Abstract
The amount of algal organic load in the stream assumed with length of 1.5 km, width of 20 m, and slope of 1/300 on the study site (Nagata) in the Tama River, was simulated by using expressions of change in algal biomass during biofilm development, and the correlation between the percent tearing-off of algal community and their biomass. It was conducted under three conditions of stone size distribution (stable area: 100%, 0%, 72% in Nagata) and several conditions flood frequency. When flood frequency is low and/or when the stability of streambed is high, the amount of algal organic load for down reach in the stream is estimated significantly high.