Item: THE DESIGN AND CONSTRUCTION OF SLUSH-FLOW NETS IN VANNLEDNINGSDALEN LONGYEARBYEN SVALBARD
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Title: THE DESIGN AND CONSTRUCTION OF SLUSH-FLOW NETS IN VANNLEDNINGSDALEN LONGYEARBYEN SVALBARD
Proceedings: International Snow Science Workshop 2024, Tromsø, Norway
Authors:
- Arni Jonsson [ The Norwegian Water Resources and Energy Directorate (NVE) ]
- Nadine Feiger [ Geobrugg AG ]
- Inger Lise Solli [ Rambøll Norge AS ]
- Marit Bratland Pedersen [ Rambøll Norge AS ]
- Mathias Klotz [ DS Entreprenør AS ]
- Anders Ringheim [ SNSK Longyearbyen ]
- Stian Bue Kanstad [ The Norwegian Water Resources and Energy Directorate (NVE) ]
- Jan-André Jansen [ The Norwegian Water Resources and Energy Directorate (NVE) ]
- Oddmund Sletten [ DS Entreprenør AS ]
Date: 2024-09-23
Abstract: Slush-flows from Vannledningsdalen valley in Longyearbyen Svalbard have posed a threat to the residential area on Haugen and below Sukkertoppen mountain in springtime. For decades, the municipality has been trenching the snowpack in Vannledningsdalen in late May to drain the snow-pack and reduce slush-flow risk. To reduce the threat from slush-flows, various mitigation measures were considered, including the use of deflecting dams and modified debris-flow nets. The municipality decided to implement the net solution. The height of the construction ranges from 4 m to 8 m and includes fourteen nets strategically placed along roughly 1200 m of the valley floor. Debris-flow nets have not been previously used on such a large scale for the purpose of mitigating slush-flows. The criterion for their dimensions is not firmly established but it is believed that the rheology and dynamics of slush-flows are akin to those of debris-flows. As a result, the load assessment for the planned nets relies on the understanding and techniques used for debris-flows nets. One of the issues was to define the size of the slush-flow release between the nets and how the slush-flow would react to the nets. RAMMS::DEBRIS FLOW was used to estimate the loading. Based on the defined loads, static and dynamic verifications for the load-bearing capacity of the different slush flow barriers were carried out, leading to the final design of each net and barrier components. The thickness of the active layer is estimated to be between 1.0 and 1.5 m in the valley, based on thermistor measurements. Due to predicted climate changes, a vertical thickness of the active layer of 2.0 m and 2.5 m is used as a project basis. The rockmass in Vannledningsdalen is mainly a layered sandstone/siltstone/shale/slate of various competence and with layers of coal in some locations. The anchors of the nets are designed to withstand creeping forces, frost heave induced forces, increased active layer thickness and increased weathering of rock mass during the lifetime of the nets. Construction work began in 2023 with foundations and side anchors and the work will be finalized later in 2024. Three barriers are already installed.
Object ID: ISSW2024_P7.13.pdf
Language of Article: English
Presenter(s): Arni Jonsson
Keywords: Mitigation measures, slush-flow, debris-flow nets, Vannledningsdalen, Svalbard
Page Number(s): 954 - 961
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