LONG-TERM TOPOGRAPHY CHANGE IN LOWER REACHES OF THE YOSHINO RIVER

Abstract

Topography change over a period of 34 years since 1967 is analyzed statistically with respect to the most downstream reach of the Yoshino River, in Shikoku. A linear trend method (LTM) and an empirical orthogonal function method (EOFM) are utilized. As a result of the LTM analysis, contrary tendencies of topography change, namely rapid degradation and gradual aggradation of riverbeds, are described in regard to the periods before and after 1985, respectively. It is found that by the EOFM analysis that the first-order and the second-order modes of topography change are closely related to gravel digging and dam construction, respectively. Short-term prediction of topography change in a reach within 5km from the river mouth is carried out by means of extrapolation of eigen functions obtained by the EOFM.