A modified method of runoff analysis is proposed and examined to apply the long and shortterms runoff model (LST-II), which is developed by Kadoya and Nagai (1988) for analyzing both flood and long term runoff successively, to the distributed type of basin model. The outline is as follows:
The model incorporates two stages of runoff routing. In the first stage the rainwater flow on a hillslope area to become the lateral inflow hydrograph for the second or stream phase is evaluated by the modified LST-II model having the bottom width of equivarent to slope length for each slope system. The second stage is one for routing the stream hydrograph by a kinematic wave equation.
The stream system in watershed model is constructed on the network evaluated the sources of first stream order on map of a river basin with the scales of 1/25,000 or 1/10,000.
As the result of runoff analysis in the Hii River basin of 9ll.4 km2 and Otonashi reclamation area of 0.29km2 it is showed that the modified LST-II model can be possible to utilize the flash flood forecasting in the basin involved partial developed and/or urbanized area and apply to the runoff analysis considering for the characteristics of channel network and various land form in the basin. But, in details, it is pointed out that the model is possibility to underestimate the discharge at peak parts of flood hydrograph slightly.