Joint Design,Operation And Risk Control For Flood Limited Water Levels Of Multi-reservoir Systems

The reservoir operation is a key technical mean to realize the safe and efficient utilization of flood resources.However,the number of the reservoirs for coordinated flood control in the basin increases and the demand of flood resources management becomes more and more complex in the new period.It is urgent to develop systematic research on the joint flood control operation of the complex multi-reservoir systems,and the purpose of which is to make up for the lack of the traditional single-reservoir operation theory.Therefore,with the multi-reservoir system of the Hanjiang River Basin as a case study,this thesis focused on the joint design,operation and risk control of multi-reservoir systems from three aspects: the joint design of multi-reservoir system flood storages,the multi-reservoir system flood storage allocation rules,and the dynamic control of multi-reservoir flood limited water levels.The main contents and results were summarized as follows:(1)A flood damage assessment index based on conditional value-at-risk(CVa R)was constructed for joint design of multi-reservoir system flood storage values(or flood limited water levels,FLWLs).First,the concept of CVa R in economic fields was incorporated in quantifying the flood damage loss for a single-reservoir system,and its expression under the non-stationary condition is deduced.Then,the CVa R in the application of the adaptive reservoir FLWL optimal model in a changing environment was taken as an example to verify the proposed flood damage loss evaluation index.Finally,the CVa R was extended from a single-reservoir system to a complex multireservoir system,and it was used to derive the joint optimal design of multi-reservoir system flood storage values.Results show that: the CVa R not only can represent the possible flood damage loss over a time horizon in the future,but also can reflect the flood risk probability by the confidence level;there is a feasibility interval solution for the joint optimal design of multi-reservoir system flood storage values if the constraint of the CVa R value was satisfied,and the boundary of this feasibility interval was determined by the minimum flood storage value of each reservoir in the multi-reservoir system.(2)A flood storage allocation rule which can maximize the benefit of hydropower generation was theoretically derived for a multi-reservoir system.First,an energy equation,the E-function,was derived to describe the relationship between the hydropower generation and the change in the reservoir flood storage.Then,the Efunction of a multi-reservoir system,which was deduced on the basis of energy equation in a single-reservoir system,can be represented as a function of two variables: the proportional coefficient(γ,which represents the proportional relationship between the two reservoirs in a two-reservoir system)and the total change in flood storage.Finally,a proportionality coefficient discrimination(i.e.,the flood storage allocation rule)was summarized to guide the optimal allocation of flood storage values in multi-reservoir systems.Results show that: the E-function can be used to directly estimate the total hydropower generation for multi-reservoir systems within acceptable error when compared with the results of numerical hydropower simulation;the optimal reservoir flood storage allocation scheme for a two-reservoir system can be explicitly obtained by using the proportionality coefficient discriminant.(3)A two-stage flood risk analysis method(TSFRAM)was proposed to establish a real-time operation model for the dynamic control of multi-reservoir flood limited water levels during flood seasons.First,the TSFRAM evaluated the uncertainty of the flood forecasting by dividing the operation horizon into the forecast lead-time and the beyond-forecast time period.The risk within the forecast lead-time induced by the streamflow uncertainty was estimated by counting the frequency of failure numbers among all scenarios with the help of the scenario-based forecasts.The risk beyond the forecast time period caused by the possible high water level at the end of the forecast period was determined using reservoir flood routing with the design flood hydrographs.The proposed TSFRAM was then verified using stochastic simulations method based on Monte Carlo sampling.Finally,a real-time flood control operation model for the multi-reservoir system was established by taking the TSFRAM as a constraint,and the objective of this model was to maximize the hydropower benefit,which can realize the dynamic control of the FLWLs in multi-reservoir systems.Results show that: the proposed TSFRAM can both consider the risk within the forecast and the risk beyond the forecast time period;the proposed real-time flood control operation model can increase the total hydropower benefit without increasing the flood risk(e.g,the hydropower generation in summer flood season for the five-reservoir system of the Hanjiang River Basin can increase by 0.23 billion k Wh in 2010 year).