Study On The Landscape Ecological Problems Of City Water System System In Yongchuan Region Based On The Theory Of Watershed Ecology

This paper,taking the city water system of Yongchuan as the research object,launches on three aspects.First,study on the relationship between the up-and-downstream and the city water system.Secondly,discuss the hydrological effect of city suburban catchment and its influence on the hydrological process of the city water system.Finally,analyze the structure characteristics of the city river system.The results are as follows:(1)Relationship between the up-and-downstream and the city water system.In the aspect of water quality,all the water quality of Yongchuan city water system failed to meet the standard of level V,except Tiaodeng River.Before flowing into the built-up area,The concentrations of nitrogen and phosphorus of Yongchuan River were 0.76mg/L and 0.09mg/L,however,when flowing through the city,the concentrations of nitrogen and phosphorus increased to 4.8mg/L and 0.45mg/L respectively,Which shows the deterioration of water quality.In the aspect of water quantity,the water quantity flowing into the built-up area from the upstream of Yongchuan River is 109429900 cubic meter per annum,accounting for 52.6%of the total;the input quantity of nitrogen with the upstream water is 83.17 ton per year and with 9.85 ton per year of phosphorus,accounting for respectively 84.4%and 75.3%of the total external pollutant input.The water quantity flowing out of built-up area is 36371500 cubic meter per annum,which is far less than the quantity that flowing into the built-up area from the upstream.The output quantity of nitrogen and phosphorus in the water are 174.58 ton per year and 16.37ton per year severally,which will pollute the downstream rivers.According to the analysis above,the upstream water quality reaches the standard of level ?,so there is no need to manage it.Flowing through the built-up area,the river water quality is worse than the level V,so an artificial wetlands is essential for purification,the construction area should be 24.3?36.4 million square meter according to the pollution condition.(2)Hydrological effect of city suburban catchment and its influence on the hydrological process of the city river system.The Yongchuan City catchment area is 159.2km,consisting of the Yongchuan River and its tributaries,the suburb catchment is consist of Yongchuan botanical garden catchment,Qinjian reservoir catchment,Sunjiakou reservoir catchment and Qiyi reservoir catchment,and the correlative downstream rivers are Yuping River,Tiaodeng River and Hongqi River separately.Using Qinjian reservoir catchment as the example to study the hydrological effects of suburban catchment and the effect on the hydrological process of the city river,the results are as follows:From 2009 to 2014,composition of land use types changed much within the Qinjian reservoir catchment:the urban land area increased 84.7 hm2,the bare landincreased 43.3 hm,while the farmland reduced 131.6 hm,the water area reduced 12.2 hm2 and the grassland decreased 29.6 hm2.However,the woodland changed little.These changes made the catchment runoff and peak flow increased,resulting in the high frequency of water flood;the water conservation reduced,namely,the ability of water supply to the downstream areas reduced;the amount of soil erosion increased,which means the deterioration of ecological environment in the downstream area.The scenario analysis shows that,if the city construction in accordance with the overall planning of urban and rural areas,it will severely weakened the flood control capacity,increase the soil erosion and the flood threat in built-up area;if the city construction speed is the same as the current speed,the hydrological effect will be better than the former?but compared with the tendency of 2009-2014,hydrological effect will still become worse and worse;if considerate the ecology priority,and try to limit the rate of city expansion,the water ecological environment will be improved.Therefore,the influence of city expansion speed on the hydrological effect should be considered during the progress of city construction,so as to take corresponding measures to protect the city water catchment area.(3)Structure characteristics of the city water system.In the built-up area,the total length of the green river corridor is 50.29km,the average width is 10.31m,the total area is 0.85km,and the corridor average construction rate is 62.14%.While in the city catchment area,the total length of the green river corridor is 131.71km,the average width is 18.71m,the total area is 4.16km2 and the corridor average construction rate is 64.17%.Data of the city catchment area is higher than that of built-up area,which means heterogeneity is higher and species diversity is more abundant and better in the city catchment area than that in the built-up area.In the built-up area,the blue corridor and green corridor index ? are 1.06 and 0.59 respectively,the index of y are 0.40 and 0.20,while the index a are 0.11 and 0.In the city catchment area,the index(3 are 0.85 and 0.62,Index ? are 0.31 and 0.21,the index a are both 0.The blue river corridor and green river corridor network structure are both relatively simple with low degree of connection,which are not conducive to the material and energy flow and the protection of biological diversity.In contrast,the network structure of blue river corridor is better than the green corridor,and the network structure in the city catchment area is better than that in the city built-up area.Aiming at these structural problems,measures should be taken to improve the structure of city water system.First,take the suburbs reach and built-up area into overall consideration,and then strengthen the riverside green space construction,last but not least,improve the river connectivity.