浸水被害軽減のための2方向接合円形落差マンホール部の構造改善に関する研究

抄録

The authors previously proposed a new model for manhole base shape with the invert located on the side wall of a manhole with right-angle pipes to reduce energy losses (1999). However, the alignment of connecting pipes in this model is different from the conventional position. For a new manhole model with a flat guide cover on the invert for a coventional manhole with right-angle pipes, the energy loss coefficient K (the total head loss/velocity head) is by about 0.6 to 1.3 smaller than the values of the conventional manhole type used in Japan. However, when rainfall in an urban area significantly exceeds the design value for rainfall on the storm sewer network, flood damage is unavoidable even if the energy losses at manholes in the area have been reduced. Recent changes in local rainfall patterns in Japan have caused frequent deluges that saturate the ground surface resulting in sever flood damage in low-lying areas. It might be possible to reduce flood damage in these areas by increasing energy losses at manholes upstream, and the intentional overflow from these manholes may delay the spread of flow over the ground surface downstream. When four kinds of baffle plate are installed in manhole outlets in straight pipes in order to reduce the cross-sectional area of flow to the downstream pipe, the energy loss coefficient K is by about 0.1 to 4.4 larger than the values of a conventional manhole type.