Study On Long-term Hydrological Forecast And Its Application In Plain Flood Resource Utilization

Medium and long-term hydrological forecasting plays an important role ranging from reservoir operation, flood control yield to disaster mitigation, floodwater resource utilization, water right management, etc. Medium and long-term hydrological forecasting has been researched by many hydrology scientists. With the new techniques of computer and mathematics methods coming out, medium and long-term hydrological forecasting has a fast development. But it is still under development and lagged behind production process compared to short-term forecast because of its complexity and short of hydrologic data. More attention has been paid to statistical properties in hydrological series in the prediction theory study, and less in physics causes analysis. Neglecting the validity of forecasting methods makes the existing methods not effectively popularized and applied, and used only as a reference in macro-control of water resource in practical application. For these reasons, this paper studied on methods of long-term hydrological forecasting based on physics factor analysis and its application in plain flood resource utilization. The main contents and results are as follows:(1) Physical factors of regional hydrologic influence are analyzed from the mechanism of hydrological cycle, including astronomical factors, sea surface temperature, atmospheric circulation factors, and so on. Sunspot activity, relations among sun, moon and earth, changes of North Pacific sea surface temperature, ENSO events, atmospheric circulation factors which affect regional hydrological situation are analyzed in this paper. It gives a theoretical support for the study of medium and long-term hydrological forecasting based on physical factors analysis.(2) The relationship between the meteorological factors and the flood hazards has been established, considering that the existing forecasting methods can not express the possibility and degree of flood. Three methods for forecasting the trends of floods and droughts are proposed, and the mathematical formulae are derived through the combination of the meteorological and stochastic concepts and methods. These three methods are the shift probability, the phase of the Sun activities, El Nino events. These methods have been used to forecast the future trends of floods and droughts in Northeast China, which have been proved to be a new way to the study of flood hazard time domain characteristics and an effective reference for guiding regional flood utilization and the practical flood risk management. (3) Association rules mining is introduced to medium and long-term hydrological forecasting, aiming on the variety and complex relationships of long-term hydrological forecasting data and difficulty search and management for forecasting. The model of long-term hydrological forecasting based on association rules mining is established in this paper. Firstly, forecast factors are selected to constitute the long-term forecast database based on the forecast object considering the characteristics of hydrology forecast. Secondly, the forecast database is established based on data cleaning and pretreatment. Finally, the strong association rules which accord with the min-support and min-confidence are extracted by the method of apriori. Long-term hydrological forecasting model is established based on the strong association rules. A case is studied to validate this new model, and the results reveal that the model can reduce workload and is helpful to finding the interesting strong association rules for the goal of forecasting from massive data.(4) Long-term qualitative and quantitative synthesis prediction model has been established based on the variable topological structure of artificial neural network in this paper, because that the quantitative forecasting method has large errors and the qualitative forecasting methods can not satisfy the production process, Firstly, the qualitative forecasting model is established based on physical factors analysis. Secondly, the quantitative forecasting model is established based on changing output node. Finally, conclusions are drawn by combining qualitative and quantitative forecasting results. Two cases are used to validate this new method, and the results reveal that the method is a better way to improve forecasting accuracy and stability than either of the models used separately.(5) There are different kinds of future information uncertainty in the flood resource utilization. They are the main resources of risk. The future state about all kinds of input information in the system can be defined in different degree by using the results of medium and long-term hydrological prediction. The paper analyzes the application of long-term runoff forecast in plain flood resource utilization. Therefore, the risk and the loss during the process of flood utilization can be avoided or reduced. The preplan of flood utilization can be made and the risk and the loss during the process of flood utilization can be avoided or reduced as more as possible based on the results of medium-term runoff forecasting. The application examples of 2005 and 2006 show that the higher precision of long-term hydrological forecast play a positive effort in making and actualizing flood resource utilization preplan. The risk and the loss during the process of flood utilization has been avoided and decreased to the greatest extent and the flood utilization has achieved the biggest benefit by applying the medium and long-term hydrological prediction.Finally, conclusions are made, and problems for further study are reviewed.