Badri Bhakta Shrestha

Driftwood deposition from debris flows at slit-check dams and fans

Experience shows that debris flows containing large woody debris (driftwood) can be more damaging than debris flows without driftwood. In this study, the deposition process of debris flows carrying driftwood was investigated using numerical simulations and flume experiments. Debris-flow trapping due to driftwood jamming in a slit-check dam was also investigated. A numerical model was developed with an interacting combination of Eulerian expression of the debris flow and Lagrangian expression of the driftwood, in which the fluctuating coordinates and rotation of the driftwood were treated stochastically. The calculated shapes and thicknesses of a debris-flow fan and the positions and orientations of the deposited driftwood on a debris-flow fan were consistent with experimental flume results. The jamming of driftwood in a slit-check dam was evaluated based on geometry and probability. The simulated results of outflow discharge and the proportion of driftwood passed through the slit-check dam also agreed with the experimental results.

Assessment of potential outburst floods from the Tsho Rolpa glacial lake in Nepal

Flood and sediment disasters caused by glacial lake outbursts have occurred frequently in recent years in the Himalayas of Nepal. Glacial lake outburst floods (GLOFs) can cause catastrophic flooding in downstream areas with serious damage to lives and property. It is thus important to investigate outburst floods from potentially dangerous glacial lakes. In this study, the characteristics of potential outburst floods from the Tsho Rolpa glacial lake due to two types of moraine dam failure caused by seepage flow or water overtopping were analyzed with various scenarios by using integrated modeling system of three numerical models: (1) the flow and bed-surface erosion model, (2) the seepage model and (3) the slope stability model. Flood inundation areas were also identified by using the numerical model of the flow and moraine dam failure and geographical information system tools. Possible threats and damages due to the potential GLOF events from the lake were also analyzed based on numerical results, flood inundation maps and field investigations.

Rapid Damage Assessment of Rice Crop After Large-Scale Flood in the Cambodian Floodplain Using Temporal Spatial Data

The objective of this study was to estimate rice crop damage over the entire Cambodia during a large flood event from July to November 2011. An integrated approach was applied to detect and monitor flood areas with flood depth and duration for near real-time rice crop damage estimation in 2011 by using MODIS time-series imagery. The combined data consists of developed MLSWI, EVI from MODIS, new FID from DEM, land use, and simplified empirical damage curves. These data are expected to play an important role in emergency response efforts and rapid risk assessment for high-risk flood areas in the Cambodian floodplain. A rice crop damage map will be generated, showing areas with different damage levels based on flood duration and floodwater depth, including 25% (8 days, below 1.5 m), 50% (8 days, over 1.5 m; 16 days, below 1.5 m), and 100% (16 days, over 1.5 m). The resulting map was validated and shows about 80% consistency with the government census based on field-scale investigation and survey.

Flood damage of the Pampanga River Basin by Typhoon Lando and Nona in 2015

2. 気象概要 フィリピン海を西進してきた台風 24 号は 10 月 18 日にル ソン島中部に上陸し、3~5 km/h で北西方向に移動して 19 日に南シナ海へと抜けた。10 月 17 日~19 日の降水量は、 パンパンガ川流域北東部の Gabaldon で 554 mm と観測地点 の中で最多を記録したが、下流域の Arayat では 172 mm、 Sulipan で 122 mm と東高西低の傾向が見られ、ほとんどの 地点で 18 日に多くの降水があった。一方、台風 27 号は 12 月 14 日にサマール島の北部を通過したあと、10~20 km/h でルソン島の南を西進し、16 日には南シナ海に抜けて北上 した。台風 24 号時に比べて降水量は多く、12 月 15 日~17 日の降水量は Gabaldon で 730 mm、Arayat で 154 mm を記録 し、Sulipan では 149 mm であった。