Research on disasters by floods and geomorphological changes

点击翻译按钮获取中文摘要

In order to conduct "research on disasters by flood and geomorphological changes", three sub-themes are prepared ;(1) Characteristics of rainfall and surface runoff,(2) Sediment runoff and river changes, and(3) Beach erosion.Discussions associated with topics (1) and (2) are made mainly on the problems in the Brantas river. The third topics is conducted with attention focused on the coral reef of Bali island as well as on the Semalan beach located on the north-central Jawa. In performing the study, data-analyzes, observations for data collections and numerical simulations are employed. Results are sammerized as follows :(1) A long and short terms rain fall runoff method its proposed in the upper Brantas, and is applicability is tested by using the runoff data at Karankates dam reservoir. Applying remote sensing images and a geographic information system, land cover classification and geomorphologic characteristics are realized. Rainfall runoff was computed by the kinematic wave method … More for the hillslopes and river channels, while sediment yields from tributaries was estimated by unit stream power method.(2) Numerical methods evaluating one dimensional river change as well as two dimensional one are developed, taking both contact loads and suspended sediment, and sediment supplies from tributaries into consideration. The methods predict longitudinal bed variation, local crosions forming concave river banks and propagation of bed material, and were applied to the Brantas to evaluate the river change. In addition, a method is proposed by means of a tidal reservoir for reducing the river mouth sedimentation. It emphasizes that optical operation of tidal reservoir prevents the river mouth from severe sedimentation.(3) A beach erosion method is developed, based on 2-D governing equations and data analyzes. It predicts wind-induced and wave-induced currents and beach crosion process. Numerical simulations have been conducted to predict the beach processes for cultivated coral reef as well as for rapid change of sediment supply due to shortcut of river course. Less