Passage of flood waves induces hydraulic forces and riverbed instabilities through which aggradation-degradation phenomena, originated by sediment transport, are expected. This mechanism is of paramount importance from the viewpoint of engineering aspects, especially in the field of river training techniques. It is well known that bed variation at river domain is the main cause of morphological changes, which in turn effects stability of hydraulic structures, as bridges, barrages, dams, revetments, dikes and many other river training schemes. For this reason there has been prolonged struggles in order to simulate impacts of flood wave passages with especial attention to riverbed variation forecasting, using mathematically based computer models. In this study Hec-6 model was used to predict the amount of bed variation of Qomroud River for floods of 2 to 1,000 yr. recurrence intervals. The span of study reach is in the order of 90 km with 15th Khordad Dam at upstream and the holy city of Qom at downstream. This study reveals that hydraulic properties of floods, especially water surface profiles, are effectively influenced from river bed variation, as they have distinct differences compared with solid bed case assumption. The range of influence varies form 5 to 40 percent in this specific case. Further more it is deduced that, depending on flood severity, state of dominant aggradation or general scour may be expected. Practical use of such models to determine zones of scouring and deposition is also another feature of this case study.
展开▼
