| For a long time, the pattern of urban water system and water ecosystem has been severely damaged by the traditional urban construction mode. Low impact development aims to achieve the control of runoff and pollution from the storm by decentralized, small-scale source control, so that the development of the region as close to the natural hydrological cycle. Using rainwater as a supplemental source of landscape water can save fresh water resources, cut the total annual runoff and reduce the non-point source pollution caused by small rainfall. Using rainwater as a supplemental source will meet the green building evaluation standard, which requires using non traditional water source to supplement landscape water. It also improves the difficulty of the water quality assurance of the landscape water. The use of the baffled flow wetland system to construct an efficient water purification system can achieve the purpose of water ecological restoration.The water balance design and runoff pondage action of landscape water were analyzed; the water quality change of the micro rain storage facility was monitored and the pollution causes were analyzed; a baffled flow wetland- landscape water test device was developed, the factors affecting the water quality of landscape water body were discussed, such as the wetland area, the opening and closing of fountain, the cycle time and so on. The main research contents and conclusions are as follows:(1) Inflow and outflow of landscape water was calculated by month in the water balance design, and water balance calculation form was drawn. The rainfall was distributed according to Keifer&Chu rainfall pattern's principle, the inflow and outflow hydrograph was calculated by using finite difference method. Taking a construction area of Chongqing city as an example, the area of landscape water was 574 m2, accounting for the construction area of 1/87, 2 hours rainfall under the return period of 2 years, landscape water runoff pondage action: when landscape water normal depth was 1m before the rainfall, open the escape pipe, landscape water can delay strom peak 7 min and reduce the peak flow 35.1%; before the rain, emp tying landscape water facilities, open the escape pipe, landscape water can delay strom peak 31 min and reduce the peak flow 79.7%.(2) Experimental study on the change law of rainwater quality in rainwater storage facilities was carried out, the four conditions were the initial rainwater, the latter rain, ceramic rain, plant rain. On July 22, 2015, the concentrations of COD, TN, NH3-N, NO3-N and TP respectively were 35.90 mg/L, 1.57 mg/L, 0.26 mg/L, 0.23 mg/L, and 0.08 mg/L in initial rainwater. On the fourteenth day, there was an outbreak of algae, and the chlorophyll a concentration was 57.46 mg/m3. The correlation coefficient between the concentration of chlorophyll a and N/P ratio was 0.73. By the forty-second day, the water quality worse than the V class standard of surface water quality. After eight months, the concentrations of COD and TN were as high as 84.17mg/L and 7.45mg/L, respectively. The change law of water quality in the later stage was similar to that in initial rainwater. The concentration of the pollutants of the ceramsite rainwater was overall upward trend, but the concentration of pollutants was lower than that of the initial rainwater. The concentration of pollutants in the plant rainwater was basically decreased. Eight months later, COD, TN, NH3-N, NO3-N and TP concentrations were only 10.6%, 11.4%, 44.6%, 53.3% and 22.5% of the initial rainwater in the same period. The chlorophyll a concentration was always lower than 10 mg/m3, and the phenomenon of algal bloom was not observed. Q uality of water quality in different storage facilities(with total nitrogen and chlorophyll a): initial rainwater > late rainwater > ceramsite rainwater > plant rainwater.(3) Landscape water processing cycle was 3d, every day the fountain is open four hours. When the area ratio of wetland and water facilities were 2/15, 1/15, and the influent water quality was inferior to the V class standard of surface water quality, the device run a week, water quality can reach the IV class standard of surface water quality. The average turbidity of landscape water was 0.87, and the average chlorophyll a concentration was 1.74 mg/m3. The comparison test results show that the reoxygenation effect of fountain is obvious. Overall, fountain opening was conducive to the removal of pollutants, especially the removal of ammonia nitrogen increased significantly. When the processing cycle increased from 2d to 7d, that is wetland influent load was reduced from 3.8 m3/(m2·d) to 1.1 m3/(m2·d), COD, TN, NH3-N and TP removal rate respectively by 47.8%, 35.0%, 42.3% and 71.0% up to 75.6%, 46.1% and 65.7% and 87.5%, the effluent indexes meet the surface water class IV water quality standards. There was no significant difference in the removal rate of the pollutants in the same treatment time. Overall, the removal rate of pollutants was slightly better than other cycles when the processing cycle was 3d.Theoretical analysis and experimental study have been applied to the design, operation and maintenance of water quality control and water quality maintenance of landscape water in the construction area, in order to provide reference for the later practical application. Landscape water facilities can achieve the purpose of reducing the total runoff and peak flow through the rational design and operation management system. The proposed design parameters of landscape water facilities: wetland area accounts for 1/15-2/15 of water area; fountain regularly open every day; May to October, the processing cycle is 3d, November to April, and the processing cycle is 5-7d. |
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