Study On The Runoff Coefficient Of Mountain Urban Greenland And Cement Road

At present, the rainstorm, rapid formation of short, duration rainfall and localsudden intensity, cause the city waterlogging seriously,with the frequent occurrence ofextreme weather.Design lag is the main reason for urban waterlogging, runoffcoefficient is an important parameter for the stormwater design flow calculations.Nowrunoff coefficient values, in the design of rain system, mainly with reference to theprovisions of"Outdoor Drainage Design Code GB50014-2006",while the provisions ofthe runoff coefficient value，according to ground cover types which was determined inthe experience, and don’t take the ground slope, geomorphology and other factors intoconsideration.Therefore，the experiments carry out the study on the runoff coefficient ofa single urban underlying surface, selecting the green and cement road as the mainunderlying surface, combining with the major projects of national water pollutioncontrol and governance of science and technology, Chongqing City, the drainage systemsecurity and urban non-point source pollution control technology research anddemonstration topics.Selecting Chongqing as the representative, the experiments carryout the study on runoff coefficient of urban green space and cement road for the specialtopography of mountainous city, providing design parameters for the mountain urbandrainage network design and non-point source pollution control, providing theoreticalreference for the city waterlogging control theory research, planning, designing andengineering applications.Experiments,Shapingba District, Chongqing30years (1980-2009) rainfall data asbased, analysis rainfall characteristics of Chongqing City, determining the type ofsimulation of rainfall, rainfall and rainfall duration, peak, etc. At the same time,, itselects0°to5°,5°to20°from20°to45°as the green slope,0°to5°,5°to10°,10°~15°for road slope on analysis of Chongqing Green and road runoff coefficientfactors. Development of artificial rainfall model, we take85field simulated rainfall andwater balance accounting, analysis of slope, rainfall duration, peak rainfall intensityfactors on the process of green and cement road runoff coefficient by the experimentalresults.Available through experiments, runoff coefficient of green space and road have thesame point.Runoff coefficient, with slope, rainfall, is a linear relationship, increasingwith the increase of the slope, rainfall under the same rainfall patterns. The runoff coefficient, which increases gradually, extending with the rainfall duration andstabilized finally, is an exponential relationship with rainfall duration.The peak ofrainfall more later, the greater the runoff coefficient.The interaction of each factoranalysis, the most important factor of runoff coefficient are derived slope, followed byrainfall, rainfall rain peak position and duration of rainfall, while position of rain peakplay the role runoff coefficient of green stronger.Green spaces play a strong role in the retention of rainfall. The simulation test ofheavy rain does not produce runofff. Runoff coefficient of three different slope, from0°to5°,5°to20°,20°to45°, were0.08to0.20,0.09to0.26,0.12to0.42, the runofftime were30min to85min,30min to65minutes,30minto55min, the time of peak lag60min to105min,55min to85min,45to60min.Continuous production flow time isvery short, rarely continuous production flow after the rainfall stopped.The runoffcoefficient cement road, from0°to5°,5°to10°,10°to15°in three different slope,were0.97to0.98,0.92to0.97,0.92to0.98, the runoff timewere1min to5min, time ofpeak lag15min to20min, after the stop of the rainfall runoff time15min to20min,runoff coefficient of road increases with slope increasing, and finally,the stabilityof the flow tends to a constant0.98stable. Compared with the runoff coefficient of thestorm sewer design, Outdoor drainage design specifications GB50014-2006"in clause3.2.2provide the provisions of parks and green runoff coefficient between0.10and0.20,concrete or asphalt pavement runoff coefficient between0.85and0.95, runoffcoefficient of mountain of urban green space, road is relatively large.During projectdesigning, we should be adapted to local conditions, considering the runoff coefficientselection.