Abstract
One of the problems in flood control is the backwater in upstream direction which occurs when the river channel suddenly contracts. It is very important to understand the water surface profile in such river channels under the maximum possible flow considered the effect of climate change. In the present study, the following two works had been accomplished: 1, Using numerical simulation technics to quantitatively evaluate the water surface profile in river channel which including sudden contraction. 2, Using Yamada's theory to study the backwater-curve transitions considering the changing of cross-section area of the river channel. An example of the result of the present study indicates that a discontinuous water surface profile is formed at the contraction part of the channel. The flow at the downstream side of the contraction part is supercritical flow and the water level at the upstream side has been dam-up about 3m. The regime diagram of the water surface profile in the river channel which has sudden contraction suggested by Yamada showed that the result of numerical simulation agrees with this regime diagram very well. In addition, the storage effect of the unsteady and non-uniform flow caused by the non-uniformity of the river channel had also been studied. Using numerical simulation, we can calculate that how much quantity had been stored in the dam-up part at the upstream side and evaluate the effect of lowering the water level at downstream side.
