2　Study Area

As shown in Figure 1,the Diaocha Lake area is located in the northeast of the Jianghan Plain with the Hanbei River in the northeast,and the Han River in the south and the Tianmen flood control sluice in the west.The total drainage area is 1936km2,among which Tianmen is 919km2,Hanchuan is 984km2 and Yingcheng is 33km2.The terrain of this region is relatively flat,little tilted from northwest to southeast.Most of the ground elevation is of 24.0～28.0m in Tianmen and most of the ground elevation is of 23.0～26.0m in Hanchuan.

The drainage system of Diaocha Lake area is mainly composed of intersecting artificial ditches around the storage area and the spare storage area.The storage area and the spare storage area,known as the Diaocha Lake,is divided by separation levee and the spare storage area is located in the east.The area of storage area and spare storage area is 48.7km2 and 38km2 respectively.

The study area is crisscrossed by rivers and artificial canals,ditches.The main drainage canals are mainly composed of the east-west canals and the north-south canals with double dikes.The former includes the Xiatianmen river,the Nanzhi river,the Beizhi river,the south canal,the north canal,the Minle canal,the pump station river,and the latter includes the Fenshui canal,the east canal,the west canal.In addition to the above-mentioned river or canal,there are four branch with total area more than 150km2,respectively,Yangjiaxin ditch,Longzui ditch,Huayan Lake drainage canal,Nan Yu canal.

The study area is dotted with sluices and pump stations.There are more than 30 first-level sluices in the Diaocha Lake area,among which the Minle sluice,the Hanchuan sluice and that the Hanchuan pumping station sluice is the three main first-level sluice with a total design flow of 900m3/s.The total installed capacity of the 29 first-level pump stations is 46400kW,with a total design flow of 516.59m3/s,in which 12 first-level pump stations discharge into the Han River with a total flow of 420.89m3/s,and the others discharge into the Hanbei River with a total flow of 95.7m3/s.The 1st and the 2nd Hanchuan station and the Fenshui pump station is the three main drainage station under jurisdiction of Hanchuan Water Resources Bureau and the others belong to the village with limited drainage area.

There are 129 second-level sluices in the Diaocha Lake area,most of the control area is limited.The north floodgate on the north canal and the south floodgate on the south canal is the main sluice,which discharge water into the storage area when the water level of the canal is higher than 25.3m.The east floodgate on the east canal is the main sluice,which discharge water into the spare storage area when the water level of the canal is higher than 26.0m.The Hukou sluice at the intersection of the south canal and the Fenshui canal can adjust water between the Fenshui pump station and the Hanchuan one-station or the Hanchuan two-station.There are 102 second-level pump stations dotted along the main canal with the total design flow of 236.16m3/s,and the total installed capacity is 21857kW.