Geology Reference
In-Depth Information
Table 14.1
Hydrological, erosion and sediment transport processes modelled by SHETRAN Version 4.
(1)
Interception of rainfall on vegetation canopy (Rutter storage model)
(2)
Evaporation of intercepted rainfall, ground surface water and channel water; transpiration of water drawn from the root zone
(Penman-Monteith equation, or the ratio of actual to potential evapotranspiration as a function of soil moisture tension)
(3)
Snowpack development and snowmelt (temperature-based or energy budget methods)
(4)
Three-dimensional variably saturated subsurface flow (Darcy-Buckingham approach)
(5)
Two-dimensional overland flow; one-dimensional channel flow (Saint Venant equations)
(6)
Subsurface zone/surface water interaction and subsurface zone/channel interaction
(7)
Soil erosion by raindrop impact, leaf drip impact, overland flow and bank erosion (see text for equations)
(8)
Soil erosion by shallow landslide erosion (see text for equations)
(9)
Two-dimensional total load convection in overland flow by size fraction, including input to the channels; deposition and
resuspension of sediments in overland flow (mass conservation equation incorporating Engelund-Hansen total load and Yalin
bedload transport capacity equations)
(10)
One-dimensional convection of cohesive and non-cohesive sediments in channel flow by size fraction; deposition and resuspension
of non-cohesive sediments in channel flow; channel bed erosion by channel flow (mass conservation equation incorporating
Ackers-White and Engelund-Hansen transport capacity equations)
(11)
Transport of contaminants adsorbed to sediment particles (convection-dispersion equation with partition distribution coefficient)
processes, such as landslide erosion, available in
Version 4. The chief distinguishing feature of this
version, in terms of physical processes, is the rep-
resentation of the subsurface by a fully three-
dimensional variably saturated subsurface scheme
which enables such features as perched water
tables and hypodermic flow (i.e. just below the
ground surface) to be modelled. Importantly
for erosion modelling, SHETRAN generates over-
land flow both by an excess of rainfall over infil-
tration, and by upward saturation of the soil
column.
and Bathurst (1996). However, it will be helpful
to know that the equations for determining soil
erosion are:
for raindrop and leaf drip impact:
D
r
=
k
r
F
w
(1
−
C
g
−
C
r
)(
M
r
+
M
d
)
(14.1)
and for overland flow:
æ
ö
C
t
(
)
Dk
=
1
-
-
1
for
tt
>
(14.2a)
ç
÷
f
f
r
c
t
è
ø
c
D
f
=
0 for
t
≤
t
c
(14.2b)
14.3.2
SHETRAN erosion and sediment
yield component
where
D
r
and
D
f
are the respective rates of detach-
ment of material per unit area (kg m
−2
s
−1
);
k
r
is
the raindrop impact soil erodibility coefficient
(J
−1
);
k
f
is the overland flow soil erodibility coeffi-
cient (kg m
−2
s
−1
);
C
g
is the proportion of ground
protected from drop/drip erosion by near-ground
cover such as low vegetation (range 0-1);
C
r
is the
proportion of ground protected against drop/drip
erosion and overland flow erosion by, for exam-
ple, a cover of loose rocks (range 0-1);
M
r
is the
momentum squared for raindrops falling directly
on the ground ((kg m s
−1
) m
−2
s
−1
);
M
d
is the momen-
tum squared for leaf drip ((kg m s
−1
) m
−2
s
−1
);
Subcomponents account for soil erosion by rain-
drop impact, leaf drip impact and overland flow,
channel bed and bank erosion by channel flow,
and sediment transport by overland and channel
flow (Table 14.1). The component is driven by
inputs from the hydrological (water flow) simula-
tions, but feedback to the flow simulations is not
modelled as the effects are unlikely to be signifi-
cant at the sediment concentrations and relative
scales of erosion and deposition typically consid-
ered. Detailed descriptions of the subcomponents
are provided in the above references and Wicks
