Effect of Cascade Reservoirs on Flood Routing in the Hongshui River, Southern China

Hongshui River, with a length of 659 km and drainage area of 130,870 km(2), is the upstream reach of Xijiang River, which is the dominant branch river of the Pearl River system in Southern China. There are 9 dams with a total storage capacity of 384.9x10(8) m(3) constructed on the Hongshui River and its upstream reach Nanpan River since 1980s (the annual water discharge of Hongshui River is 696x10(8) m3). The water level of the 9 reservoirs is connected together, which causes the riverbed channelizing and the flood characteristic changing during the processes of flood routing. To study the effect of the cascade reservoirs on flood routing, 363 flood peaks data of two hydrologic stations on the Hongshui River during 1971 - 2007 are collected to analyze the flood characteristics changing before or after construction of the large dam Yantan. The flood peak travel time is the main factor which is taken into consideration in this study. Statistics results show: (1) The flood peak travel time which varies with flood magnitude shows different trends before and after construction of the Yantan dam; (2) the average flood peak travel time with a smaller flood magnitude (< Q(P=50%)) is shorter in the post-Yantan dam period than in the pre-Yantan dam period. However, the flood peak travel time with a relatively larger flood magnitude (> Q(P=50%)) has no obvious differences before and after the construction of Yantan dam.