Study On The Naturalization Of Biological Habitat Based On The Arrangement Of Gravel Groups In The Meander Cutoff Channel

In the process of the continuous development of urbanization in our country,the social economy has also achieved unprecedented development.In order to resist the flood,or the development of waterway,or the urban expand,people have taken the river remediation measures of meander cutoff,In addition,the natural meander cutoff of rivers also causes greater damage to the habitats of organisms.In order to evaluate the impact of river meander cutoff on biological habitats in the process of urbanization,to explore the effect of gravel groups on the naturalization of river habitats,and to study the ecological water demand of rivers with cutoff channel gravel groups.Taking Jinsha River as an example,using literature research and numerical simulation methods,the regional dominant fish species-silver carp was selected as the target species,coupled with the planar two-dimensional hydrodynamic simulation of the river section,The change of habitat quality of silver carp before and after meander cutoff was studied,and the effect of gravel arrangement on the habitat of silver carp was also studied.The ecological water demand of cutoff channel gravel group was also studied by habitat method.research shows:(1)By meander cutoff the original river,the water level of the inlet and outlet section is reduced by 0.64m and 2.23m respectively,and the flood water level of the first flood in 20 years is dropped significantly,which effectively solves the problem of flood control in the study area.The weighted usable area of silver carp habitat in the cutoff channel decreased significantly,and the percent usable area of silver carp decreased sharply from 17.99%of the original river to 9.20%.The flow Fr increased significantly near the main streamline of the original river,and the shear velocity value changed from the transverse gradient distribution of the original channel to uniform distribution.The meander cutoff not only dredged the channel to reduce the flood water level,but also destroyed the flow pattern of the original river channel,which worsened the flow pattern of the river and reduced the living space of silver carp.(2)By arranging gravel groups in the meander cutoff channel,the percent usable area of silver carp habitat increased from 9.20%to 15.06%in the cut-bend river concave bank with the highest density,and the Fr of the water flow near the downstream of the gravel group decreased from 0.13～0.40 to 0～0.27,the value of shear velocity decreases from 0.11～0.16 to 0～0.11 in the cutoff channel,and the downstream area of the gravel group forms a low-speed water flow area.And set a fixed point in the middle of the river channel to compare the Fr of different layout densities at the same location,which are 0.46、0.47、0.48.It is believed that as the layout density increases at the same location,the flow velocity in the mainstream area of the river channel will also increase,and the area with smaller Fr in the river will gradually increase.The gravel groups arranged in the middle of the river and on the convex bank produce a suitable habitat for silver carp,so the arrangement of gravel groups creates a suitable living environment for silver carp,and has a significant effect on the naturalization of the silver carp habitat.(3)Based on the orthogonal experiment design,through the analysis of range and variance,it is considered that the order of the influence of various factors on PUA is as follows:River discharge>Side length of gravel accumulation body>Gravel accumulation spacing;When the side length of single gravel accumulation body is 20m,the spacing is 9m,and the discharge is 1418m~3/s,it is the best gravel group characteristic and river discharge combination.By setting different discharge conditions,it is concluded that the ecological water demand of the original river course is 718m~3/s,and the ecological water demand of the cutoff channel gravel group is618～696m~3/s.The arrangement of gravel groups protects the stability of silver carp habitat,and the amount of water required to reach the best condition of the silver carp habitat has been reduced,providing a theoretical basis for ecological protection,water resource utilization and dispatch.