## NUMERICAL SIMULATION OF FLOW AND MORPHOLOGICAL EVALUATIONS IN RIVERS UNDER DAM-BREAK FLOWS

M.D. Saikia and A.K. Sarma

### Keywords

Numerical modelling, simulation, dam-break ﬂow, riverbed, deformation of channel section

### Abstract

This paper presents a numerical model to simulate the unsteady water and riverbed proﬁle due to failure of a large dam in a natural river. The mathematical model is built upon the conservative laws of shallow water hydrodynamics. Over the recent decades, there have been continuing eﬀorts to understand dam-break hydraulics and the majority of the studies have been carried out in laboratories where channel bed is assumed to be ﬁxed under such a highly transient ﬂow. Dam-break hydraulics of natural rivers is indeed complicated, and involves not only water ﬂow, but also morphological changes in the riverbed, which in turn has modiﬁed the predicted ﬂow proﬁles. Although very few numerical models are proposed for mobile beds, applications were only in simple laboratory channels. The present investigation carried out in a Himalayan river clearly shows that the free surface proﬁles and hydrographs are greatly modiﬁed by natural riverbed mobility under high supercritical dam-break ﬂows, which is extremely signiﬁcant for ﬂood predictions. Again as the change in the topography is not conﬁned only to a rise (or a lowering) of the riverbed but also causes consequence in the form of a completely diﬀerent cross section. Hence in the model another new important point is included to get the ultimate cross-sections of the river channel after the dam-break ﬂood. The role of the form of the governing equations for developing suitable numerical simulation models for real-world complex conditions are also analysed. Numerical models applied earlier, providing comparable solutions, are referred as experimental and real dam break with small dam height is not found to be acceptable in case of large dam like Dibang failure conditions. To fulﬁl above, a simple, comprehensive model is proposed. The model is tried to be made detailed one with speciﬁc features such as consideration of the changes in riverbed elevations and frictions, channel cross sections, sediment entrainment, depositions across the bottom river channel, etc. These indeed are enhanced aspects of this study as compared to most of the past work available in literature where ﬁxed riverbed has been considered.