| At present,most of the engineering-constructions for sponge cities in China are carried out in the urban parcel-based catchments,and the quality and quantity of surface runoff can be controlled by several Low Impact Development?LID?facilities.However,there are few reports on the generation and control effect of urban diffuse pollution of the scale.In this study,two areas with different hardening rates were compared to analyze the characteristics of street dust accumulation and wash-off,surface runoff pollution and the effect of LID facilities on the flow and pollution load of the catchment.The main research and results are as follows:1.The road surface in the catchment was the main underlying surface type of street dust accumulation.The accumulated amounts of unit area in medium hardening rate?61.1%?and high hardening rate?73.6%?plots were 2.22?12.51 g·m-22 and 4.99?33.43g·m-2,respectively,which accounting for about 88.4%and 90.1%of the total accumulated street dust of the plot.The street dust<105?m as the significant particle size range for potential washing-off and pollutants enrichment had a higher mass ratio of the road and roof surface in high hardening rate plot than that in medium hardening rate plot about24.4%and 26.4%,respectively.2.With the impact of rainfall erosion,the washing dust of the urban parcel-based catchment mainly came from the road surface.The wash-off loads of road deposited sediments in medium and high hardening rate plots were 0.97?7.34 g·m-22 and 0.92?18.77g·m-2,respectively.The average wash-off percentages were 48.9%and 38.8%,respectively,and the proportions of scour mass were 91.7%and 90.5%of the catchment respectively.The washing rate of dust in smaller particle size from high hardening rate plot was significantly higher than than that form medium hardening rate plot.And the washing rate per unit area of<105?m dust in road and roof surface averagely increased by 106.4%and 160.2%,respectively.3.The distribution of surface runoff pollution load showed some differences on the two kind surfaces.The pollution load distribution of SS,TP,COD and TN in the surface runoff mainly came from the road runoff which accounting for 95.2%,98.1%,90.0%and79.3%in the medium hardening rate plot,respectively,and they accounted for 83.1%,95.0%,74.5%and 56.8%in the high hardening rate plot,respectively.However,for the load distribution of Cd,Cr,Cu,Pb and Zn,the contribution proportions of roof runoff were increased significantly,which were 18.3%,36.5%,23.6%,22.9%and 20.7%in the medium hardening rate plot,and 50.7%,17.5%,50.4%,6.1%and 57.7%in the high hardening rate plot,respectively.4.On the scale of the urban parcel-based catchment,after the treatment of the LID facilities,the total runoff reduction rates were about 69.4%and 56.5%,the pollution load?SS?control rate was about 76.0%and 59.9%in the medium and high hardening rate plots,respectively.The runoff particle size distribution was mainly<50?m,and the removal of runoff particles by the combined LID facilities was mainly for large particle size particles?>200?m?. |
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