Study On The Calculation Method Of The Volume And Interception Cistern Cubage Of Urban Early-stage Storm Runoff

The first flush effect on urban surface from the rainfall makes the early-stage storm runoff carry huge amounts of pollutants, and the direct emissions will have impact pollution to water bodies. Referring to the pollution control experience of developed countries, building interception cisterns of early-stage storm runoff is one of the effective ways to control urban storm runoff pollution, especially when we make urban landscape water bodies as the rain drainage receiving waters. And to kown the volume of early-stage storm runoff is the key to design interception cisterns.As a part of storm runoff, the confluence of early-stage storm runoff also follows the equel flowing time line principle — the flowing times to the confluence point of the rainwater that fell on the ground at the same time are different. Dividing one rainfall into two— early and late— the early-stage rainfall and the late-stage clean rainfall have inherited part of the regularity of the rainfall respectively, and we regard the runoff formed from the early-stage rain as first flush rainwater. After reaching a certain depth, the early-stage rain suddenly stop and the clean rain start at the same time, and then the early-stage rainwater continue to complete the confluence. Reflecting the relationships that the storm runoff flow and the initial storm runoff flow change over time at the confluence point on the curve is t he storm runoff and the initial storm runoff confluence model.The study has monitored the rainfall processes, the runoff proces ses and the water quality change processes of a residential area in Changsha city when it is raining, and it has piecewise fitted the runoff process curves and the water quality change process curves. Under the premise of considering the pollutant concentration decreace in storm runoff is the result of that early-stage rainwater has mixed with clean rainwater in the pipes, it has used mixed proportion to separate initial storm runoff flow from the storm runoff flow, and draw the initial storm runoff process line in the fitting curve of rainwater runoff process by u sing the graphical method, and then to determine the volume of initial storm runoff. The initial storm runoff volume of the three rainfall monitored by the study are 1.17 mm, 1.22 mm and 1.09 mm. Considering a certain allowance, it advises that the volume of the early-stage storm runoff in residential district in Changsha values 1.5mm.On the basis of kowning the design volume of the early-stage storm runoff, the study puts forward a kind of calculation method of the interception cistern cubage using the confluence model. Its design principle is that increase the initial rainwater collection rate as much as possible on the premise of a guarantee of a certain interception cistern utilization rate. The significance of this calculation method lies in that it has considered the actual rainwater confluence process, and it is a dynamic calculation method. And it has a stronger theory basis and a higher accuracy than the static calculation method that uses rainfall times area.