The Engineering Design And Benefit Analysis Of Roof Rainfall Recharge Karst Water

With the rapid development of urbanization, the area of grassland, bare land and cropsetc are gradually decreased; instead of a large quantity of sclerosis ground such as roads,buildings and so on. The enlargement of urban impervious area will increase the volume ofsurface runoff and cause greater pressure for flood discharge system on the one hand,consequently increased the risk of city flood; on the other hand directly reduced ground waterrecharge, a large number of rainwater flew away by drainage system, causing the waste ofwater resources.In the21century, the rapid development of industry and agriculture, improvement ofpeople’s living standard, a series of problems caused by urbanization especially the urbanwater resource crisis, has attracted the attention of many countries at home and abroad, whichhas became the bottleneck of restricting city economic and social sustainable development. Inaddition, the city water source only supplied by natural river water and ground water.Groundwater in many northern cities of China was over-exploited, causing many problems,for example, the shortage of groundwater resource, water level fell continually, landing funnel,and corresponding geological disasters such as ground subsidence, collapse and so on. Theylead to the damage of water environment which is closely linked to our life, and then alleviatethe contradiction between supply and demand of water resources is imminent. Therefore,make use of roof rainfall became the focus of domestic study and international studygradually, the scholars all around the world made a large number of study on the water qualityof roof runoff, the results showed that the roof runoff was slightly contaminated. It hasbecome a direction of water resources development and utilization, which has so muchpotential. Use rainwater to recharge groundwater has many benefits, not only rose ormaintained the water table, prevented and reduced the land subsidence, avoided sea water toflow backward on coastal areas, but also increased the available volume of groundwater, so asto achieve the sustainable use of water resources, taking account of the economic, social andenvironmental benefits.The pollutants of roof runoff majorly concentrate on the initial stage of rainfall; hence,the selective abandon of early roof rain runoff roof is the key to recharge groundwater artificially. Jinan has favorable hydro-geological conditions to carry out artificial recharge,namely fracture karts aquifer has a large permeability coefficient. Therefore, this paperstudied the characteristics of Jinan roof rain runoff, analysis the change trend of mainpollutants with the delay of rainfall, so as to determine the value of the early abandon flow,improved initial rain abandon flow device, completed the final design and construct of roofrainwater collection recharge engineering, which was operated in Aug.2011. Furthermore,analysis the engineering benefit, put forward management measures, provided basis for nextfurther study on groundwater recharge. Main achievements are:1. The main pollutants of Jinan roof rainwater runoff include F-, Cl-, NH3-N, NO2-, NO3-and turbidity, initial rain runoff pollutant concentration is higher, as the delay of rainfall,which has been the water scouring and pollutant concentration gradually reduced to a steadystate.2. Based on the study of the pollutants concentration of the roof rainfall runoff of Jinanduring two rainfall process of2010flood season, according to the graph of pollutantsconcentration and accumulative total rainfall, the early abandon flow was defined as6mm,considering the cost of rainwater collection system and the maximize recharge volume.3. Designed a suitable device of early rainfall abandon of rainwater collection injectionproject, which has applied in the recharge engineering.4. Designed and constructed the roof rainfall collection recharge engineering, the mainformation include early rainfall abandon device, regulation pond, filtration pond and rechargewell.5. Make a simple benefit analysis on roof rainwater recharge karsts water engineering.Although the economic benefits is not ideal, which will produce social and environmentalbenefits, so can make a great difference on water supply and spring spewing of Jinan.