flood limit water level, the drought limit water level belongs to a new concept. This paper took the Yuqiao reservoir as the study area and proposed a new method to determine the drought limit water level under changing environment. Firstly, the Mann-Kendall (M-K) method and cluster analysis method were employed to test the trend and change point of the series based on the runoff series of Yuqiao reservoir. On this basis, the runoff frequency curve and design runoff process under current condition were obtained by Pearson-III frequency analysis. Secondly, copula function was used to analyze the synchronous-asynchronous encounter probability of rich-poor runoff of Yuqiao reservoir and Panjiakou reservoir. The available transferred volume of Yuqiao reservoir in dry year was analyzed. Finally, according to the runoff and available transferred volume, the total inflow of Yuqiao reservoir in dry season was calculated. Combining water demand and total inflow of Yuqiao reservoir, the drought limit water level was calculated by month to month. The study results can provide necessary technique support for reservoir drought emergency management.

Rainfall and runoff characteristics in a karstic basin of China

AbstractThis paper examines the rainfall and runoff characteristics in a karstic basin of China. The results indicated that the inner-annual distributions of rainfall and runoff were uneven and slightly different, as the concentration period of rainfall (from April to October) was earlier; there was a delay of about a month before the runoff (from May to September), and the concentrated volume accounted for 87% of annual precipitation or annual streamflow. Interannually, rainfall changed more significantly than runoff, the wet years lasted longer than the dry years (rainfall), while the high and low flow years were equal for runoff. In addition, judging from the value of the Mann-Kendall test, the average annual change of rainfall (−2.36) was more significant than that of runoff (−2.05), and the seasonal pattern of runoff maintained an opposite tendency in autumn and winter before 1990. The changes in runoff were mainly associated with rainfall and the formation conditions in the karstic area, and the reservoir in this basin should be operated with different flood limiting water levels, and the vegetation coverage should be improved.

The Application of a Multi-Beam Echo-Sounder in the Analysis of the Sedimentation Situation of a Large Reservoir after an Earthquake

The Wenchuan Earthquake took place in the upper reach catchment of the Min River. It resulted in large amounts of loose materials gathering in the river channel, leading to changes in the sediment transport system in this area. The Zipingpu Reservoir is the last and the largest reservoir located in the upper reach of the Min River. It is near the epicenter and receives sediment from upstream. This paper puts forward a study on the reservoir sedimentation and storage capacity of the Zipingpu Reservoir, employing a multi-beam echo-sounder system in December 2012. Then, the data were merged with digital line graphics and shuttle radar topography mission data in ArcGIS to build a digital elevation model and triangulate the irregular network of Zipingpu Reservoir. Via the analysis of the bathymetric data, the results show the following: (1) The main channels of the reservoir gradually aggrade to a flat bottom from the deep-cutting valley. Sedimentation forms a reach with a W-shaped longitudinal thalweg profile and an almost zero slope reach in the upstream section of the reservoir due to the natural barrier induced by a landslide; (2) The loss ratios of the wetted cross-section surface are higher than 10% in the upstream section of the reservoir and higher than 40% in the natural barrier area; (3) Comparing the surveyed area storage capacity of December 2012 with March 2008, the Zipingpu Reservoir has lost 15.28% of its capacity at the dead storage water level and 10.49% of its capacity at the flood limit water level.

Reservoir operation by staging due to climate variability

ABSTRACTThe changing environment enhances the hydrological cycle and increases the frequency of extreme floods. In this paper, the impacts of climate variability on flood season segmentation are determined and the scientific basis for determining corresponding flood limiting water levels (FLWLs) is provided. Climate variation was determined and then the flood season was divided into several sub-seasons using the results of the set pair analysis method (SPAM) and four indices; peak floods crossing the transitional periods were sampled to obtain a design flood hydrograph; and, finally, seasonal FLWLs were determined for reservoir operation. The performance of this reservoir staging operation was evaluated for a case study in the Chengbihe Reservoir, China.

Conditional Value-at-Risk for Nonstationary Streamflow and Its Application for Derivation of the Adaptive Reservoir Flood Limited Water Level

AbstractThe existing risk-based approaches for quantifying expected flood damage loss may not be suitable in the changing environment when streamflow becomes nonstationary. Conditional value-at-ris...

The Application and Research of Dynamic Control the Flood Limited Water Level of Wuqiangxi Reservoir

This paper briefly introduces the method, content and approval process of the dynamic control of the flood limited level in Wuqiangxi reservoir, and summarizes the benefits since the implementation of dynamic control. The relevant research results of this paper can be used as reference for production technology management personnel.

Assessing the effects of adaptation measures on optimal water resources allocation under varied water availability conditions

Human activities and climate change have altered the spatial and temporal distribution of water availability which is a principal prerequisite for allocation of different water resources. In order to quantify the impacts of climate change and human activities on water availability and optimal allocation of water resources, hydrological models and optimal water resource allocation models should be integrated. Given that increasing human water demand and varying water availability conditions necessitate adaptation measures, we propose a framework to assess the effects of these measures on optimal allocation of water resources. The proposed model and framework were applied to a case study of the middle and lower reaches of the Hanjiang River Basin in China. Two representative concentration pathway (RCP) scenarios (RCP2.6 and RCP4.5) were employed to project future climate, and the Variable Infiltration Capacity (VIC) hydrological model was used to simulate the variability of flows under historical (1956–2011) and future (2012–2099) conditions. The water availability determined by simulating flow with the VIC hydrological model was used to establish the optimal water resources allocation model. The allocation results were derived under an extremely dry year (with an annual average water flow frequency of 95%), a very dry year (with an annual average water flow frequency of 90%), a dry year (with an annual average water flow frequency of 75%), and a normal year (with an annual average water flow frequency of 50%) during historical and future periods. The results show that the total available water resources in the study area and the inflow of the Danjiangkou Reservoir will increase in the future. However, the uneven distribution of water availability will cause water shortage problems, especially in the boundary areas. The effects of adaptation measures, including water saving, and dynamic control of flood limiting water levels (FLWLs) for reservoir operation, were assessed and implemented to alleviate water shortages. The negative impacts from the South-to-North Water Transfer Project (Middle Route) in the mid-lower reaches of the Hanjiang River Basin can be avoided through the dynamic control of FLWLs in Danjiangkou Reservoir, under the historical and future RCP2.6 and RCP4.5 scenarios. However, the effects of adaptation measures are limited due to their own constraints, such as the characteristics of the reservoirs influencing the FLWLs. The utilization of storm water appears necessary to meet future water demand. Overall, the results indicate that the framework for assessing the effects of adaptation measures on water resources allocation might aid water resources management, not only in the study area but also in other places where water availability conditions vary due to climate change and human activities.

Methodology that improves water utilization and hydropower generation without increasing flood risk in mega cascade reservoirs

The optimal dynamic operating flood limiting water levels (FLWLs) of cascade reservoirs are the critical driver for satisfactorily compromise flood control and hydropower needs. We proposed an adept multi-objective dynamic operating FLWLs methodology based on an evolutionary algorithm with a modified aggregation-decomposition method for optimal operation of three cascade reservoirs. The modified aggregation-decomposition method is used to identify the upper boundary of FLWLs of cascade reservoirs by extending the flood routing process for multiple time-delay inflows - single outflow patterns. The non-dominated sorting genetic algorithm-II (NSGA-II) was then used to efficiently counterbalance the risks of flood control and hydropower generation in the dynamic operation of cascade reservoirs. Three mega cascade reservoirs in the Yangtze River basin of China are selected as a case study. The optimal solutions of cascade reservoirs operation are compared with those of single reservoir operation. The results indicate (1) the minimum power generation risk solution could largely improve the water utilization and hydropower generation by 5.43% and 6.48% (3.71billion kW·h/year), respectively, as well as mitigate the power generation risk by 5.8% with a small cost of increasing flood risk by 0.3%; and (2) the minimum flood control risk solution could reduce the flood risk and power generation risk by 0.4% and 0.7%, respectively, and enhance the water utilization and hydropower generation by 0.64% and 2.18%, respectively. We demonstrate the proposed methodology could largely improve the water utilization and hydropower generation without increasing flood risk. Moreover the widespread Pareto front solutions allow decision-makers to determine the best compromising solution with counterbalanced risks of flood control and hydropower generation. The hydropower generation indeed would provide extensive economic benefits and contribute to growth in social well-being with low environmental impact. Thus, the proposed methodology can be used as a basis of analysis for a large number of constructed and under-constructed mega dams in upper Yangtze river to overcome the bottleneck of new energy development and water resources sustainability management.

Adaptive reservoir flood limited water level for a changing environment

As streamflow is non-stationary due to climate change and human activities, adapting reservoir operation in the changing environment is of significant importance. Specifically, the flood limited water level (FLWL) needs to be re-established to ensure flood safety when the reservoir inflow is altered. The aims of this study are: (1) to clarify the relationship between the FLWL and streamflow when statistical parameters of the flood peak and volume vary through time and (2) to re-establish the FLWL when the reservoir inflow changes under the non-stationary condition. The adaptive FLWL is derived based on flood routing of non-stationary design floods, and the flood risk probability is then estimated. With China’s Three Gorges Reservoir (TGR) as a case study, the changing pattern of FLWL is quantified when statistical parameters (i.e., mean, $$ C_{\text{V}} $$ and $$ C_{\text{S}} $$ ) of design floods have a linear temporal trend. The results indicate that the FLWL is sensitive with design floods, i.e., (1) means of design flood peak, 3-day volume, 7-day volume, 15-day volume and 30-day volume yearly decrease by 33 m3/s, 0.008, 0.021, 0.482 and 0.905 billion m3, respectively, (2) when the non-stationary design flood is used, the cumulative flood risk probability of the reservoir water level exceeding 175.0 m during 2011–2030 decreases from 1.98 to 1.82% with the conventional FLWL scheme and (3) the FLWL of the TGR could be re-set without increasing the flood risk probability, and the FLWL would increase about 4.7 m by 2030 in this non-stationary streamflow scenario. These findings are helpful to derive the FLWL in a changing environment.

A method for implementing the real-time dynamic control of flood-limited water level

Many studies have proven that the dynamic control of flood-limited water level (DC-FLWL) is an effective methodology to balance flood control and water conservation for reservoir operations during the flood season. However, these studies have focused on determining the bound of FLWL; few studies have investigated the implementation of real-time DC-FLWL, which actually is the core of DC-FLWL. To implement real-time DC-FLWL, a new method for considering rain forecast is presented in the present study. The proposed method includes two procedures: prerelease and prefill, which constitute the prerelease–refill and the prefill–prerelease schemes. For each scheme, the categorical rain forecast with a lead time of 24 h is used as the trigger for different actions, while hydrological forecast and discharge are used to calculate the action details, including the water level reserved and the amount of discharge water. The method is examined via the operation of the flood event “19960810,” which occurred in the catchment of the Biliuhe reservoir in China. The results show that although the maximum water level and the maximum discharge of the three schemes have the same value, the water level at the end of both the prerelease–refill and the prefill–prerelease schemes of DC-FLWL is 68.8 and 68.5 m, which are both higher than the planning scheme, i.e., 68.1 m. These findings further confirm the effectiveness of DC-FLWL and also prove that the proposed method is suitable for implementing real-time DC-FLWL.

An Improved “Dynamic Control Operation Module” for Cascade Reservoirs

Reservoirs are one of the most efficient projects for water resources management, and also play an important role in flood control and conservation. Dynamic control of the reservoir flood limited water level (FLWL) is considered as an effective factor to ensure safety of the flood control during the flood season. The maximum allowed water level of cascade reservoirs is also a fundamental key element for implementing reservoir water level dynamic control operation. In this paper, we discussed and improved “Dynamic Control Operation Module for Cascade Reservoirs” (DCOMR). Therefore, a set of new formulas and new methodologies were proposed (NDCOMR) which considers intermediate variables forecast information, the release of the upstream reservoir and interval flow forecast information in effective lead times, which is applied to the dynamic operation of the maximum allowed water level of cascade reservoirs. The Bikou and Miaojiaba cascade reservoirs were selected as a case study. Based on numerical experiment results, the maximum allowed water level of cascade reservoirs at current time determined by NDCOMR was much safer than that determined by DCOMR. The NDCOMR is more rational and safer than DCOMR for flood control, without the need of reducing flood control standard.

Optimal Design of Seasonal Flood Limited Water Levels by Jointing Operation of the Reservoir and Floodplains

Reservoirs play an important role in the exploitation and utilization of water resources, and the flood limited water level (FLWL) is a key parameter to balance flood control and conservation in reservoir operation. This study is aimed at joint operation of the reservoir and floodplains to improve floodwater utilization and enhance economic benefits. The net profits, namely the benefits from power generation and water supply minus the losses from the flood volume diverted to floodplains, are set as the objective function. To maximize the net profits, an optimization model is then proposed. Finally, a nonlinear optimization technique, the complex method, is used to find the optimal seasonal FLWL. The China’s Danjiangkou Reservoir (DR) is selected as a case study. The results show that the joint use of floodplains enables 2.0 m and 0.5 m increment of FLWLs in summer and autumn, respectively, compared to the conventional FLWLs. Since the increment of the FLWL decreases the reservoir flood storage by 0.44 billion m3, the flood volume need to be diverted to floodplains is increased by 0.54 billion m3 per year. Meanwhile, the power generation and water diversion are increased by 0.59% and 2.99%, respectively. The assurance probabilities of power generation, water diversion and minimum flow are also increased by 1.1%, 0.96% and 0.70%, respectively. As a result, the economic benefits can be increased by 0.037 billion USD per year. It is concluded that the reservoir seasonal FLWL can be improved by joint operation of reservoirs and floodplains, which is able to enhance economic benefits without increasing flood risks. Moreover, the increment of economic benefits could be shared by reservoir managers and residents that live in floodplains. This novel operating approach is helpful to the integrated water resources management.

Adaptation of Cascade Hydropower Station Scheduling on A Headwater Stream of the Yangtze River under Changing Climate Conditions

Cascade hydropower stations are effective in water resource utilization, regional water allocation, and flood risk management. Under changing climate conditions, water resources would experience complex temporal and spatial changes, which may lead to various issues relating to flood control and water resource management, and challenge the existing optimal scheduling of cascade hydropower stations. It is thus important to conduct a study on cascade hydropower station scheduling under changing climate conditions. In this study, the Jinsha River rainfall–discharge statistical model is developed based on the statistical relationship between meteorological and runoff indicators. Validation results indicate that the developed model is capable of generating satisfactory simulation results and thus can be used for future Jinsha River runoff projection under climate change. Meanwhile, the Providing Regional Climates for Impacts Studies (PRECIS) is run to project future rainfall in the Jinsha River basin under two General Circulation Models (ECHAM5 and HadAM3P), two scenarios (A1B and B2), and four periods (1961–1990, 1991–2020, 2021–2050, and 2051–2099). The regional climate modeling data are analyzed and then fed into the Jinsha hydrological model to analyze the trends of future discharge at Xiangjiaba Hydro Station. Adaptive scheduling strategies for cascade hydropower stations are discussed based on the future inflow trend analysis and current flood scheduling mode. It is suggested that cascade hydropower stations could be operated at flood limited water level (FLWL) during 2021–2099. In addition, the impoundment of cascade hydropower stations should be properly delayed during the post-flood season in response to the possible occurrence of increased and extended inflow in wet seasons.

The Dynamic Control Bound of Flood Limited Water Level Considering Capacity Compensation Regulation and Flood Spatial Pattern Uncertainty

The dynamic control bound of flood limited water level (FLWL) is a fundamental and key element for implementing reservoir FLWL dynamic control. Due to the uncertainty of the inflow and the dimensional increase of the reservoirs, the calculation of the dynamic control bound of FLWL becomes more and more complicated. A new model that considers capacity compensation regulation and the uncertainty of flood spatial pattern (FSP) for a serial multipurpose reservoir system is developed to calculate the dynamic control bound of FLWL. This model consists of three modules: a compensation regulation module to analyze the feasibility to raise the FLWL and calculate the probable maximum upper bound of the FLWL, a risk control module containing a risk constraint to control flood risk and a Copula function to describe the uncertainty of the FSP, and a simulation operation module to simulate the flood control operation for cascade reservoirs. The proposed model was applied to Pankou-Huanglongtan cascade reservoirs in Du River basin. The application results showed that: 1) the proposed model could give a sufficient consideration about the uncertainty of the FSP, thus a safe and reasonable dynamic control bound of FLWL was derived. 2) the upper FLWL of Huanglongtan reservoir could rise up to 247.64 m from 247.00 m without increasing flood control risk and Huanglongtan reservoir could generate 9 and 7 billion kW.h extra hydropower energy during flood season in wet year 2000 and in dry year 1994, respectively.

Credibility theory based dynamic control bound optimization for reservoir flood limited water level

Summary The dynamic control operation of reservoir flood limited water level (FLWL) can solve the contradictions between reservoir flood control and beneficial operation well, and it is an important measure to make sure the security of flood control and realize the flood utilization. The dynamic control bound of FLWL is a fundamental key element for implementing reservoir dynamic control operation. In order to optimize the dynamic control bound of FLWL by considering flood forecasting error, this paper took the forecasting error as a fuzzy variable, and described it with the emerging credibility theory in recent years. By combining the flood forecasting error quantitative model, a credibility-based fuzzy chance constrained model used to optimize the dynamic control bound was proposed in this paper, and fuzzy simulation technology was used to solve the model. The FENGTAN reservoir in China was selected as a case study, and the results show that, compared with the original operation water level, the initial operation water level (IOWL) of FENGTAN reservoir can be raised 4 m, 2 m and 5.5 m respectively in the three division stages of flood season, and without increasing flood control risk. In addition, the rationality and feasibility of the proposed forecasting error quantitative model and credibility-based dynamic control bound optimization model are verified by the calculation results of extreme risk theory.