RESEARCH ARTICLE Hydraulic Reconstruction of the 1818 Giétro Glacial Lake 10.1029/2019WR025274 Outburst Flood Key Points: 1 2 3 3 3 1 • The 1818 Giétro flood was one of the C. Ancey , E. Bardou , M. Funk , M. Huss ,M.A.Werder , and T. Trewhela world's major glacial lake outburst 1 2 floods in historical times Hydraulics Laboratory, École Polytechnique Fédérale de Lausanne, Lausanne, Switzerland, DSM Consulting, Nax, • We apply a simple computational Switzerland, 3Laboratory of Hydraulics, Hydrology and Glaciology (VAW), ETH Zurich, Zurich, Switzerland framework to reconstruct the initial hydrograph and flood motion • Flow resistance was significant, Abstract In the spring of 1818, ice avalanches from the Giétro Glacier created an ice dam, which in presumably because of intense sediment and debris transport turn formed a glacial lake in the Drance Valley (Canton of Valais, Switzerland). Today, its maximum volume is estimated to have been 25 × 106 m3. Cantonal authorities commissioned an engineer named Ignaz Venetz to mitigate the risk of the ice dam's failure. He supervised the construction of a tunnel Supporting Information: 6 3 • Supporting Information S1 through which a large volume of water was drained as the lake rose (9 × 10 m according to his estimates and 11 × 106 m3 according to our model). After 2.5 days of slow drainage, the ice dam failed on 16 June 1818 and caused major flooding in the Drance Valley up to 40 km downstream, resulting in about 40 Correspondence to: C. Ancey, deaths. Venetz's lake monitoring notes, numerous testimonies gathered in the disaster's aftermath, and our
[email protected] field survey have made it possible to collect a wealth of information on this event, which is one of the world's major documented glacial lake outburst floods.