Calculation Methods Of Channel Regulation Design Parameters In Alluvial River

Occidental experiences in navigable channel improvement history show that compulsive regularization can not change the inherent evolution characteristic of river bed fundamentally. Excessive interference in river natural attribute will bring serious problems inevitably. The more scientific means of channel regulation is that with to consider flow & sediment process and river bed evolution rules, building few projects assisted river characteristic with guiding it to improve navigable conditions.So it is necessary for regulation parameters calculation, as the basic of shoal regulation project, to reflect river evolution characteristic, scour and aggradations rule of shoal and navigable channel grade, and to use expediently. Furthermore, the river bed downstream dam is in a disequilibrium process to adapt variance of flow & sediment. Shoal evolution rules will have some changes and bring navigation conditions more new problems. Even some reaches are going to be worst. Therefore, the disequilibrium conditions downstream dams request the means of calculating regulation parameters more strictly.The key points of determining channel regulation parameters are to be assured that regulation works conform to the common rules, and at the same time to solve special problems of the reach. But now many researches on the relationship between the regulation design parameters of shoal in dry season and river bed evaluation rules aim at certain local reach. So there is lack of comprehensive results. Though the methods of determining regulation parameters develop gradually, their pertinences and rationales are still unconsummated. As a result, the outcomes of different methods are six to one. Even they are unable to apply in some complex sections.This paper analyzes the channel regulation theory and improves the determination methods of the channel regulation and design parameters. Considering river bed evolution rules and functions of regulation projects, the researches in this paper try to connect the flow & sediment process, the changes of riverbed, shoal evolution, which are the reasons to cause aggradations, with the design water level, regulation parameters, regulating structure, which can eliminate sediment on shoal. The influence factors can be simplified so that the typical variables are introduced into the method of regulation parameters calculation. So the improvement method can reflect the characteristic of flow & sediment, shoal type, evaluation rules and navigation grade. Even if the regulated reach was under the disequilibrium condition downstream dams, the method still would be suitable by choosing reasonable variable values.Main work in this paper can be divided into four parts: firstly, finding the linkage between the results of the river dynamics & river bed evolution research and the channel regulation theory in order to consummate the theory system of regulation parameters from the basic concepts; secondly, discussing the theory support and the insufficiency of each determination method; thirdly, proposing the guarantee rate concept of regulation works through analyzing evolution rules of different type of shoal and the influence factors of parameters determination, and putting the guarantee rate, channel obstructive quantity and effective scouring time, which can reflect shoal characteristic and channel navigation grade, into the method to computer the regulation parameters; fourthly, establishing the regulation width formula for different type shoal and the rivers dynamics unified formula. Most work is with the background of the middle and lower reaches of the Yangtze River, and application of the new method shows that the rebuilding formula could be applied to calculate the regulation width of complex reaches. Some key issues are shown as following.(1) The relationship among Flow & sediment process, riverbed evaluation and regulation works design indicates that the revision and supplement to the design theory is needed. It is necessary for the development of channel regulation that the methods to compute the design parameter and the regulation parameters should be able to reflect the channel obstructed characteristic and river evaluation rules.(2) The general characteristics of flow & sediment transport and river bed evaluation under the equilibrium condition are clarified. As contrast, the changes of flow & sediment process and river bed evaluation are analyzed under the disequilibrium condition. From the angle of convenience use in channel regulation, shoal types and their evolution rules are analyzed. In those foundations, shoal evaluation specialties downstream dams are summarized. It is useful to propose the variables into formula improvement.(3) In the paper, a description of the methods of calculating design lowest navigable water level is given. The differences between guaranteed rate method and guaranteed rate–frequency method on the fundamental concept of guaranteed rate and the calculated result are carried out. According to the theoretical expression forms of the two methods, the new ways to get uniform results are proposed. This paper calculates the design water levels of some hydrometric stations in the middle and lower reach of the Yangtze River by the guaranteed rate method and compares them with the results of the guaranteed rate–frequency method. Those results show that the design water levels have changed in the past twenty years. With extending the concept of design water level from the equilibrium river into the disequilibrium river, the design water level line method is proposed on the basis of the flood routing through reservoir and one dimension numerical model downstream dams. As an example, the design water level change line is figured out downstream of the TGP (Three George Project) and the reasons are analyzed.The concept of guaranteed rate is used in the design water level, but in fact, it runs through the whole process of regulation works design, including regulation line, regulation water level and regulation widths. Flow & sediment process can be simplified by choosing some guaranteed rate, which indicates the interaction between regulation works and river bed. (4) With river control as precondition, the paper analyzes the basic problems on channel regulation parameters. Starting from the specialties of regulation works, we differentiate its concept from river dynamics and outline the factors effecting on regulation parameters and the types of regulation works. Different from absent knowledge, it is elucidated that the design of regulation line is the basis of regulation width and regulation water level and that different design has different channel obstructive quantity and shoal scour time, so that there is dissimilar regulation width and corresponding water level. We discuss the design principle on different shoal type, and establish a regulation line formula to decide the length of the transitional reach, which is well used in the middle reach of the Yangtze River, by introduce the circumfluence disappearing theory.(5) Summing–up the existed methods of regulation water level in the send–bed river, their applicability and comparability are analyzed. With the regulation works in the middle and lower reaches of the Yangtze River, the shortcomings of each regulation water level method are showed clearly and the more applied methods are point out. Though analyzing the characteristics of regulation water level calculation methods downstream dams, this paper brings forward the method that is according to the flow character downstream dams, choosing two grade regulation charges with high guaranteed rate and picturing the corresponding regulation water level curve changing with river bed.(6) The existing methods of regulation width can be divided into three modes. With analyzing respective theory basis and contraposing the section's scour and deposition pre– and post–regulation in the straight river reaches, meandering river reaches and bifurcated river reaches, shoal evolution characteristic variables, which are channel obstructive quantity, shoal scour time and regulation guaranteed rate, are introduced into regulation width formula so that a new river dynamics unified formula is established. And it can be used in various guarding regulation works or adjusting regulation works. The regulation widths of the Nianziwan waterway, the Luxikou waterway and the Wuqiao waterway are respectively calculated by using the unified formula. If we divided channel obstructive quantity into two parts, caused by undulation of flow & sediment process and caused by reservoir, that regulation width formula can be used still downstream dams by accounting deposition and choosing some guaranteed rate.(7) According to different fundamentals of guarding regulation works and adjusting regulation works, several familiar regulating structures can be divided into two groups. This paper analyses their respective layout, structural styles and main actions.