RADAR-BASED RAINFALL ESTIMATION IN BOYONG RIVER (BO-D5)

Sediment-related disasters are terrible disasters that can catastrophically impact facilities. People must keep in mind to make sediment-related disaster information that can be predicted from rainfall and response of drainage area by using snakelike. This research produces important indices on precipitation related to debris. It shows the current status of the stage of the response of drainage area against rainfall by using a couple of short- and long-term indices. It shows the water storage volume in the soil layer with the calculation of soil water index (SWI) by using X-band MP (Multi-Parameter) rainfall radar data that has been installed at the top of Merapi Mountain (Merapi Museum). It was confirmed that from June 2018 – June 2019, with 80.28 mm SWI, maximum values do not exceed the standard reference value of SWI (120 – 160 mm) set from JMA. It means that 80.28 mm of SWI value has not yet become the maximum limit of SWI value for lahar occurrence in the Boyong drainage area (BO-D5). The maximum limit of SWI value can be generated if sediment disaster occurrences are available.

Evaluation of Sediment Yield and Risk Management of Sediment Disaster With the Natural Resources Conservation Service-Curve Number Method

Subtropical areas are often struck by typhoons. The sediment disasters that accompany typhoons severely affect the environment. However, sediment yield (SY) data usually lack integrity. This study used long-term daily river discharge and SY data to establish a runoff–SY rating curve (Q–Qs rating curve) and used it to estimate the SY of typhoon events. In addition, based on the curve number, this study analyzed the relationship between the potential maximum retention (S) and SY; the results showed that different amounts of cumulative rainfall correspond to different S–SY functions; thus, the potential maximum erosion (A) of the catchment area could be estimated using this characteristic. For a sediment management strategy, this study took subdivisions as a unit and incorporated the potential maximum erosion (A) and slope to establish a map indicating the spatial distribution of sediment disaster risks. To determine the priority areas for management, the relationship between the cumulative number of subdivisions and landslide rate could be used to determine the areas with high potential, which can serve as a reference for related management research.