TY  - JOUR
A1  - Bricker, Jeremy D.
A1  - Schwanghart, Wolfgang
A1  - Adhikari, Basanta Raj
A1  - Moriguchi, Shuji
A1  - Roeber, Volker
A1  - Giri, Sanjay
T1  - Performance of Models for Flash Flood Warning and Hazard Assessment
BT  - the 2015 Kali Gandaki Landslide Dam Breach in Nepal
JF  - Mountain research and development
N2  - The 2015 magnitude 7.8 Gorkha earthquake and its aftershocks weakened mountain slopes in Nepal. Co- and postseismic landsliding and the formation of landslide-dammed lakes along steeply dissected valleys were widespread, among them a landslide that dammed the Kali Gandaki River. Overtopping of the landslide dam resulted in a flash flood downstream, though casualties were prevented because of timely evacuation of low-lying areas. We hindcast the flood using the BREACH physically based dam-break model for upstream hydrograph generation, and compared the resulting maximum flow rate with those resulting from various empirical formulas and a simplified hydrograph based on published observations. Subsequent modeling of downstream flood propagation was compromised by a coarse-resolution digital elevation model with several artifacts. Thus, we used a digital-elevation-model preprocessing technique that combined carving and smoothing to derive topographic data. We then applied the 1-dimensional HEC-RAS model for downstream flood routing, and compared it to the 2-dimensional Delft-FLOW model. Simulations were validated using rectified frames of a video recorded by a resident during the flood in the village of Beni, allowing estimation of maximum flow depth and speed. Results show that hydrological smoothing is necessary when using coarse topographic data (such as SRTM or ASTER), as using raw topography underestimates flow depth and speed and overestimates flood wave arrival lag time. Results also show that the 2-dimensional model produces more accurate results than the 1-dimensional model but the 1-dimensional model generates a more conservative result and can be run in a much shorter time. Therefore, a 2-dimensional model is recommended for hazard assessment and planning, whereas a 1-dimensional model would facilitate real-time warning declaration.
KW  - Nepal
KW  - earthquake
KW  - landslide dam breach
KW  - flood
KW  - HEC-RAS
KW  - Delft-FLOW
KW  - steep mountain stream
Y1  - 2017
U6  - https://doi.org/10.1659/MRD-JOURNAL-D-16-00043.1
SN  - 0276-4741
SN  - 1994-7151
VL  - 37
IS  - 1
SP  - 5
EP  - 15
PB  - International Mountain Society
CY  - Lawrence
ER  -