Due to irrational exploitation of water reserves from some hydropower systems and due to improper maintenance of the natural river beds, in present days, in conditions of abundant rainfall, the whole area into river vicinity are in a real danger. The present paper is dedicated to estimate the real capacity of transport of natural riverbeds in permanent correspondence with the zone reality during and after repeated floods. A numerical model based on experimental measured local data is elaborated. In these conditions in 2005, 2010 and 2012 in the Siret basin, on Bistrita and Cracau rivers area, nine floods considered major were mentioned, followed by human victims, lost animals, and huge terrains under water for more than five weeks. First is presented an actual documentation concerning the situation of functioning, producing, transport and exploitation of hydro systems from the affected areas, based on local experimental measurements. A new numerical modeling of the free surface water flows is realized, taking into account the possibility of permanent changing of lateral surfaces (river beds) during floods, due erosion and sediment transport. It must be considered that during the floods may appear also zones with uncontrolled deposition of the moved and transported sediments. Finally, an optimum management of the flow rate on short and medium term, to assure the environmental protection of the affected areas and some conclusions are mentioned.
