Abstract
Understanding erosion and entrainment of material by debris flows is essential for predicting and modelling debris-flow volume growth and hazard potential. Recent advances in field, laboratory and modelling studies have distilled two driving forces behind debris-flow erosion: impact and shear forces. How erosion and these forces depend on debris-flow composition and interact remains unclear. Here, we experimentally investigate the effects of debris-flow composition and volume on erosion processes in a small-scale flume with a loosely packed bed. We quantify the effects of gravel, clay and solid fraction in the debris flow on bed erosion. Erosion increased linearly with gravel fraction and volume, and decreased with increasing solid fraction. Erosion was maximal around a volumetric clay fraction of 0.075 (fraction of the total solid volume). Under varying gravel fractions and flow volumes erosion was positively related to both impact and shear forces, while these forces themselves are also correlated. Results further show that internal dynamics driving the debris flows, quantified by Bagnold and Savage numbers, correlate with erosional processes and quantity. Impact forces became increasingly important for bed erosion with increasing grain size. The experiments with varying clay and solid fractions showed that the abundance and viscosity of the interstitial fluid affect debris-flow dynamics, erosional mechanisms and erosion magnitude. High viscosity of the interstitial fluid inhibits the mobility of the debris flow, the movement of the individual grains and the transfer of momentum to the bed by impacts, and therefore inhibits erosion. High solid content possibly decreases the pore pressures in the debris flow and the transport capacity, inhibiting erosion, despite high shear stresses and impact forces. Our results show that bed erosion quantities and mechanisms may vary between debris flows with contrasting composition, and stress that entrainment models and volume-growth predictions may be substantially improved by including compositional effects.
| Original language | English |
|---|---|
| Pages (from-to) | 2151-2169 |
| Number of pages | 19 |
| Journal | Earth Surface Processes and Landforms |
| Volume | 47 |
| Issue number | 8 |
| Early online date | 5 Apr 2022 |
| DOIs | |
| Publication status | Published - 30 Jun 2022 |
Bibliographical note
Funding Information:This work was supported by the Netherlands Organisation for Scientific Research (NWO) (grants 0.16.Veni.192.001 and OCENW.KLEIN.495 to TdH). The authors gratefully acknowledge Arjan van Eijk, Bas van Dam, Marcel van Maarseveen, Henk Markies and Mark Eijkelboom for their help with the design and construction of the flume and measurement set-up, as well as their assistance during the experiments. The authors would also like to gratefully acknowledge the assistance of Kees van Welsum in conducting the experiments and Maarten Kleinhans in providing us with a first internal review. We would also like to thank two anonymous reviewers. Their constructive feedback greatly improved this manuscript.
Funding Information:
This work was supported by the Netherlands Organisation for Scientific Research (NWO) (grants 0.16.Veni.192.001 and OCENW.KLEIN.495 to TdH). The authors gratefully acknowledge Arjan van Eijk, Bas van Dam, Marcel van Maarseveen, Henk Markies and Mark Eijkelboom for their help with the design and construction of the flume and measurement set‐up, as well as their assistance during the experiments. The authors would also like to gratefully acknowledge the assistance of Kees van Welsum in conducting the experiments and Maarten Kleinhans in providing us with a first internal review. We would also like to thank two anonymous reviewers. Their constructive feedback greatly improved this manuscript.
Publisher Copyright:
© 2022 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.
Keywords
- basal-shear force
- debris flow
- entrainment
- erosion
- experiments
- impact force