Stability of boulders on cobble streambeds

Authors

  • K Stols School of Civil & Environmental Engineering, University of the Witwatersrand, Private Bag 3, Wits 2050, Johannesburg, South Africa
  • CS James School of Civil & Environmental Engineering, University of the Witwatersrand, Private Bag 3, Wits 2050, Johannesburg, South Africa

DOI:

https://doi.org/10.17159/wsa/2024.v50.i2.4077

Keywords:

boulders, stability, incipient motion, critical velocity, aquatic habitat

Abstract

The placement of boulders in streams enhances aquatic habitat by increasing the heterogeneity of flow conditions.  Practical design must ensure the stability of individual boulders, requiring calculation of their incipient movement conditions.  The stability of a boulder on a cobble bed is shown experimentally to depend on its size, the bed material size, the degree of embedment of the boulder, the slope of the bed and the flow velocity and depth.  An equation is derived through a pivoting analysis for predicting the relationship between the critical ambient depth-averaged velocity and the critical flow depth; this, together with a resistance equation, can be used to predict the flow conditions for boulder stability.  The equation is used to develop a simpler form for unsubmerged spherical boulders and cobbles.  The stability equation is tested against the experimental data, using an experimentally determined drag coefficient relationship.

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Published

2024-04-30

How to Cite

K Stols, & CS James. (2024). Stability of boulders on cobble streambeds. Water SA, 50(2 April). https://doi.org/10.17159/wsa/2024.v50.i2.4077

Issue

Vol. 50 No. 2 April (2024): Water SA

Section

Research paper

License

Copyright (c) 2024 K Stols, CS James

Creative Commons License

This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License.

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