This paper aims to clear the movement about the sediments (boulder, cobble, gravel and sand), which fall down the downstream edge of the Sabo-dam, and so that, we can decide reasonablly to make the planning of its downstream slope. In that case, we examined the trace marks impacted by falling sediments on such a place as already builted the Sabo-dams front apron and velocity of sediments on various conditions. The results show as follows: 1) The trace marks of the Sabo-dam's concrete front apron are grouped into three types on the plane figure (Fig. 3) and the fives on the vertical section (Fig. 5). 2) When the sediments fall down from the downstream edge of the Sabo-dam, those velocity change remarkablly, especially, the large stone (boulder, cobble, gravel) generally fall down inside of the rear nappe, but the more the amount of flow greater, the more it likely to show the sight of “within the nappe” or “along with the rear nappe”. The movement of the sediments, above mentioned, is quite similar to the one of singles. 3) The distribution forms on the falling sediments are quite similar to the one of the trace marks of the Sabo-dam's concrete front apron. 4) From the ovservations of the falling sediments trace caused by the flood, the sediments which flow down within the nappe or along with the rear nappe, are estimated about 60-70% of total amount. 5) In the case of the flood, when the streaming sediments fall down from the downstream edge of the Sabo-dam, the amount of sediments which are smaller than the average grain diameter are falling down within the nappe or along the rear nappe. 6) In the case of the flood, the bed-flow velocity which often show including the amount sediments in the stream is estimated by an extant 70-90% of the surface velocity.
It is well-known that there is a close relation between the chemical compositions of waters and weathering of rocks as one of indices to predict the landslide. The purpose of the study was to examine the relationship between landslide and weathering condition in stream basins regarding water quality. Water samples of ordinary water and flood waters have been collected twice from the 27 valleys in the Yoshino river basin, fractured zone, Shikoku. The authors have examined the relationships among the chemical species contents of waters. In this report, qualitative properties of water in the fractured zone was clarified. Cations biocarbonate ions which had relations closely with the weathering were also explained. Finally the relation between the types of landslide and water quality was discussed.
When we dispose Sabo-works rationally, it is necessary to study the function of Sabo-work quantitatively. In this paper, the author tried to numeriae the diffusing function of cross-dyke. 1) The author considered that the degree of cross undulation in a stream bed became an index of bed load's concentration. 2) The degree of cross undulation was presented as a numerical value by making use of standard deviation. And this numerical value divided by the cross Breadth was named as Degree of cross undulation (D.u. in short). 3) Degree of bed load's concentration (D.c. in short) in arbitrary length of Channel was exhibited as the average of D.u. 4) By surveying Channel work in field, it was confirmed that the bed load in narrow interval of cross-dyke dispersed broader than in wide one. 5) The model experiment proved that the bed load dispersed broadly under narrow interval of cross-dyke. And in case of becoming gentle slope, the bed load dispersed more broadly. 6) Consequently it can be considered that D.c. is one of effective methods in case of estimating the diffusing function of cross-dyke.