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Coastal Engineering: Theory and Practice
that in the absence of friction.
R
Hi
.
7T
7T
for — < a < —
4
2
(6-5)
Table 6.1. Roughness coefficients for different surface textures (various sources)
as reported by Reeve et al. [2012].
Type of slope protection
Roughness
coefficient, r
Roughness factor from
EurOtop,
Smooth concrète or asphalt
1.0
1.0
Smooth concrète blocks with little or
no drainage
1.0
1.0
Stone blocks pitched or mortared
0.95
1 /4 stone set 10 cm higher
0.9
Stepped
0.9
Turf
0.85-0.9
1.0
Basait
0.9
Rough concrète
0.85
Small blocks over 1/25 surface
0.85
Small blocks over 1/9 surface
0.8
One layer of rock armour or an
imperméable base
0.8
0.60
Open stone asphalt
0.8
Stones set in cernent, rag stone etc.
0.75-0.8
Ribs (spacing /width = 7,
height/width = 5-8)
0.75
Fully grouted stone
0.6-0.8
Partially grouted stone
0.6-0.7
Rounded stones
0.6-0.7
One layer of rock armour on a
permeable base
0.55-0.60
0.45
Two layers of rock armour
0.5-0.6
0.55 (imperméable cote)
0.40 (permeable core)
Hollow cube armour units, one layer
0.5
Antifiers
0.47
Dolos and Accropode™ armour units
0.4
0.46
XblocR
0.45
CORE-LOCr
0.44
Stabit armour units
0.35-0.4
Tetrapods, two layers
0.3
0.38