Understanding linkage between channel process along a river course and hill-slope process with lateral sediment sources can be significant for management of sedimentary systems. The linkage that is characterized by distribution of storminduced sediment in a river channel is often expressed as sediment pulse (wave). This paper examines the propagation of sediment pulse formed by storm-induced sediment flow in two river channels of Southern Hokkaido, and classifies the patterns of sediment pulse based on difference in the distribution of accumulated sediment volume. Longitudinal changes in sediment volume along a river channel were modified to a sediment mass curve. Auto-correlation and crosscorrelation analyses were employed for examining sediment mass curves. The sediment pulses demonstrated with sediment mass curve was classified to four patterns, such as decreasing, increasing, intermediate and periodic types. Decreasing type along a transport-limited channel and increasing type along a supply-limited channel were dominated. Periodic type was not influenced by sedimentary link between channel and hill-slope but independently occurred by available sediment along a channel. Furthermore these types of sediment pulse were resulted to be influenced by channel width, channel slope and (quasi-) stream power. Although the highest peak of sediment pulse has been demonstrated at the channel reach with wide section and/or gentle slope, it has shown dispersed and lower peak at the channel reach with larger stream power.
A large-scale sediment-related disaster was occurred in the Hime River drainage area in July, 1995. To understand the timing of this sediment movement, the hearing to the person in charge of the local disaster prevention was investigated. As a result, it was occurred the timing of the sediment yield had concentrated around 18 o'clock July 11 in each tributary. But only Nakaya River was occurred the sediment yield in the early morning, July 12. Moreover, the scouring Tsukitsuki gate at the main river was 16 : 00-17 : 00 of the 11 th before the sediment yield of each tributary concentrated, the cause of damage to the building in the vicinity at Hime River spa is due to the sedimentation, and no water discharge increase. The reproduction calculation considered the timing of sediment yield. As a result, the streambed from the No.8 Shita-himekawa bridge point to Ohdokoro River rose in the maximum by about 10 m, and was corresponding to an almost actual phenomenon. As for the variation of riverbed, it has been understood that not only the sediment discharge but also the timing of the sediment yield is greatly related from the tributary.
2D numerical model of mudflows has been developed considering the estimation of sediment deposition in volcanic basins. Equations of erosion/deposition rate of suspended sediment were used in the 2D numerical mudflow model developed by Miyazawa et al. (2002). The previous mudflow model is improved in the present study by using the equations of erosion/deposition rate applicable to mudflow, which were determined empirically by laboratory tests from Hirano et al. (1997), Egashira et al. (1993) and Winterwerp et al. (1990). The erosion/deposition rates are related with the hindered settling velocity. The revised model was applied to compute the bed elevation variations inside Mega-Dike system in the lower Pasig-Potorero River basin near the Mt. Pinatubo, Philippines. It is found that the simulated bed variations are in reasonable agreement with the measurements. Using the model, the deposition areas of sediment to the several scale flood determined virtually are calculated numerically and estimated in the Pasig-Potrero River basin.
Sediment transportation from a forested watershed (88.6 ha) underlain by weathered granite was observed in a reservoir at the outlet of the watershed from September 2001 to October 2004. Wash load concentration was observed at the reservoir exit by manual sampling over 1 week, including a flood in October 2004. Bed load and suspended load comprising total load, i.e. bed material load excluding wash load, were calculated with hydrograph and sediment rating curve using the Einstein equation based on the hydraulic parameters of a study channel. Applicability of the Ashida & Michiue equation, and the Brown equation was also examined. Goodness of fit for the Einstein equation was the most satisfactory of the methods we examined because of the closeness of its total load estimation to that observed (3.67 ton/ ha/year) over the study period as a whole. However, even the best-fit model showed an underestimation during the earlier period. An overestimation of total load during the latter period implied a supply limit in the watershed. The early underestimation occurred under adequate sediment supply conditions following a large flood and the later overestimation was attributed to a rapid stabilization of unstable sediment sources. The proportion of bed load to total load was estimated by the model at 79% and suspended load at 21% ; wash load proportion to observed total load was 11 %. These results showed that the proportion of suspended load was at the same level as the value quoted in other reports from Japan but wash load was not so small as that. Grain size distribution was coarse (2.2 mm in D50) and uniform. The smaller total load can be attributed partly to the uniformity of grain size from weathered granite in comparison with bigger total load caused by the wider range grain size distribution assumed in the model, and partly to the fact that the watershed was well managed and covered by dense forest.
Iide Sankei Sabo Work Office has been advanced to provide slit in existing sabo dams so that to improve the sediment control function and consideration of river environment (water quality improvement, to allow passing of fish). However, the effect of a series of slit sabo dams is not clear, though some researches exist. The purpose of this research is to get the supporting data for the decision of basic policy to provide slit in existing sabo dams at jurisdiction basin in the future by examining the effect of a series of slit sabo dams with one-dimensional river bed simulation on a model river basin Kaminosawa.
Boulder distribution is an indicator of the physical and environmental condition of a river in a mountainous area. This research aims to understand the natural distribution of boulders on a riverbed in a mountainous area. Continuous survey was made of long section of river using debris indexes. Boulder distribution was clarified in natural river sections and in artificial river sections installed with erosion and sediment control structures. It was found that the distribution of boulders near erosion and sediment control structures is not natural, and that the distribution differs according to the structure. Data on boulder distribution in river sections in mountainous areas can serve as fundamental information for environmentally friendly sediment control projects whose aim is to preserve and/or restore the natural environment of rivers in mountainous areas.