The reservoir storage loss caused by sedimentation is critical problem for those reservoirs which are expected to provide water resources and flood control. Hence, it is getting more important to promote sustainable sedimentation management in the near future. In this paper, RESCON model developed by the World Bank is introduced and the technical feasibility assessment of flushing used in the model is studied in order to apply it to reservoirs in Japan. After this assessment applying to several reservoirs in Japan, it is discussed that what is the points for successful flushing.

View full abstract

Vertical two-dimensional numerical simulation model is used to predict water temperature and water quality of reservoirs. There are many different models proposed. Those models can be classified according to their characteristics, such as basic equations, eddy viscosity coefficient modeling, numerical scheme and so on. However, the effect of the model level on the calculation result for reservoir flow is not clear sufficiently. In this study, we made vertical two-dimensional model dealing with flow, water temperature and SS concentration, and carried out calculations of typical flows in the hypothetical reservoir under the condition of various model levels, paying attention to eddy viscosity coefficient modeling and pressure modeling. As a result, by comparing the calculation results, the eddy viscosity coefficient modeling has a relatively significant effect on the results. On the contrary, the difference by pressure modeling is not remarkable.

View full abstract

In response to the frequent occurrence of large earthquakes in Japan such as the 1995 Hyogoken-Nambu earthquake, it is necessary to establish a safety evaluation method for dams during large earthquakes such as “Level 2 earthquake.” Embankment dams are supposed to settle due to the strong earthquake motion. We should, therefore, evaluate the earthquake-resistance of embankment dams by confirming that the catastrophic failure due to the overtopping of reservoir water does not occur. In this paper, we adopted the sliding deformation evaluation method by combining the dynamic analysis based on both equivalent linearization method and Newmark method, and analyzed the effects on sliding deformation of rockfill dams with a central earth core due to large earthquakes, considering strength of earthquake motion, up- and down-stream slope of dam body, reservoir water level and vertical earthquake motion. These results are very essential to establish a safety evaluation method for embankment dams during large earthquakes.

View full abstract

Recently in Japan, the number of the completed dams is getting more and more, but the cost for the management and the operation of completed dams should be reduced. Therefore, the rationalization of the instrumentation for dams is strongly required. In this study, we measured the exterior deformation of an existing rockfill dams with a central earth core using the global positioning system (GPS) as well as the conventional surveying methods, in order to investigate the applicability of the GPS to the measurement of the exterior deformation of embankment dams. Based on the results of case study, we concluded that the GPS could be applied to the exterior deformation of embankment dams.

View full abstract

When water is flowing from the bottom of a shell-type fixed wheel gate with a skin plate at the downstream side, the combined force is derived by the bottom pressure on leaf and by the weight of water in leaf and becomes extremely large downward force or uplift force. Because there is a huge water chamber in the gate leaf and water is filled in this chamber in closing condition and this chamber becomes vacancy when gate is fully opening. And under the operating conditions, water flows out from this chamber at the gate is opening and flows in at the gate is closing. There must be the suitable condition for the combined force between the parameters as the pressure at gate bottom, operating speed of gate, volume of chamber and both location and total area of holes for the water flows in and out. If this suitable condition is not satisfied under gate operation, the large downward force or uplift force arises. The method to derive the hydrodynamic vertical force is proposed in this paper on two types of gates such as the shell-type fixed wheel gate and the lower leaf of double leaf fixed wheel gate. And the effects of both the location and the total area of the holes, which are provided at the gate bottom leaf, are shown as the relation of hydrodynamic down pull or uplift force by numerical analyses.

View full abstract