Geoscience Reference
In-Depth Information
(a)
3
3
3
3
2
22
2
111
1
11
111111
1
111
2
3
1
Re
(b)
4
C1 (plot 3)
C2 (plot 3)
C1 (plot 6)
3
2
1
0.9
0.8
0.7
0.6
1000
2000
5000
Re
Figure 11.9
Hypothetical relationships between the Darcy-Weisbach friction factor and flow Reynolds number and measured
relationships on surfaces from Walnut Gulch, Arizona (Abrahams, Parsons and Luk, 1990).
varies with soil characteristics (Bryan, 2000). It is thus
necessary to relate current flow conditions to the observed
roughness, with important feedbacks in the dynamics of
runoff and erosion processes (Figure 11.9).
This apparent complexity raises a wider conceptual
issue of what surface roughness actually
is
and, conse-
and Wainwright (1994) demonstrated that different tech-
niques of measurement are underpinned by different as-
sumptions about flow roughness, and can produce very
different estimates of roughness for the same surfaces.
Lane (2005) defines roughness as that component of to-
pography that must be dealt with implicitly at the scale
