Geomorphic Change Caused by Flood at Scott River Alluvial Fan

Abstract

<p>A four-day glacier-melt flood (13-16 August, 2013) caused an abrupt geomorphic change in the proglacial gravel-bed Scott River, that drains the small (10 km2) Scott Glacier catchment (SE Svalbard). This type of floods occur on Svalbard increasingly during periods of abnormally warm or rainy weather in summer or early autumn, and the probability of occurrence grows in direct proportion to the increase in temperature and/or precipitation intensity. In the summer 2013 measurement season, the highest daily precipitation (17 mm) occurred on August 13. During the following four days, it constituted in total 47mm i.e. 50% of the precipitation total for the measurement period of 2013. The largest flood in 20 years, was caused by high precipitation with a synchronous rise in temperature from about 1.0 to 8.6 °C. These values exceeded multi-year averages (32 mm and 5.0 °C, respectively), at average discharge 0.9 m3·s–1 (melt season mean 1986–2011). These conditions caused a rapid and abrupt response of the river with dominant (90%) glacier-fed. The increase of discharge to 4.6 m3·s–1, initiated by the glacial flood, mobilized significant amounts of sediment in the river bed and channel. Geomorphic changes within the alluvial fan as area of 58,820 m2, located at the mouth of the Scott River, were recorded by multi-sites terrestrial laser scanning using a Leica Scan Station C10, and then estimated using Geomorphic Change Detection (GCD) Software. Flood-induced total area of lowering (erosion) covered 38% of the alluvial fan (6,030 m2), resulting in the removal of 1,182 ± 121 m3 of sediment volume. During the final phase of the flood, two times more sediments (1,919 ± 344 m3) was re-deposited within the alluvial fan surface, causing significant aggradation on 62% of its area (17,190m2). These geomorphic changes resulted in an average lowering (erosion) of the alluvial fan surface of 0.2 m and an average rising (deposition) of 0.1 m.</p>