STUDY ON EFFECT OF SEDIMENT SUPPLY CONDITIONS ON POROSITY AND GRAIN SIZE CHANGES OF RIVER BED
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Sediment production rate in a volcanic basin is not constant, and it depends on the volcanic eruptions. The sediment production often gives problems, so that the sediment should be managed. Effect of sediment management is changes in qualitative and quantitative of the sediment. Effect of sediment management on sediment changes qualitatively is often studied, but study on qualitative sediment changes is still few. Therefore, influences of human activity and natural condition on changes in sediment qualitatively are needed to be studied. This study is conducted by experimental and numerical methods. porosity and grain size are used as parameter to describe sediment quality. Numerical method uses One Dimensional Bed porosity Variation Model. This research is conducted using three cases. Case 1 is without sediment supply, Case 2 is with log normal distribution sediment supply, and Case 3 is with uniform distribution sediment supply. Based on the result, Case 1 shows that river bed becomes croarser and the porosity tends to increase due to no sediment supply from upstream cause by natural process or human activity. The grain size distribution changes from long normal type to Talbot type. In Case 2, if there is sediment supply from upstream due to an eruption, the river bed elevation increases. Grain size distribution changes from Talbot type to lognormal type and the porosity decreases. In Case 3, grain size distribution changes from lognormal type to uniform and the porosity increases. The comparison between porosity and grain size changes in the experimental and the numerical result has shown in a good agreement.