| In view of the problems of poor pertinence,inadequate consideration of ecological factors and poor real-time regulation in the process of determining the ecological flows of rivers in northern China.Based on the systematic analysis of the ecological hydrological characteristics and functional orientation of river system in Langfang City,the main problems existing in the river water system were identified.The thesis carried out the study of ecological flow(water demand)calculation and guarantee strategies based on the natural solutions,which was also based on the restoration goal of water body and riverbank habitat.The calculation of ecological flow in Langfang area started from the needs of the ecosystem itself,based on the theory of natural flow paradigm,and was completed within the framework of ecological-natural harmonious development.By screening the indicated species and their water-demand processes,the habitat simulation method and the Penman-Monteith formula method were selected by the stage layering method.Combined with the results of hydrographic and hydrodynamic methods,the thesis seeks to restore the naturalization state of rivers and restore the process of river ecological flow as far as possible.By evaluating the gap between the current flow and the target ecological flow,the measures to restore the ecological flow and close the flow gap were put forward.The research results of this thesis are of practical significance to make up for the lack of consideration of ecological factors in the process of studying the calculation of regional ecological flow,to improve the technical process of ecological flow calculation,and to enrich the management methods of the basin system.Based on the above analysis,Longhe River was selected as the research object.The main content and achievements of this thesis are as follows:(1)Based on the theory of natural flow paradigm,the theory of ecological flow determination based on natural solutions was proposed.Based on the concept and connotation of Nb S and the Nb S methodology related to the ecosystem,starting from the demand of the river ecosystem itself,it is assumed that the natural flow pattern is the ideal indicator of the ecological environment demand.The thesis proposed an ecological flow determination method based on natural flow paradigm theory,which makes the target river ecological flow process close to the natural hydrological situation value by simulating natural water flow,so that the determined ecological flow can support the water demand of most aquatic organisms and riverbank plants in the river ecosystem.(2)Taking pseudorasbora parva and reed as indicated species,using the habitat simulation method and the Penman-Monteith formula as the indicated species,the ecological flow process of the Longhe River,including ecological base flow,pulse flow during spawning period and flood ingress in flood season,was determined.Selecting pseudorasbora parva and reed as indicative species of water bodies and riverbanks,the thesis used physical habitat simulation model to simulate the relationship between flow changes and indicated fish habitat area,combined with the results of hydrographic and hydrodynamic methods.The thesis have calculated that the ecological base flow values of pseudorasbora parva of Longhe River in spawning period(April to June),nursery period(July to November)and growth period(December to March)were3.14m~3/s and 4.32 m~3/s and 2.16m~3/s,respectively.Based on the natural flow process and the water demand process stimulated by fish spawning,the thesis presented a pulse flow process that occurs at the end of spawning,with a peak flow of 11.31m~3/s for 7 days,and also suggested a small flood process lasting 3 days during the flood season with a peak flow of 24.95m~3/s.In order to ensure the water demand of the riverbank vegetation during the growth period of pseudorasbora parva,the thesis determined the ecological water demand of the various stages of reed growth by establishing the law of water demand change of reed plants with long-term life and setting the upper and lower limit thresholds of water level.The minimum annual ecological water demand of the reeds in the study river section was 151,000 m~3.(3)Based on the proposed ecological flow process,the difference between the current flow and ecological flow was assessed.The gap between the current flow of Longhe River and the flow status required to achieve the water demand process of the whole life cycle of the indicated species was also clarified.Based on this,the measures of ecological flow safeguard and strategies to maintain the basic ecological function of the river and realize the goal of river naturalization were put forward. |
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