Research On Ecological Detention And Flood Prevention In Hilly Areas Of Chongqing

Hilly areas are an important part of our country.Flood disasters caused by heavy rainfall are a serious problem that these areas generally face.Compared with plain areas,suitable construction land in hilly areas are scattered and limited.Besides,the population is concentrated in fragments,and the population density in each fragment is relatively high.With the same level of damage,the number of people affected is greater and the losses caused are greater.Therefore,more attention should be paid to flood prevention in hilly areas.However,traditional municipal infrastructure usually only has a single function such as flood prevention and drainage,rapid drainage,etc.,and its scale and renewal speed cannot meet the needs of the region,and it is no longer sufficient to deal with meteorological disasters such as heavy rains and floods.Therefore,in the context of vigorously promoting new rain and flood management facilities in recent years,this paper takes the hilly area of Chongqing as the background,and proposes to use ecological detention pond to detain the flood water in the area.Besides,this paper optimizes the filling of the detention pond based on the background of agricultural waste reuse,which is of great significance for the prevention and control of regional floods.The specific research contents are as follows:(1)The rainwater detention performance of the purple soil at 24 sampling points from 8 representative sites in Beibei District of Chongqing was studied.The results showed that more than 95% of the sampling points had a bulk density higher than1.35g/cm~3,with a maximum of 1.71g/cm~3,indicating that most of the sampling areas have been severely disturbed by humans,resulting in soil compaction and poor water permeability;the total porosity is between 35.99% and 51.33%,and the overall condition is good,the size of total porosity is related to the amount of soil water storage,and a few areas with a total porosity of less than 40% need to be focused on;the permeability coefficient is different greatly.If the flood prevention standards need to be met,the soil needs to be improved or ecological storage facilities need to be built in the soil to improve its storage performance.(2)Through constant head permeability test,the rainwater detention performance of biochar(fruit charcoal,rice husk charcoal,and pine charcoal)fired from three agricultural wastes was studied,and the effect of biochar on rainwater detention performance of purple soil was analyzed.The results show that the rain detention performance of different kinds of biochar is quite different,and the impact on the rain detention performance of purple soil is also different.Among them,rice husk charcoal has the best performance.In addition to its own good rainwater detention performance,it also has a significant improvement effect on the rainwater detention performance of purple soil.When rice husk charcoal is used as the ecological storage tank filler,it can accumulate 42.4% more rainwater than soil under the same conditions,which greatly improves the water storage capacity of purple soil;in the case of the maximum daily rainfall in the past ten years,it only takes 4min16 s for all rainwater to penetrate into the biochar,and it takes 11 h to penetrate into the purple soil,indicating that the biochar effectively increases the retention capacity of the purple soil.(3)This paper takes a small area in the hilly areas of Chongqing as an example for flood prevention research.According to the topography and height difference,the area is divided into 3 catchment areas,and the ecological detention ponds are dispersedly arranged to intercept and detain the 2892.84m~3 flood water generated in this area under the maximum daily rainfall in the past ten years.The total volume of the detention pond is calculated to be 2683.17m~3,but it is not enough for the flood water generated in the detention area.The volume of the detention pond needs to be corrected.On the basis of expanding the volume of the bottom detention tank,the volumes of the three detention ponds are 819.29m~3,1024.11m~3,and 1049.44m~3 respectively.According to the flood prevention standard of the study area,1.2 is taken as the safety factor,and the final volumes of the three detention ponds are 983.15m~3,1228.93m~3,and 1259.33m~3 respectively.