Assessment of potential rainwater use in urban areas of reception basins of South-to-North Water Diversion Project
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Abstract:
The extreme hydrological events such as storms and droughts are sharply increasing,which leads to the coexistence of urban floods and drought.Scientific control of urban rain and flood process is the frontier and hot spot of urban hydrology.Rainwater utilization is one of the important means to alleviate urban waterlogging,and also a key issue to determine the water diversion scale of the subsequent South-to-North Water Diversion Project (SNWDP).It is very necessary to assess the potential of urban rainwater use in the reception basins of SNWDP. The rainwater utilization levels of sponge pilot cities were investigated and analyzed,considering the geographical climate and precipitation characteristics in central-eastern and western China.The two different indicators "Proportion of Tap Water that replaced by rainwater water (PTW)",and "Proportion of Rain Water that used by human beings (PRW)" are used to quantify the rainwater water utilization levels in sponge cities.The conversion formula was put forward to unify the two indicators as PTW.Considering the economic and technical feasibility, the upper, lower threshold, and an average of PTW in the central-eastern and western regions were calculated.The uncertainty of urban rainwater utilization and the guaranteed rate of rainwater supply were quantified based on the hydrological frequency analysis method. The potential rainwater use was calculated based on the datasets of year 2018.The result is 620 million m3, 470 million m3 and 326 million m3 for high,medium and low utilization levels,respectively.Based on the hydrological series from 1970 to 2020,the potential utilization of rainwater resources is 466 million m3,389 million m3 and 282 million m3 for a normal year (P=50%),dry year (P=75%),and extreme dry year (P=95%),respectively.Taking Beijing,Tianjin,Shijiazhuang,Jinan,Taiyuan as sample cities,the guaranteed rate of rainwater utilization was obtained, which were 45.1%,51.0%,41.2%,45.1%,47.1%,respectively, with an average rate of 45.9%.The average rate is far lower than the requirement of the urban water supply guarantee rate. The potential urban rainwater use is quite small compared with the total demand capacity of subsequent projects of SNWDP.Due to the randomness of precipitation,the rainwater use has the characteristics of high uncertainty,low guarantee rate and great interannual variation.The rainwater is suitable as a supplementary water source for the city,instead of serving as a stable water supply.
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