| Water resources assessment is the precondition of water resources planning, developing and utilization. The results of the first water resources assessment in China have been playing impartment role to economical construction. Because of the affection of more and more human activities and the climate changing, water resources condition in China has changed greatly. So the water resources assessment must be farther studied. On the base of the theory and mothed of sustainable development, for supplementing water resources assessment theory, it is important science significance and practicality value that studying the assessment theory, method and application to the surface water resources when the environment has changed.Following farther understanding about water resources, many results have been achieved. In the water resources assessment, many conditions are considered, from considering water quantity and quality respectively to combining the water quantity and quality, from analyzing the coherence runoff sequence to studying the nonconforming runoff sequence, from considering river accepting contamination capability solely to confirm ecological water requirements to considering to preserve ecological functions of the rive ecosystem keeping healthiness to confirm ecological water requirements. These results show water resources assessment is a task requiring innovation continuously.Studying the theory and method about water resources assessment has far-reaching theory significance and far-ranging society value.On a certain extent, the present water resource assessment method can't analyze the influence of environment changing to water resources and many entironment problems coming forth during the water resources utilization. In this paper, some problems existing in water resources assessment are specially studied taking the second nationwide water resources assessment in China.Firstly, the problem, of reverting calculation to water resources quantity under mutative conditions, is studied.Because of the affection of human activities and the climate changing, the total hydrological series may shade or mutate. These changing styles can't meet the requirement of water resources evaluation. So reverting calculation must be taken to the destroyed hydrological series. Now some existing methods have some bugs themselves, and then the reverting calculation results are disbelieved. So it is essential to study the revertingcalculation methods. In this paper, on the base of essential hydrological theory, rainfall is the main fact to influence the runoff, and rainfall only is influenced by climate change, notthe human activities. So the conventional method------rainfall-runoff correlativity methodis introduced. In the conventional method, the relationship between rainfalls of different rainfall stations and runoff is considered as linear. In fact, the relationship is nonlinear. Now the linear relationship is always used to replace the nonlinear relationship. Projection pursuit, a method to solve the nonlinear problems, is introduced to treat with the nonlinear relationship between multi-rainfall and runoff. And then, this method is used to the Heihe River. Reverting calculation is operated to the runoff of the Zhengyixia station. According to the calculation result, by this method, the calculated hydrological series have obvious coherence. Using this method, much time can be saved.Secondly, the problems of water resources evaluation on the base of water function areas compartmentalization and water resources available quantity calculation, on the base of water function region compartmentalization, are studied.Another aim of water resources evaluation is to answer the question of how much water is available in the river. And this is the base of water resource development. In this paper, according to the water quantity and water quality control equation, by the station totake water, the calculation methods of available water resources------reach head-controllingmethod and reach tail-controlling method are introduced. During calculation, the contamination quantity, which can be gained by investigating difficultly, can be identified, and the identifying method is introduced.Finally, the problem is how to confirm ecological water requirements.For the entironment problems increasing and entironment deteriorating increasingly, studying about ecological water requirements is lucubrated. Now the methods to confirm the ecological water requirements are on the base of conserving the ecosystem functions, and the arm is to maintain the ecosystem functions keeping healthiness. These methods have been playing important roles to keep the ecosystem healthiness. These methods can't embodiment the lost value as a result of water resources utilization. The harmony development of ecosystem and economical system is not studied commendably by combining the ecosystem and economical system. In this paper, ecological water requirements are considered by ecological value, and the ecosystem and economical system are combined to supply base data for calculating the water resources available quantity.This paper is composed of five chapters.Chapter 1: SummarizationFirstly the signification to select this subject is introduced. And then current waterresources menstruation and evaluation are summarized. The main methods, during water quality evaluation, are introduced and their characteristics are analyzed. The water resources evaluation in our country is summarized, and some problems are indicated. Arming at these problems, the studying emphases of this paper are introduced. Furthermore, the concept of the available water, studying status about the available water, influencing factors to the available water and principles which shoud be followed during calculating the available water are summarized. The studying methods how to calculate the available water are introduced.Chapter 2: Study of evaluating method to the surface water resources quantity when the environment has changed.Human change the runoff in river by taking water from river. At the same time, the changed layer changes conflux process. Before the hydrological serials is used to water resources layout, the data must be reverted. The reverting calculation methods are briefly summarized. And then some problems are produced. The conventional rainfall-runoff correlativity method and advanced projection pursuit are combined. A new method of hydrological serials revise, based on Projection pursuit, is produced. In this method the mountain functions in the style of multinomial are used, and program is easy.Chapter 3: The calculation method of water resources availableOne purpose of the water resources assessment is to answer the question of how much water is available. One-dimension water quality model is educed based on zero -dimension. In this method, actual water utilization quantity, contamination letting quantity and conflux are simplified. By the place of taking water, two methods, head controlling method and trail controlling method are produced to calculate the water resources available. A method to identify the contamination quantity, to confirm which is difficult, is produced.The basic demand to calculate the available water is gaining the ecological water requirements, which are required to keep the ecosystem healthiness. For basic purpose of the water resources assessment is to answer the problem of how much water resources are available, in this paper, the water resources available are summarized. When to confirm the water resources available, the Ecological Water Requirements must be considered. In this paper the studying status and confirming methods about ecological water requirements are briefly summarized. Ecological value and water resources utilization are combined. The calculation method of ecological water requirements based on theory of ecological economy is produced. In this method, ecological system and economic system are combined together by water resource. A new way is produced to develop water resources. And a new method is produced to study the ecological water requirements.Chapter 4: Testifying study about available surface water resources calculation in Heihe River catchment.Taking the middle reaches of Heihe River of the northwest inland discharge as an example, this chapter will testify the method produced in above chapters.The runoff data of the Zhengyixia Station is used to testify the reverting calculation method produced in chapter 2. The data of the Zhengyixia station and relating stations is used to analyzed by Projection pursuit revert calculation.The middle reach of Heihe River is compartmentalized into two parts. The two methods produced in this paper are used to optimizing calculation. And water available resources are gained. The result is reasonable, and can be used to direct water resources development in this region.Chapter 5: ConclusionIn this chapter, the methods produced in this paper and utilizing results are general summarized, and then some problems, which are not considered in this paper and which require to be studied detailed, and expected.
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