The long-term growth, decay and disappearance processes of sand waves and the variations of sand waves resistances with bed variations of the Tone River mouth from 1961 to 2007 are clarified in this paper. At first, we examine characteristics of the arrangement of dunes which are seen in the downstream of the Choshi Ohashi Bridge. Next, the long-term growth, decay and disappearance processes of dunes are indicated by the variation of cross-sectional bed forms surveyed from 1961 to 2007. The variation of sand waves resistances and bed elevations during the floods in different years is evaluated by a numerical unsteady flood flow and bed variation analysis based on the observed temporal changes in water surface profiles. At last, the characteristics of the sand wave resistances in the Tone River mouth are clarified by comparing with the previous studies on sand wave resistances in alluvial rivers.

View full abstract

 The synthetic probability method is used to estimate a T-year flood peak discharge taking account of time and space distributions of rainfall, which is used for a river planning in some catchments in Japan. In this paper, a relationship between a distribution fuction of annual maximum rainfall and annual maximum flood peak discharge is newly developed under some assumptions; then the synthetic probability method is theoretically derived from the relationship.

View full abstract

 Energy loss at manholes under surcharged conditions is as important as the friction loss in pipes in the design of storm sewer networks and in flood-analysis. Some researchers have already proposed the formula to calculate the energy loss at three-way manhole under surcharged conditions. However, in most of these proposed formulas all variables of structural elements for the pipes and the manhole have not been considered enough yet. Therefore, development of the formula to exactly calculate the energy loss at three-way manhole is needed. In this paper, the effect of diameter ratios between inflow pipes and an outflow pipe, the ratios of flow rates between inflow pipes, connected angles among those pipes and drop gaps between inflow pipes and outflow pipe on the energy loss at three-way circular drop manholes were investigated. Based on the experimental results, a new formula was proposed for the energy loss coefficients at the manholes that considers all structural elements and the ratios of flow rates between inflow pipes. In the proposed formula, calculated energy loss coefficients reproduce measured values more exactly than existing formulas.

View full abstract