Advancement And Assessment Of Low Flow Hydrology

Just like flood, low flow is one important part of hydrology and belongs to extremum hydrology. Having little influence on human at first, the research level of low flow is much lower than that of flood because of few attentions. With the rapid development of social economy, the problems of water resource shortage make low flow study attract more and more attention. Especial for the dry areas, the main characteritcs of low flow are important parameters for water supply engineering programming, water resource optimum scheme and rational protection.In this paper, the literatures and the advancedments of low flow study in recent years were reviewed and summarized. The computing methods in ungauged basins and the diversity relationships were also introduced and discussed. Four important aspects, including low flow forecast, frequency analysis, base flow separation and ecological water demand in river were studied. The main content of this thesis can be summarized as follows:(1) The convention low flow forecasting or prediction methods and assessment criterion were introduced and presented. The application of low flow forecasting or prection in humid and semi-humid basins was investigated.(2) The distribution form and the selection methods in low flow frequency analysis were introduced. The methods of PPCC and intuitionistic comparison were selected to distinguish the four assumed parent distributions through the analysis of six gauged low flow sequence with different durations(3) The concept of base flow is discussed. Several discharge hydrograph separation methods were analyzed and the existing problems were pointed out. These methods were compared by means of analyzing physical and runoff generation and flow routing process.(4) The basic theory and methods of ecological water demand study was reviewed. The data preperation, ecological situation, application condition, and limitations of these methods were compared and evaluated. The relationships among ecological water demand, pollution and biologic diversity were investigated and calculated in the Han river.