Linking debris-flow hazard assessments with geomorphology

Author(s)

Thomas Glade

Abstract

Debris-flow hazard assessment schemes are commonly based on empirical, physical, or numerical methods and techniques.

Inherent in all methods is generally the assumption of unlimited sediment supply. This study compares model inputs of

sediment requirements for debris flows with estimated sediment reproduction from both solifluction and rockwall retreat. The

analysis is carried out in Bı¿ldudalur, a community in the Westfjords of Iceland. Geomorphic techniques are applied to determine

the set of natural processes acting in this landscape to estimate spatial distribution of relevant processes, to approximate level of

processes activity, and to provide information for scenario modeling. Debris-flow volumes are determined by coupling rainfall

magnitudes and catchment sizes with average sediment contents. Rockwall retreat and solifluction rates are based on literature

reviews.

For a rainstorm with a 10-year return period, debris-flow volumes are calculated for 12 different creeks. Rates are assumed

for solifluction with a velocity of 0.25 m/yr at an average depth of 0.5 m and for rockwall retreat with 2 mm/yr. Comparing

sediment requirements with estimated sediment reproduction leads to a factor of deficit ranging between 6.2 and 8.5. Thus, the

sediment storage is not refilled as fast as the next potential triggering rainfall occurs. Consequently, if a debris flow has occurred

in the past, all sediment is removed, and the following rainstorm event is djustT causing a flood, which is by far less destructive

than a debris-flow event. The challenge of future debris-flow hazard-assessment schemes is to include geomorphic analysis to

be able to obtain more sustainable results.

Organisation(s)

Department of Geography and Regional Research

Journal

Geomorphology

Volume

66

Pages

189-213

No. of pages

25

ISSN

0169-555X

Publication date

2006

Peer reviewed

Yes

Austrian Fields of Science 2012

105404 Geomorphology

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