Survival Time Span of Deposits and Characteristics of Bed Load Movement in the Torrential River Basin

Abstract

By estimating the age of deposits with the instrument of the ages of trees which stand on the deposits are by measuring the yearly quantities of deposits, the auther studied the life of deposits and the characteristics of bed load movement, deposition and removement.
The results are as follows ;
(1) In conformity with destribution of ages of deposits the channel can be divided into two characteristics zones, deposition zone and transportation zone.
(2) The survival time span of deposits, that is the time span which the deposits have remainedd unmoved in situ, is estimated by the age of the daposits. This survival time span corresponds to the difficulty of bed load removement.
(3) The deposit survival time span in years T is related to the accumulaled quantity, per 1km, of deposits through T, Q^T_a/l and is expressed as
log(Q^T_a/l)=α log T+β
The coefficient α is thought as an index which stand for the stage of desolation.
(4) The ratio of accumulated quantity of 100 years Q¹⁰⁰_a to that of 1 year Q¹_a represents the degree of basin desolation : the smaller Q¹⁰⁰_a/Q¹_a the greater is the degree of basin desolation.
(5) Values α, β and Q¹⁰⁰_a/Q¹_a are considered to be effective indice for comparing different basins in their characteristics in bed load movement as well as for planning sabo-projects.