SCENARIO-BASED MODELLING OF GLACIAL LAKE OUTBURST FLOOD AND ASSESSMENT OF ITS IMPACT IN DOWNSTREAM AREA: A Case Study of a glacial lake in Jostedalsbreen Ice Cap, Norway

Abstract

With the increased melting and retreat of glaciers as an effect of climate change, the number and size of glacial lakes are increasing, putting the downstream communities in the Arctic region at risk. Jostedalsbreen Ice Cap in Western Norway is facing a similar problem where new lakes are formed, and existing lakes have been found expanded in recent years. In recent decades, the number of Glacial Lakes Outburst Flood (GLOF) events have also been recorded to increase in number and some lakes are expected to be potentially dangerous. That is why it is important to assess the impact of potential GLOFs in such areas so that the planners and local authorities can make plans accordingly and prepare the downstream communities to avoid or reduce potential disasters.

In this context, this study utilizes the 2-dimensional Hydrodynamic modelling tool, HEC RAS to model the dam breach and inundation flood generated due to GLOF in a potentially dangerous moraine dammed lake in Jostedalsbreen region. The study also utilizes the empirical formula to derive mean depth, total volume, drainage volume, and peak discharge of lake water from the lake surface area. The outburst duration, peak discharge and manning’s roughness coefficient are varied in a way to assume three different scenarios (Optimistic, Intermediate and Pessimistic) to assess the impact of flood (2-meter water depth) in downstream area.

The result of the study showed least impact in Optimistic scenario with 23 buildings, 4.80 km of river section and 2.64 km2 of land surface area affected under flood. However, the highest impact was observed in the Intermediate scenario where 35 buildings, 6.47 km of river sections and 3.68 km2 of land surface area were affected by the flood rather than in Pessimistic scenario. This could be because of the change in water course due to terrain feature, roughness coefficient, and difference in the velocity of flow which avoided some buildings, river sections and land surface area in Pessimistic scenarios. This method is very economical because of the use of open-source software like HEC RAS, QGIS, and empirical formula and it at least helps the planners and local authorities to anticipate the range of impact different scenarios could create in downstream areas. Nevertheless, it is crucial to study the geomorphology of glacial lakes, moraine dam and potential flow path to model the impact with higher precision.