| At present,there are 30 cities in China have carried out spongy city pilot construction,but the response of LID runoff regulation to rain type has not been comprehensively analyzed in most of the pilot areas.In this paper,the rainfall runoff of sponge city in Xixian New Area is taken as the research object.The hydraulic model of sponge city test platform is built,and the influence of LID measures on runoff regulation under different rainfall conditions is simulated,and We come to a preliminary conclusion.According to the measured results,the rainfall management model(SWMM)is constructed and simulated on the basis of the measured results.The model of rainfall Management(SWMM)is built to simulate different recurrence periods(once in a year,once in five years,once in 20 years,and once in 20 years),different rainfall duration(1h,5h)and different peak ratio(single peak 0.2,single peak 0.8 and double peak 0.5)under the design of rainfall conditions,LID measures are different from the initial saturation of rainfall runoff,and the effect of rain type on the flow rate under the control of LID measures is obtained.The two-dimensional numerical simulation area for the key area of Xixian New Area is built by using GAST model.And then we use GAST to calculate,the location,area and depth of waterlogging point are obtained under different rainfall conditions.Through numerical simulation,the improvement degree of the urban waterlogging in the key areas of the spongy city in the Xixian New Area is obtained in the different rainfall conditions and the different rain types at the same recurrence period.Then the Mat Lab software is used to visualize the location,area and depth of the waterlogging point,to visualize the distribution and variation of the waterlogging,and to further verify the simulation results of the SWMM model.The main conclusions of the study are as follows:(1)The waterlogging area such as Qinhuang Avenue has serious water accumulation before LID reformation,and there is still a large amount of water after the end of rainfall.After being transformed into LID measures,Rain Water entered all the biological detention facilities on both sides of the road completely eliminated the stagnant water on the road surface.It can be seen that after the completion of LID measures,the effect of urban waterlogging control is obvious;in the process of LID measures reformation,the green belt on both sides of the road will be excavated so as to form a certain water storage space,Rain Water will converge in and realize the effect of regulation and storage.It can be seen that LID measures can also reduce the degree of waterlogging in the reformation process,and the observation shows that the maximum hydrological area can be reduced by 33.7%.In the area where LID measures were not carried out,the two rainstorms formed a similar degree of waterlogging water,which proved that sponge city construction can effectively alleviate a certain degree of waterlogging water by controlling rainfall runoff reasonably.It can be seen that LID measures have certain application value in solving urban waterlogging problem.(2)At the same rainfall peak position,the longer the rainfall duration,the larger the runoff,and the longer the runoff,the lower the total runoff control rate is,and the runoff control rate is about 50% once in 50 years.The control rate of rainfall runoff once a year is as high as96%.With the same rainfall duration and the same recurrence period,the runoff of the post-peak rainfall is the largest and the control rate is the lowest.The runoff of bimodal rainfall is the smallest and the control rate is the highest.Under this simulated condition,the control effect of LID on double peak rainfall is the best.With the increase of recurrence period,the effect is more and more obvious.(3)At the same peak position,the longer the rainfall duration,the greater the peak flow,and the longer the recurrence period,the greater the peak flow,and the higher the peak value of single peak rainfall duration is compared with that of short-duration rainfall peak under the same recurrence period.The bimodal rainfall duration rainfall is lower than the short duration rainfall peak.Compared with the different rainfall pattern of p=5 and p=50,the rainfall peak value of the single peak rainfall is about twice that of single peak rainfall and double peak rainfall,and the difference of peak flow between front peak rainfall and double peak rainfall is not significant.P=50 is the peak flow gap before the peak rainfall and rainfall in double peak during the long duration rainfall before the peak slightly higher.At this time,that the best LID measures on double rainfall peak effect.P=5 is the peak reduction effect of LID was the best.In a word,the effect of LID on the peak reduction of rain peak is not obvious.(4)The runoff of short duration rainfall is significantly higher than that in semi-saturated state,which is much higher than that in unsaturated state.With the increase of recurrenceperiod,the increase of short duration rainfall runoff decreases gradually,with r = 0.2 as an example,the increase of unsaturated state is 122%,52% and 34%,respectively.The results show that the decrease of runoff is 79%,35% and 24%,respectively.In the saturated state,the control effect is more obvious for long-duration rainfall runoff control.The lower the increase of the recurrence period,the lower the increase of runoff.The change of initial saturation degree to rainfall runoff with large recurrence period is not obvious.When the LID measure is in the unsaturated state,the runoff of the front peak rainfall is generally slightly smaller than that of the latter peak rainfall,while when the LID measure is in the semi-saturated state and the fully saturated state,the runoff of the front peak rainfall is generally larger than that of the post peak rainfall and the two-peak rainfall.The effect of runoff control on the post peak rainfall is the best,which is due to the fact that the latter peak rainfall provides time for Rain Water's permeation and absorption under the condition of semi-saturation and full saturation.However,the peak of rainfall came quickly when the former peak rainfall came,Rain Water in the LID measure had no time to penetrate and absorb.So the semi-saturated state and the effect of Lid on the runoff regulation of fore-peak rainfall is poor when it is fully saturated. |
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