We had many calamitous disasters in 1972, 1973 and we wil lhave disasters in future, because we live in very dangerous land. So it needs the Sabo works for the preventing the sand disaster but it's so many-that it cannot excute the Sabo works in anyplace at once. Then, we need the alarm system for preventing the sand disaster. I propose the one method of alarm system with rainfall intensity ratio which is called σ, in where σ=tanθ1/tanθ2=dm·dT/dM·dt in Fig2. As a result, I think σ is very useful factor for forecasting the sand disasters.
On predicting the sediment transport rate at reaches of a watershed, we cannot ignore what proceeding in the stream network according as the transport competence of reaches are exceeding or overloaded with debris available. To reveal the process, there is a need of statistical or stochastical treatment, as the conventional “ delivary ratio ” is too generalized and as the deterministic follow along the whole course are too complicated to camplete. A idea of statistical or stochastical procedures is proposed, and a usefull index of transport competences is composed of geomorphological measures.