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Effect of sill spacing and sediment size grading on scouring at grade‐control structures
Author(s) -
Marion Andrea,
Lenzi Mario A.,
Comiti Francesco
Publication year - 2004
Publication title -
earth surface processes and landforms
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.294
H-Index - 127
eISSN - 1096-9837
pISSN - 0197-9337
DOI - 10.1002/esp.1081
Subject(s) - sill , sediment , geology , erosion , gradation , streams , hydrology (agriculture) , geometry , geotechnical engineering , soil science , geomorphology , mathematics , petrology , computer science , computer network , computer vision
Sequences of articial steps are sometimes used to reproduce the natural step–pool morphology of high‐gradient streams. The depth, length and shape of the scour holes in gravel‐bed rivers can be predicted reasonably using recently developed formulae. However, the properties of the scour holes can sometimes be affected by the distance between structures. This effect is called ‘geometrical interference’ and leads to a reduction of the scour hole compared to its potential size. Geometrical interference may occur in sequences of articial steps in high‐gradient torrents, where structures are sometimes built at distances of a few tens of metres apart, but may also apply to natural step–pool systems. In this paper, a series of tests have been conducted to determine the effect of bed sill spacing and sediment grading on the potential erosion by jets forming over the sills. A new formula is derived, applicable to high‐gradient streams (slope > 0·04), which can be applied to the special case of scour holes developed by interfering sills. Sediment size gradation, not accounted for in previous formulae, is found to have a signicant effect on the scour dimensions and is included in the new predictive formula. Copyright © 2004 John Wiley & Sons, Ltd.