Reasearch On Rainfall Runoff Characteristics And Interception Methods In Typical Towns In Dianchi Watershed

In order to develop efficient interception facilities for intercepting initial rainfallrunoff,5typical sites in Chenggong area are chosen for researching rainfall runoffcharacteristics on sewage pipes of typical towns in Dianchi watershed. Water qualityand quantity on three typical underlying surface as well as three kinds of typical pipes,open channel in city village, branch conduit in combined system, separated system innew distract, respectively, are analyzed. Mean concentration of CODCr, SS, NH3-N, TN,TP, respectively in Chenggong Area are197mg/L,116mg/L,21.7mg/L,26.9mg/L,3.08mg/L, respectively. The concentration of SS will significantly increase in rainydays. Contaminants’ concentrations are in great differences between different types ofpipes. Even in the same sewage pipe, Contaminants’ concentrations of different rainfallevents are not the same. The values of indexes range widely. In terms of load changing,COD load and SS load are in synchronous change, so does to TN load and NH3-N load.The load in the same site may exist gap in magnitude in different rainfall events. Firstflush effects of open channels and separated system appear relatively significant. Toexplore the possibility of turbidity and conductivity as efficient closure devices’ controlindicators, correlation analysis between indicators were carried out. Results shows thatnutrient indicators are in good correlation. The correlation relationship between CODCrand SS or nutrients indicators depends on the form of CODCr. The correlation betweenCODCrand SS will increased with strong rainfall. Conductivity and nutrient indicatorsare in highly significant correlation. In all monitoring sites, correlation betweenconductivity and ammonia were above0.8, correlation between conductivity and TNwere above0.7. Turbidity and SS were in moderately or highly significant correlation.The correlation value will increased in strong rainfall events in particularly. On the basisof the correlation analysis, the regression equations between the quick monitoringindexes and traditional indicators were established. Fitting degree on the regressionequation of conductivity VS NH3-N, TN, TP respectively and the regression equation ofturbidity VS SS are high. Conductivity is about15.7times of NH3-N, and12times ofTN in Kunming.While conductivity is about13.3times of NH3-N, and11.5times of TNin Chenggong. Turbidity is about0.7times of SS in Kunming, approximately0.6timesof SS in Chenggong. Since one of the tasks on efficient interception facilities is theclosure of nutrients to slow down eutrophication in Dianchi Lake, so TN and flow were selected as indicators of efficient interception facilities. The efficiency of facilities andintercepting load with different indicators are calculated and compared. In the openchannel in city village, more than20%of volume is intercepted can ensure more than20%of load are intercepted. When50%of volume is intercepted,60%to77%of load isintercepted in open channel, and69%,70%,28%,63%,53%respectively of CODCr, SS,NH3-N, TN, TP respectively is intercepted in the separated system. The interceptionefficiency for TN or flow relies on their change relationship. Set Event8-2in theseparated system as an example, TN first drop down to3.3mg/L and keep for a periodof time, then drop down after increased slightly, so it can intercept the same load in thesame time. But in the open channel, TN first up to peak concentration value then dropdown to some low value. Select TN as indicator of interception facilities is moreefficient than flow when the intercepting volume is less than40%of the total volume.There would be no divergence if more than40%of the total volume were intercepted.