Abstract
As we have constructed closed type of sediment control dams in devastated watershed, sediment trap capacity of the dam has been decreased in a short period. It is necessary to think out efficient methods to increase a function of sediment control dam and groundsel. The sediment control dam with sediment control trap gate has been planned in upper reaches of Koshibu River. In this study, a slit was cut in Ogawara groundsel and effects of sediment control of slit type dam were investigated by the variation of channel bed survey, to examine sediment outflow from sediment trap gate. Furthermore, relationship between scale of runoff and sediment outflow from slit was discussed. As the result of this investigation, it was confirmed that effects on sediment control of groundsel increased by providing a slit of width of a few 3m for overflow section of width more than 100m.
