numerical analysis of hydraulic performance of negative surge on earth dam discharge

A negative surge is an unsteady flow characterised by a decrease in water depth. negative surges can occur downstream of a control structure when the discharge is reduced. they also occur upstream of a control structure that is opened rapidly or the failure time is very low. for a stationary observer the negative surge appears to be a gentle lowering of the free surface. the hec-ras model based on the linearized implicit finite-difference model which based on the de st. venant equations. the various implicit methods of finite differences that have been developed, the preissmann-type schemes. when the surge occurs, the de st. venant differential equations are not valid in the neighborhood of the surge. in this case was used software fortran 90 and write code to solve the explicit mccormack model. according to this paper provides the parametric models methods and numerical model such as maccormack explicit scheme and preissmann implicit scheme using hec-ras to simulate dam break furthermore it used to predict breach outflow hydrographs .unsteady flow modeling is often used in dam breach analysis due to the need to obtain more detailed or accurate results. the breach parameters will directly and substantially affect the estimate of the flows. due to this illustrate the failure time is very low, as a result the negative surge occurs, however de st. venant differential equations are not valid in the neighborhood of the surge. in order to evaluate the effective of negative wave on the outflow hydrograph. according to this, the outflow computed by the simplified model with the explicit method of characteristics maccormack.