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    Brief Introduction to the Flood Control Work in the Taihu Basin


    I. Basic water and rainfall information in the Taihu Basin

      The Taihu Basin belongs to a subtropical monsoon climate zone. There are four distinctive seasons, abundant rainfall and adequate heat here. In winter, the invasion of continental cold air mass brings about prevailing north wind prevails, and the climate is cold and dry. In summer, controlled by marine air mass, southeast wind prevails and the climate is hot and wet.

      The average temperature over years in the Taihu Basin is 15-17℃, featuring higher temperature in the south and lower in the north. The average rainfall whose spatial distribution gradually decreases from southwest to northeast is 1177㎜ over years. Inter-annual variability of precipitation changes significantly and the distribution of yearly rainfall is uneven, influenced by the changes in monsoon strength.

      There are three distinct rainy seasons annually in the Taihu Basin. Spring rain, from March to May, features many rainy days that account for about 30% of the annual rainy days. The Meiyu period, from June to July, features abundant rainfall, accounting for about 20%-30% of the annual precipitation. The Meiyu period usually lasts 23 days, there are greater changes in number of days and precipitation. For example, the Meiyu period lasted only 3 days and the precipitation was 48㎜ in 1958, whereas in 1954, the Meiyu period lasted 59 days and the precipitation was 400㎜, which was 9.6 times that of 1958. During the Meiyu period which ranges long spell land large area, the total amount of precipitation is large, thus it may result in increased likelihood of basin-wide floods. Typhoon, with a comparatively shorter period from August to October, has greater precipitation intensity and often leads to serious regional floods, such as the Typhoon No. 6214 on the 5thof September in 1962, during which the precipitation of Suzhou 2 days reached 439㎜.

      The Meiyu period and typhoon rain are the main causes for the floods in the Taihu Basin.

    II. Governance of the Taihu Basin Project

      The Taihu Basin witnessed big basin-wide floods in 1931, 1954, 1991 and 1999. With the rapid development and high centralization of the economy and society, the consequence financial loss continued to increase.

      In accordance with the planning of water conservancy in the basin, the first round of comprehensive regulation began in 1991. Altogether 11 key projects have been built in the basin, i.e., Wangyu River, Taipu River, Hang-Jia-Hu South Discharge, Hang-Jia-Hu North Exhaust Passage, Lake Levee, West Cited Discharge, Red Flag Pond, Tiaoxi Flood Protection in East and West, Expanding the Highway of River Port and Xietang, Wuchengxi Cited Discharge, Huangpu River Upstream Flood Control. Combined with the existing water projects in the basin, the Taihu Basin has initially formed a project system through which the flood flows northwards into the Yangtze River, eastwards into the Huangpu River and southwards into the Hangzhou Bay. The system makes full use of the regulation and storage in Taihu --- storage and discharge coordinated, but the main purpose is to discharge. In addition, the whole system has initially had some basic conditions, such as flood control, optimal allocation of water resources, and reasonable dispatch.

      On the basis of Comprehensive Planning for Flood Control in the the Taihu Basin and the integrated regulation of water environment program, such subsequent projects are to be implemented in the Taihu Basin as subsequent Project Around the Lake Levee, subsequent Project in Wangyu River, subsequent Project in Taipu River, Extension Project in Xinmeng River, Dredging Project in the East of Taihu and Flood Discharge Project in Wusong River, Expanding Project of South Discharge in Hang-Jia-Hu District, Extension Project in Xingou River, subsequent Project of Flood Control in the East and West of Tiaoxi, Sluice Project in the Estuary of Huangpu River etc.. On completion, all the projects are to be combined with regional key projects and urban flood control projects to further enhance flood control capacity in the Taihu Basin.

    III. The main problems of flood control in the basin

      At present, the problems of flood control work in the Taihu Basin mainly lie in four aspects. First, the overall flood control standard in the basin is low, which is incompatible with regional economic and social development. Second, the capacity of flood discharge in the basin is insufficient and the conflict between flood control and flood discharge is serious, which lead to increased difficulty of coordination between basin and region, and between flood control and water supply. Third, there exist vulnerable spots in the key flood control projects, which affect their overall functioning. Fourth, underlying surface in the basin has undergone great change, which makes the flood control and disaster reduction more difficult.