Modeling of glacial lake outburst in the Shakhdara river basin using the complex of mathematical models

Abstract

<p>Climate change leads to the degradation of mountain glaciers in Central Asia and subsequent formation of glacial lakes [<em>Harrison et al., 2018</em>]. Due to the fact that glacial lakes are located, as a rule, in hard-to-reach areas, where there are no systematic observations, it is rather difficult to predict outbursts. One of the ways to assess the risks associated with glacial lakes outburst (GLOF) is mathematical modeling. We used a complex of three models to estimate possible hazard in the downstream valleys. A lake outburst hydrograph was obtained with a model developed by Yu.B. Vinogradov [<em>Vinodradov,1977</em>], based on the emergence and expansion of the intraglacial channel. For the debris flow source, we applied an upgraded transport-shift model, the equations were obtained using the data of the Chemolgan experiment [<em>Vinogradova, Vinogradov, 2017</em>].  A two-dimensional model called FLO-2D was used to investigate quantitative characteristics of the debris flow in the river valley [<em>O'Brien et al., 1993</em>]. The prerequisites and modeling of possible glacier lake outburst were considered for the Bodomdara River valley (Tajikistan) using detailed field data. According to the route survey results, it was established that Lake Bodomdara Upper is a glacial one, which, in turn, may lead to a cascade outburst flood. The bowl of Lake Bodomdara Lower is relatively stable, its outburst is possible without cascade flooding at anomalously high temperatures, snowmelt combined with extreme rainfall. Two probable scenarios were considered: I - the outburst of the Lake Bodomdara Lower (the volume was 328 thousand m<sup>3</sup> according to the bathymetric survey results) and II - the cascade outburst of the Lakes Bodomdara (with the volume of 700 thousand m<sup>3</sup>). A digital elevation model (DEM) ALOS PALSAR (12.5 m) was used as relief data, and for the Bodomdara river cone - DEM based on images from an unmanned aerial vehicle. The outburst flood hydrograph for the scenario I was obtained using the lake breakthrough model developed by Yu.B. Vinogradov, and for II - using an empirical formula. The material increment was estimated in the transport-shift model of debris flow formation. The resulting hydrograph was used for zoning the Bodomdara and Shahdara valleys with a total length of 75 km based on the FLO-2D model. According to the modelling results at the top of the estuary cone of the Bodomdara river discharge under scenario I, the maximum flow will be 111 m<sup>3</sup>/s, under scenario II - 525 m<sup>3</sup>/s.</p><p>1. Harrison S., Kargel J. S., Huggel C. et al. Climate change and the global pattern of moraine-dammed glacial lake outburst floods // The Cryosphere, 2018, vol. XII, 4, p. 1195–1209.</p><p>2. O'Brien J., Julien P., Fullerton W. Two-dimensional water flood, mudflow simulation // Journal of Hydraulic Engineering, ASCE, 1993, vol. CXIX, No 2, p. 244–259.</p><p>3. Vinogradova T.A., Vinogradov A.Yu. The experimental debris flows in the Chemolgan River basin // Natural Hazards, 2017, vol. LXXXVIII, 1, p. 189–198.</p><p>4. Vinogradov Yu.B. Glacial outburst floods and mudflows. Leningrad, Publishing House “Gidrometeoizdat”, 1977, 154 p.</p>