Research On Physical Habitat Improvement Of Channel In Qing Yi River Basin(Xuchang Part)

In this paper,Qingyi river basin(Xuchang part)was chosen as study area,aiming at physical habitat problems of single flow velocity,water depth and undiversified river habitat in Qingyi river basin,for the purpose of physical habitat improvement,firstlly,status of aquatic life,physical habitat of channel,velocity,depth and substrate were investigated and evaluated,then physical habitat improvement measures were proposed.Secondlly,construction parameters of habitat improvement technologies were optimized through MIKE21 two-dimension hydraulic model.At last,fish habitat model-River2 D were used to simulate overall effects of habitat improvement measures on Weighted Usable Area(WUA)of indicative fish,as effect verification of physical habitat improvement.The results could provide theoretical basis and data support for future river habitat improvement projects.(1)Through investigation of aquatic life in the basin,it was found that dominant species of aquatic plants were Potamogeton pectinatus L.,Phragmites communis,Typha orientalis Presl,and Potamogeton crispus,dominant population of large benthic animals were Chironomidae,Limnodrilus hoffmeisteri Bellamya purificata(Heude)and Radix auricularia(Linnaeus),Pseudorasbora parva and Carassius auratus dominanted the advantage in all species of fish.The above populations were local dominant groups with wide range of adaptation and strong reproductive capacity.Therefore,this research regarded them as target species for habitat improvement.Rapid Bioassessment Protocols(RBPs)was chosen to investigate and evaluate current situation of river physical habitat,flow velocity,water depth and substrate,it was found that physical habitat quality of Qingyi River upstream and Baling – Xiaoni River midstream was poor,and needed to be improved.Problems of physical habitat in basin were as follows.1)Upstream of Qingyi River was dry,and lacked ecological basic flow.2)Velocity and depth of basin were slow and shallow,rapid and deep area habitat essential for aquatic life was rare.3)River bed was mostly made of silt,lacked fine gravel and solid grit.4)Lacked pool and shoal sequences.5)River was manually intervened seriously,degree of habitat degradation was obvious,channels were straight and lacked point bars,exposed bedrocks,boulders,and other coverings,habitat type was relatively single,and quality was poor.To solve above problems,three kinds of technologies-groin systems,pool-shoal and weir/gravel groups were chosen,intending to change the status quo of slow velocity,shallow water and homogenization of velocity and depth,construct river coverings such as gravels,restore winding of river,etc.and improve habitat quality finally.(2)MIKE21 hydrauilc model was used to compare and optimize parameters of groin systems,pool-shoal and weir/gravel groups.The optimal parameters of groin was trapezoidal groin system with space of 10 m(about 2 times the length of groin),angles between upstream,downstream side and flow direction were 30°and 120°.Pool was set as class oval with long axis of 8 m,short axis of 5 m,whose bottom was laid with sand and pebbles,shoal was set as embossment with long axis of 8 m,short axis of 5 m,whose bed was made of boulder,pebble and riprap,which were optimal parameters settings of pool and shoal.Optimal parameters of weir/gravel group were as follows: weir with height of 0.8 m,upper base width of 2.0 m,bottom width of 4.4 m,upstream and downstream face gradient of 1:2 and 1:1,respectively,besides,the weir was composed of rubble with different particle size,whose upper layer was filled of big riprap particle size ranging from 20 cm to 30 cm,substratum was filld of small riprap particle size ranging from 10 cm to 20 cm.Every gravel group was made of 4 irregular and large gravels with diameter of 1.0 m,and space between gravels and gravel groups were 0.5 m and 10 m,respectively,placed at both sides of 1/3 of the deep line.The simulation of parameters optimizing showed that groin systems,pool-shoal and weir/gravels groups could increase diversity of velocity and depth of local channel,further more,improve status quo of homogenized velocity,depth,flow regime,and river coverings.(3)Two dimensional fish habitat evaluation model-River2 D was used to set habitat improvement measures,whose parameters were optimized in Baling River,to simulate and verify improvement effects on WUA of fish.The results showed that WUA was 15.4 times of the original river after setting groin system and other physical habitat improvement measures,effects of groin systems and gravel groups on improvement of cyprinidae fish's habitat were more apparent.Above all,groin systems,pool-shoal and weir/gravel groups with optimized parameters had a good effect on the improvement of physical river habitat.