A Study On The Concept,Method And Adaptive Management Of Environmental Flow In Plain River Network Region

Environmental flow is the cornerstone of rivers with the ecological and environmental functions.It has been widespread studied at home and abroad, but there were less research at plain river network region. Base on review of research progress and available methods, the definition of environmental flow of plain river network region was brought up, that the flow to maintain healthy, natural ecosystems, protect rivers' biological diversity and meet the demand of basic environmental function at the target of reality of water-function regionalization, according to the characteristics of plain river network, such as flat terrain, rich water, poor water quality, artificial control. Its basic connotation is as follow: (1)Environmental flow is an flow interval closed to the natural fluctuations, with Minimum ecological discharge for lower limit and restrain to local flood control standards for upper limit. (2)Environmental flow is characterized by magnitude and direction, and could be classed by its volume and quality. (3) Environmental flow is specified to river with ecological and environment functions.Environment flow have spatial scale and time scale, the spatial scale of environment flow for plain river network region are the main rivers of the basin, water conservation region, middle and small rivers with ecological and environmental functions. The temporal scale is year and the specific water demand period of ecosystem and environment. On the base of identifying the water demand elements, calculation methods of environment flow of plain river network region were collected. The environmental flow study considered both water quantity and water quality, which is based on the identification of ecological and environmental water demand elements for plain river network region and the calculation methods of environmental flow for rivers and water conservation regions. Month assurance method is used for water quantity calculation, DO is the calculation object for water quality under the principle that quality is prior to quantity. 36 combinations, which include not only fixed ratio between water quantity and water quality but also dynamic weight arrangement according to the shortage degree of both, are discussed and 4 types of basic flow modes and 5 classification are determined. The result showed that dynamic weight method is better in accordance with the real situation to get an ideal environmental flow.Calculation and evaluation of environmental flow for the North Jiabao region in Shanghai showed that the maximum water demand lies in water quality, other ecological and environmental water demand could be satisfied once waster supply is guaranteed for its resource function. However, there is still too bad water quality exist for some local rivers to exert their ecological and environmental functions even if the environmental capacity is satisfied with water function (environmental) regionalization requirement. Therefore, more precise information for river network is required for the future further study to get better ecological and environmental benefits, and also more effective deployment for environmental flow is required.Experiment of employing adaptive management mode to environmental flow deployment suggested that it is very good at the work flow analyzing and flexible arrangement, according to the real flow states, for environmental flow to effectively support the long-term environmental flow management.