| In recent years, due to the rapid urbanization and ever-increasing population, the atmosphere and ground surface such as roof, lawn and road in urban areas are withstanding severer and severer pollution. In wet weather, a great many pollutantsare discharged into the receiving water.The urban rainwater runoff has thereby turned to be one of the main reasons which cause significant damage to the aquatic environment. Therefore, it is greatly needed to understand the characteristics of different surfacerunoff and optimize the drainage systems through models.First of all, the ranges and distributions of instantaneous and event mean concentrations (EMC) in rainwater runoff, the Pearsoninterdependency among various water-qualityindexes and the first flush effect were evaluated in Fuzhou City, Southern China. In all the14representative rainfalls, the surface runoff in residential areas of old district achieved EMC average values of95.5～194,2.57～3.33,0.75～1.39and149～240mg/L, respectively for chemical oxygen demand (COD), ammonia nitrogen (NH3-N), total phosphorus (TP) and suspended solids (SS). Meanwhile, the corresponding values for residential areas of new district were74.1～84.0,1.62～1.84,0.34～0.37and117～128mg/L. The pollution level of old districtobviously exceeded that of new district. Meanwhile, the SS showed a prominentPearsoninterdependency with COD. Furthermore, slightfirst flush effect was found in various sampling sites of Fuzhou City.Secondly, the effect of rainfall characteristics, rainfall types, urban surfaces, urban functional zones and drainage systemswere investigated in detail. Among the four rainfall characteristics, antecedent dry days showed a larger influence on rainwater runoff pollution than rainfall depth, rainfall length and maximum rainfallintensity. The instantaneousconcentration of pollutants also had an obvious relationship with rainfall types. Meanwhile, for the EMC values of COD, SS, NH3-N and TP, the following relationship was workable in residential areas of old district:direct rainfall<roof runoff<road runoff<sewer overflows while for residential areas of new district, it was:direct rainfall<roof runoff<internal road runoff≈external road≈sewer overflows. As for urban functional zones, the surface pollution level in residential areasexceeded commercialones and furtherexceeded administrative ones. Besides, the pollution level in intercepting combined systemsexceeded directly-discharged combined ones and further exceededseparateones. Thirdly,a new cost-effective mathematical methodnamed Contribution Partition Mathematical Method for Storm Sewers (CPMMSS) was put forward.Thismethod aimed to help communities to better understand the contribution of roof, internal road (IR), lawn andexternal road (ER) runoff, mistakenly discharged wastewater (MDW) and sewer deposit erosion (SDE) to wet weather flows (WWF) in storm sewers. Its case study on JinShan Site showed that the surface runoff was the greatest contributor of the WWF. For instance,ER provided as much as52.4±7.5%of COD,50.6±11.0%of soluble COD (SCOD),50.5±11.8%of dissolved organic carbon (DOC) and49.8±8.7%of TP. Besides, MDW and SDEalso played an important role in WWF pollution of storm sewers.In addition, the total pollution load from urban rainwater runoffin Zhenjiang City was evaluated and calculated. The results indicated that the total pollution load of total suspended solids (TSS), NH3-N, TP, COD, biochemical oxygen demand (BOD5) and total organic carbon (TOC) were25396,175.0,40.3,5718,2064and591.6tons, respectively. In terms of pollution-reduction measures, transforming combined drainage systems into separate ones performed better in reducing pollution load while cost the highest. Constructing combined sewer overflows(CSO) storage tanks demanded the lowest costs, but it could not reduce as much pollutants as the other two measures. Moreover, constructing a new interception pipe presented thelowest feasibility and cost-effectiveness.At last, the conception of "Intercepting Integrated Drainage System (IIDS)" was proposed, which was made up of three integral parts:pipe network systems in urban areas, intercepting trunk pipe systemssetting along the receiving water and wastewater treatment systems. IIDS wasfound to be feasible in both Fuzhou City and Nanping City. Furthermore, it could be adjusted and optimized based on the constraint conditions of the applied cities and regions. Meanwhile, the Infoworks ICM model of a selected catchment in Fuzhou City was built up. By this model, the floodingstatus of surface and overloadingstatus of storm sewers were simulated under the impact of different rainfalls. Thelimitingconduits were found out and optimized to improve the performance of whole drainage systems. |
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