Effects Of Spur Dikes On The Fish Habitat In The Deep-water Channel Project In The Yangtze River Below Nanjing

The Yangtze River is both a golden waterway and an important fishing area.Large-scale waterway regulation project not only improves the navigation capacity of waterway,but also takes into account the impact of the project on fish habitat.Based on the 12.5m deepwater channel construction project of the Yangtze River below Nanjing,the Yizheng Waterway was selected as the research reach.Combining with field investigation,data consulting and expert consultation,the spatial distribution and habitat requirement of fish population and its "three fields and one passage" were discussed.In addition,the influence range of groins on fish"three fields and one passage" before and after the project was calculated,and the influence law of groins on fish early development was analyzed;the suitability evaluation model was established,and the suitability variation law of representative fish before and after the project was revealed by the suitability distribution map.The comprehensive effects of the groin group on fish habitat were obtained.The main conclusions of this study are as follows:(1)The general situation of fish population and habitat in the study area were summarized.There are many feeding fields in the nearshore shoal area in the channel,the upstream reproductive migration channel of coilius is in the main stream area,and the descending river migration of larvae is mainly in the nearshore area on both sides of the channel.The concentrations of phytoplankton in the river reach were relatively high,among which most species of phytoplankton were algae.(2)The rule of impact of ding dam group on fish habitat in waterway regulation engineering was revealed.The complex flow structure near the spur dam is suitable for the drifting fish to lay eggs.Provide a place and a feeding area for fish after the dam;The lower layer of the dam provides a good water environment for fish to survive the winter.Under the effect of dam head regulation,the range of slow flow area is obviously expanded,which is beneficial to the descending river migration of fish eggs and larvae.(3)The paper reveals the variation law of fish suitability before and after the project in the study area,the adjustment of river flow structure in the renovation project is local,and the dam head jet flow area and the dam behind slow flow area are formed near the spur dam.The head submerged embankment and the spur dike group on the southern edge of shiye continent reduced the original river flow rate,which is suitable for the development of coilia coilia fish,and the near-shore shallow water habitat of the two regions significantly increased.(4)The comprehensive health and ecological integrity of river reach were analyzed and studied,the fish integrity index f-ibi value gradually increased with time.The value of b-ibi indicates that the evaluation result of river reach is close to the healthy minimum value,reflecting that the engineering area provides more suitable living environment for fish.