Research On The Impact Of Sponge City Land Use On Surface Runoff

To explore the impact of land use on surface runoff during the practice of sponge cities,guide the construction proportion and layout of sponge facilities in urban construction land,thereby solving the current increase in surface runoff and runoff pollution.This article takes the country's first sponge city pilot project,Jiaxing City,as an example.It selects 20 projects within the demonstration area that have different land use properties and sponge construction levels as research units to establish land that can reflect the proportion,types,and layout of sponge facilities.Using indicators,and using methods such as Spearman rank correlation analysis,multivariate statistical regression model,redundant analysis,partial least squares method and Origin fitting equation to qualitatively and quantitatively explore the impact of land use indicators on surface runoff and runoff indicators,Screen out key impact indicators to provide effective basis for rational planning of land use structure.Through research and analysis,the following results are obtained:?1?On the whole,the construction of sponge city has played a positive role in reducing surface runoff and improving runoff water quality.Sponge facilities have the most significant effect in controlling runoff under moderate rain intensity.Under different rainfall intensities,with the change of rainfall duration,the overall trend of the surface runoff modulus?the runoff per unit time per unit watershed area?in the sample land is basically the same.The value increases with the increase of rainfall intensity.Increased;under the same rainfall intensity,the peak value of the runoff modulus in the transformed samples of the same land property is lower than in the unmodified samples.The magnitude of the surface runoff modulus,peak value and runoff coefficient in each sample land under different rainfall intensities are:torrential rain>heavy rain>moderate rain.When the average rainfall intensity is moderate rain,the surface runoff water quality in the modified sample of the sample land of the same nature is better than that in the unmodified sample.The water quality of the park land is the best,the residential district is the second,and the water quality of the public building is obviously poor In the former two,and the water quality of residential quarters and public building areas did not meet the surface water category IV and sewage discharge secondary standards.?2?According to the results of Spearman rank correlation analysis,the ratio of green land,ineffective impervious area?IIA?and weakly impervious surface is significantly negatively correlated with surface runoff coefficient,and the effective impervious area?EIA?and total impervious area?TIA?ratios are significantly positively correlated with surface runoff coefficients.Except for IIA and runoff coefficients,which are weakly and significantly related,other land use indicators and surface runoff coefficients are strongly significant correlation;the results of redundant analysis show that the proportion of green land,IIA,and weakly permeable subsurface is negatively correlated with water quality indicators,and the proportion of EIA is positively correlated with water quality indicators.Among them,the water quality indicators highly related to land use indicators are SS,BOD₅,COD and NH₃-N.?3?According to the results of the multivariate statistical regression model analysis,it can be seen that the nonlinear regression model of land use types and surface runoff coefficients has a better fitting effect than the linear regression model,and quantitatively explores green land,EIA,and weakly permeable area.The fitting equations of the proportion and the surface runoff coefficient under different rainfall intensities are compared and found that the fitting effect under the moderate rainfall intensity is the best;the partial least square method is used to quantitatively calculate the different land use indicators for various water quality Contribution of the index,and found that the proportion of green space and EIA has the greatest impact on SS,BOD₅ and COD in water quality indicators.?4?Using Origin software to fit and predict the change in the relationship between the land use index and the surface runoff coefficient,it is found that?1?Among the land use indicators that affect the surface runoff coefficient,EIA,green space,and weakly permeable subsurface ratio affect the surface runoff coefficient in order.Decrease;?2?In the unreconstructed sample land under the ratio of conventional green space?approximately 35%?,when the EIA ratio exceeds 30%,the fitting relationship between surface runoff coefficient and EIA ratio changes significantly;?3?in the ratio of conventional green space In the transformed sample land below,when the EIA ratio is between 60%and 75%,the surface runoff coefficient is gradually increased by the influence of the EIA ratio;?4?Under the condition that the EIA and the ratio of the weakly permeable water surface remain unchanged,when the ratio of green space exceeds 32%,the degree of influence of the ratio of green space on the surface runoff coefficient gradually increases;?5?When the ratio of green space and EIA are higher and lower,and the ratio of the two is unchanged,when the ratio of weakly permeable water cushion surface exceeds 15%,The degree of influence of the ratio of weakly permeable subsurface to surface runoff coefficient gradually decreased.?5?By controlling the key indicators in the land use type-the proportion of green space and the proportion of EIA,and using the Origin software to fit and predict the relationship between the key indicators and the quality of runoff water,the results are as follows:?1?The proportion of green space and EIA affects the quality of runoff water Key factors,among which SS,BOD₅ and COD are the main affected indicators.?2?In order to make the quality of runoff water meet the requirements of sponge city construction,there are differences in the thresholds of the indicators that need to be controlled at different sponge levels,which are mainly divided into the following three cases:When EIA?0,the proportion of green land should not be less than 31%;EIA=0.04?TIA?^1.7,the response threshold of the green space ratio is 38.5%;when EIA=TIA,the response threshold of the green space ratio is 47%;under the conventional urban green space ratio?about 30%-35%?construction standard,the response of the EIA ratio threshold is 9%.