Numerical Modeling of the Effect produced by repeated floods and estimation of the risk zones

Abstract

In Romania, in the last decades, any plan of management concerning the environmental rehabilitation of the natural riverbeds has not been made. After the floods from 2004, 2005 and 2014 uncontrolled deposits of sediments have been recorded or, in contrary, in other places zones with erosion and uncontrolled coastal slides. As an immediate effect zones with risk for the local population, and not only, have appeared. The present paper estimates the capacity of transport of riverbeds in real conditions, based on local measurements registered during and after the floods. The model is tested for the Bistrita River, an area well-known for repeated floods, sometimes even in the same year. Near the watercourse, there are many locations, with a high population. The time variation of the liquid and solid phases discharged are directly connected with the sediment transport. In these conditions, the fine fractions from the material of the bed sediments are removed from its surface. Some of them become armored with the coarser part of the bed sediment. It is proposed a mathematical model to simulate the effect of both types of deposits, to study the surface of an open channel, with a movable bed. The entire alluvial stream, until the base rock, is considered with a small thickness so the non-uniformity of the grain size in vertical distribution from riverbed could be neglected. The boundary conditions in flood analysis consist in the upstream hydrograph and the stationary downstream water level. Knowing the flow rate and the water levels by direct measurements, there is possible to establish the risks zones, far away from the river borders. The primary purpose of this study is to minimize the effects of such uncontrolled floods, to detemine the risk zones and to present a solution for increasing the safety near the riverbed. Finally, some conclusion and references are mentioned.