PROCESSES OF DEBRIS TRANSPORT IN MOUNTAIN WATERSHEDS AND DEVELOPMENT OF MOUNTAIN SLOPES AND VALLEYS

Abstract

A general form of the formulae for tractional load can be given in th formQB=cτα, where QB is the tractional load, the tractive force, a an exponent and c a constant. Most of the formulae for tractional load proposed thus far were obtained from the results of ex-periments carried in flumes with gentle gradients. The value of α which can describe the mechanism of debris transport in steep mountains was tried to obatin by comparison of measured amounts of erosion of actual mountains with calculated ones from Eq. (2). Eq. (2) which describes the changes of longitudinal profiles of average slope and valley bed was derived by using the above general form. High cor-relations are obtained when the value of α are 3 and 3.3 as shown in Table. 1. The value of α in Brown's equation is 2.5, and that in Sato, Kikukawa and Ashida's equation 1.5. As a result, it is confirmed that the basic processes of debris transport in the form of mass movement and by the action of running water in mountain watersheds with great gradients, can be approximated by the above general form. By using Eq. (4) of which α is 3.3 (m=2), topographic factors which reflect the rate of erosion of a mountain were studied, and the development of fault scarps and valley slopes were considered. Consequently, it is shown that the rate of erosion can be represented by a power function of mean slope of a mountain (Fig. 3). It is also shown that the average slopes of fault scarps which have been shaped by the interaction of uplift and erosion are straight, and the larger the rate of uplift is, the steeper the slope becomes (Fig. 5). From the laws of channel networks, it is derived that the longitudinal profile of the main valley of a basin which is in a steady state can be represented by a logarithmic curve. Profiles obtained from Eq. (4) and the longitudinal profiles of valleys which dissect fault scarps and volcanoes, can be represented by straight lines on semi-logarithmic paper when the locations of the divides are transferred horizontally.