Modelling Glacial Lake Outburst Flood Discharge in the Rio Huemules, Northern Patagonian Icefield

The Northern Patagonian Icefield is one of the most rapidly changing ice masses on Earth and drains cold sediment laden fresh water into the critical aquatic zone of the Patagonian fjords. Glacial retreat and the growth of glacial lakes has caused repeated glacial lake outburst floods (GLOFs) in several rivers draining the icefield, but to date few studies have detailed flood hydrographs. This thesis presents a high resolution, multi-year discharge record for the Rio Huemules, a major river draining Steffen Glacier, third-largest glacier of the Northern Patagonian Icefield. To construct the discharge record, a rating was developed which combines fluorometric discharge gaugings at low stage and hydraulic modelling to estimate the stage—discharge relationship at peak flows. The rating was corroborated by comparison with discharge estimated using source lake volume and the Clague—Matthews relationship for subglacial pipe flow. Four GLOFs are documented, each with discharges exceeding 1000 m3/s. The largest event occurred in December 2016, reaching a peak discharge of 3432 m3/s ± 25% after an outburst flood from the Laguna de los Tempanos. As Steffen Glacier undergoes accelerating retreat, the water storage capacity of the Laguna de los Tempanos is diminishing, resulting in a decline in GLOF magnitude in the Rio Huemules. However, as retreat of the main glacier trunk progresses up valley, a roughly 0.2 km3 lake to the north of Laguna de los Tempanos may enter a GLOF phase in the near future, potentially leading to flood discharges exceeding 3000 m3/s. This rating contributes to risk management for families in the Lower Huemules valley and adds to studies on the catchment water balance for the Steffen Glacier system and regional biogeochemical cycles.