Environmental Engineering Reference
In-Depth Information
dimensionless parameters u
∗
/
v
and
w
s
/
u
∗
are given for any point of the
=
canal (
i
0, 1, 2 to
n
).
These
variables
are
determined
according
to
the
following
procedure:
- the
x
value is fixed according to the required degree of accuracy for the
numerical solutions and the need for representing the adaptation of the
actual non-equilibrium condition to the sediment transport capacity
(the equilibrium condition) of the canal. The
x
value should be much
smaller than the adaptation length (
L
A
) of the actual sediment transport
to the sediment transport capacity (equilibrium concentration);
- computation of the
L
A
-value. For the local flow conditions the value of
w
s
/
u
∗
,
u
∗
/
v
and the water depth are known in advance. The maximum
values of the parameter
w
s
/
u
∗
should satisfy the requirements for the
validity of the depth-integrated model (Ribberink, 1986);
- once the motion of sediment has been initiated, the values of the de
Chézy coefficient can be estimated depending on the type of roughness
along the wetted perimeter of the canal by:
18 log
12
R
k
s
C
=
for single roughness
(6.7)
18 log
12
R
k
se
C
e
=
for composite roughness
(6.8)
- the value of the depth-averaged equilibrium concentration
C
e
will be
determined by one of the sediment transport predictors, for example
Ackers-White, Brownlie or Engelund-Hansen. The predictors compute
the sediment transport per unit width (
q
s
), which is determined by the
local flow conditions and the sediment properties. The total sediment
transport across the whole canal section
Q
se
is calculated by:
Q
se
=
αBq
s
(6.9)
- next, the equilibrium concentration
c
e
is calculated by:
ρ
s
ρ
Q
s
Q
10
6
∗
c
e
=
(ppm)
(6.10)
- some internal conditions along the canal can be taken into account
for the computation of the sediment distribution either at boundaries
between canal reaches or at branches (bifurcations or confluences).
Application of the continuity for the water flow and for the sediment
transport is effective when changes either in bottom width or bottom
Search WWH ::
Custom Search