Research On Technology And Strategy Of Urban Stormwater Management System Based On Multi-objective

Compared with developed countries, policies, standards of urban flood control and rainwater reuse in our country has become increasingly complete, but stll lack systematic theory, standards, target system and technology system based on the rainfall runoff volume capture (volume and pollutants), according to China’s national conditions, study on urban muti-objective stormwater management system establishment strategy, method for determining the control target, planning control targets, planning and design methods is very significative for establishment of our country’s modern stormwater management system.Based on the research results of the domestic and international, urban stormwater management systems of developed countries, construction strategy for multi-objective stormwater management system, technology for stormwater management system based on rainfall runoff volume capture, urban runoff pollution and CSO pollution control technology, planning strategy and design method based on multi-objective stormwater management system were studied.The main conclusions are as follows:(1) In order to achieve the rainfall runoff volume, peak flow and runoff pollution control targets, China’s modern urban stormwater management system should include low impact development stormwater system, stormwater drainage system and runoff detention, retention and discharge system for extreme storm rainfall events,multi-scale construction from city, watershed to land, multi-level management from source reduction, midway transfusion and end of pipe detention and retention.(2) Rainfall pattern and distribution of storm events were the important impact factor to capture ratio of rainfall volume,runoff volume and rainfall events. More annual extreme storm events, more difference between capture ratio of rainfall events and rainfall volume,for arid regions more small and medium rainfall, capture ratio of rainfall volume is greater than rainfall events.(3) The minimum rainfall event separation time is the important design parameter for volume control,has great impact on annual rainfall volume and CSO frequency. The minimum storm event separation time should be determined based on the drain time or hydraulic retention time, considering the design operating conditions of infiltration and detention facilities, a minimum rainfall event separation time of 12 hours and 24 hours is preferable.(4) Capture ratio of runoff and rainfall volume corresponding design rainfall depth has a numerical conversion with recurrence interval, take 1 hour rainfall depth as an example,for volume capture target, the corresponding recurrence interval is not generally great than 1 year.(5) Micro system can effectively improve the comprehensive design standard of minor system.Take Beijing as an example, annual rainfall volume capture ratio of 85% enabling the runoff coefficient less than 0.5 under the recurrence interval of 3 and 5.(6) To determine the annual rainfall volume capture ratio reasonably, capture runoff pollution control based on end of pipe water quality should consider urban runoff pollution characteristics,water quality purification ability of the technologies,and predevelopment runoff status. An annual rainfall volume capture ratio of 90% for EMCcoD=200mg/L,CCOD=200mg/L,φpre=0.3, β=70%.(7) Statistical analysis of observatory 73 years’ minute rainfall data from 1941 to 2013,with a minimum rainfall event separation time of 12 hours, obtained annual rainfall volume capture ratio as a function of annual mean CSO frequency is:y=23.279e-0.097x (R2= 0.9945)(8) Total mainland runoff control rate target is divided into five areas, namely:I region (85%≤α≤90%),Ⅱ region (80%≤α≤85%), in region (75%≤α≤<85%), IV region (70% <a<85%), V region (60%≤α≤85%), the regional control rate of annual rainfall can refer the minimum and maximum limits given in the development of the total runoff the amount of control objectives.