Stability of boulders on cobble streambeds

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 exper...

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Bibliographic Details
Published in:Water S. A. 2024-04, Vol.50 (2), p.201-210
Main Authors: Stols, K, James, C.S
Format: Article
Language:English
Subjects:
Acceleration
Analysis
Aquatic habitats
Boulders
Critical velocity
Density
Flow velocity
Gravity
Habitats
Heterogeneity
Incipient motion
Motion stability
Rehabilitation
Shear stress
Streambeds
Water density
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Summary: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. KEYWORDS boulders stability incipient motion critical velocity aquatic habitat
ISSN:0378-4738
DOI:10.17159/wsa/2024.v50.i2.4077