Geoscience Reference
In-Depth Information
Calculate overland-
flow hydraulics
Ye s
Re > 500 ?
Calculate raindrop
detachment
Detachment
No
Calculate raindrop
detachment
Add flow
detachment
Ye s
Ye s
flow depth
> 0 ?
u
*
> u
**
,
?
φ
Modify detachment
for flow depth
Transport
No
No
Transport sediment
by splash
Transport sediment
by unconcentrated flow
Transport sediment
by concentrated flow
Transport sediment
in suspension
Calculate deposition
by splash
Calculate deposition
along flowlines
Deposition
Sediment discharge
Calculate sediment
mass balance
Figure 11.11
Key thresholds in detachment and transport processes in overland flows (after Wainwright
et al.
, 2008).
11.5
Erosion processes on hillslopes
surface sealing are also dynamic over the duration of a
storm as small-scale roughness elements (Slattery and
Bryan, 1992). On noncultivated slopes, rills may form
a dynamic feedback between roughness and infiltration
characteristics, enhancing connectivity of the surface
(Muller, Wainwright and Parsons, 2008). This observation
emphasises the r ole of geomorphic feedbacks in control-
ling the functional connectivity of the system, requiring
a recognition of the discontinuity or continuity of the
various erosion processes along a slope. In many dry-
land systems, the interactions of continuity of water and
sediment movement, and consequently the distribution of
nutrients across the landscape, produce patterns of vege-
tation that further emphasise the connectivity of the land-
scape (Thornes, 1985, 1990; Wainwright, 2009a).
During a storm event, different processes of erosion will
be dominant at different points in time and at different
locations on the slope. To understand these patterns, it is
important to recognise the different processes of particle
detachment, entrainment, transport and deposition (Figure
11.11). Detachment refers to the loosening of materials at
the surface as a precursor to actual movement. It occurs
as the result of energy applied to a sediment particle by
raindrop impact or by flow, enhanced by the effects of
gravity on slopes. Entrainment is the initial movement of
the sediment at the surface and may under certain circum-
stances be continuous with the detachment process. It, too,
is controlled by the energy of raindrop impact and/or water
