Roughness of a subglacial conduit under Hansbreen, Svalbard

Kenneth D. Mankoff, Jason D. Gulley, Slawek M. Tulaczyk, Matthew D. Covington, Xiaofeng Liu, Yunxiang Chen, Douglas I. Benn, Piotr S. GŁowacki

Research output: Contribution to journalArticlepeer-review

8 Scopus citations

Abstract

Hydraulic roughness exerts an important but poorly understood control on water pressure in subglacial conduits. Where relative roughness values are <5%, hydraulic roughness can be related to relative roughness using empirically-derived equations such as the Colebrook-White equation. General relationships between hydraulic roughness and relative roughness do not exist for relative roughness >5%. Here we report the first quantitative assessment of roughness heights and hydraulic diameters in a subglacial conduit. We measured roughness heights in a 125 m long section of a subglacial conduit using structure-from-motion to produce a digital surface model, and hand-measurements of the b-axis of rocks. We found roughness heights from 0.07 to 0.22 m and cross-sectional areas of 1-2 m2, resulting in relative roughness of 3-12% and >5% for most locations. A simple geometric model of varying conduit diameter shows that when the conduit is small relative roughness is >30% and has large variability. Our results suggest that parameterizations of conduit hydraulic roughness in subglacial hydrological models will remain challenging until hydraulic diameters exceed roughness heights by a factor of 20, or the conduit radius is >1 m for the roughness elements observed here.

Original languageEnglish (US)
Pages (from-to)423-435
Number of pages13
JournalJournal of Glaciology
Volume63
Issue number239
DOIs
StatePublished - Jun 1 2017

All Science Journal Classification (ASJC) codes

  • Earth-Surface Processes

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