The Field Investigation Of Habitat And The Research Of Hydrologic-hydraulic Characteristics Of Spawning Ground Of Ayu In Nanxi River

Nanxi River is located in the north of downstream of Oujiang River which is flow through Yongjia County of Zhejiang Province.There is excellent natural condition,pleasant landscape,unique human landscape and abundant fish resources in the Nanxi River River Basin.Among them,Nanxi River Ayu is famous migratory fish in history.In recent years,caused by human activities,Ayu is on the verge of extinction.This research is focus on exploring the reasonable way of water resources exploitation and protecting Ayu's habitat in the background of ecological civilization construction in china.At the same time,this work can maximize the ecological function and social service function of Nanxi River and Promote the formation of new river exploitation model and green development model based on the theory of human-water harmony.This paper takes the Ayu as target species,Ayu's habitat and its hydrologic-hydraulic characteristics of spawning ground in Nanxi River are studied by the methods of data analysis,field investigation and numerical simulation.The main research contents and conclusions are as follows:(1)Survey and appraisal of water quality in Nanxi River.Survey indicators include:pH,water temperature,transmittance,DO,COD,NH3-N,TP,TN and so on.The results showed that the water quality of upper reaches of NRWSP(Nanxi River Water Supply Project)is good,each sampling point is weakly alkaline,the DO concentration is high,the water temperature is suitable,the transparency is good,the concentration of NH3-N?TP?TN is at normal level.The lower reaches of NRWSP is tidal river,the sediment concentration is high,the transparency is low,the DO concentration is low,the concentration of TN and TP is high and COD is seriously overweight.Overall,the water quality of upper and middle reaches of the Nanxi River is good,and the water quality of lower reaches of NRWSP is relatively poor.(2)Aquatic organism suvey of mainstream in Nanxi River.Survey contents include phytoplankton,zooplankton and zoobenthos.There are 68 species of phytoplankton,belonging to 6 phyla.Of these,39 species are Bacillariophyta which is the dominant species.There are 16 species of zooplankton,mainly species are copepods and rotifers,the proportion is 32%and 31%respectively.There are 14 species of zoobenthos,mainly species are aquatic insects,the proportion is 50%.Overall,in the mainstream of Nanxi River,the abundance of phytoplankton is high and the diversity of zooplankton and zoobenthos is low(3)Hydrologic regime analysis of mainstream in Nanxi River.Using IHA indexes system to analyze daily average flow of Shizhu hydrologic station.The result shows that from 1957 to 2012,the flow of Nanxi River mainstream is less significantly declined.During the year,natural flow curve has 2 peaks,the former peak is generally formed by plum rains in June,the back peak is formed by typhoon in Augest and September.During the flood season,there are many flood peaks with shorter duration.In the non-flood season,the low flow occurs less frequently,but the single duration is longer.(4)Analysis of hydrologic characteristics of Ayu's spawning period.Combining the IHA indexes system and key hydrological process,screened 25 hydrological indexes and analyze the hydrologic characteristics of Ayu's spawning period(September-October).The result shows that during the spawning period,the daily average flow of Nanxi River is wave-likely declined.The processes of high flow and low flow occurred alternately,the duration is both short.The key flow falling process is much more than the key flow rising process.(5)Influence of flow change on the position and area of Ayu's spawning grounds.Take water depth(0.5-1.0 m)as the decision condition.Calculate the position and area of Ayu's spawning fish at different flow.The results show that when the flow rise,The spawning position is changed from the deep pool to the riffle at first,then gradually to the beach land on the shore.While under the same conditions,the spawning ground's area increased at first and then decreased,the maximum value occured in the flow of 75m3/s.(6)Analysis of hydraulic characteristics of Ayu's spawning ground.Take the annual average flow of 77.25 m3/s in September as characteristic flow in Ayu's spawning period,analyze the suitable range of velocity,Froude Number,velocity gradient,kinetic energy gradient.The result shows that the suitable range of velocity is 0.43?1.07 m/s,the suitable range of Froude Number is 0.19?0.48,the suitable range of velocity gradient is 12.881?14.466 s-1,the suitable range of kinetic energy gradient is 9.237?9.88J·kg-1·s-1?...