Abstract
Some intermittent surges on instability are known as roll wave. Lots of intermittent surges of muddy debris flow had been observed at Hasegawa, Nojiri River and other rivers on the Sakurajima basin and other areas. We got a solution of first order approximation on wave length of roll wave based on a turbulent - particle collision flow model. This paper shows a theoretical wave length of roll wave of the flow with non-cohesive sediment, and discusses relationships of the results and some experimental results.