Environmental Engineering Reference
In-Depth Information
where extreme refinement is required to correctly
represent the river channel geometry.
Several numerical techniques exist to date to
link 1D and 2D models. The most widely used
technique for 1D river and 2Dfloodplain linking is
the lateral link (Fig. 12.6), where the exchange
flows are based on water level differences and
typically modelled using broad-crested weir equa-
tions or depth-discharge curves (Lin et al. 2006;
Danish Hydraulic Institute 2007a; Evans et al.
2007; Liang et al. 2007b; BMT-WBM 2008). A
limitation of the approach is that the complicated
momentum exchange processes that characterize
the river-floodplain boundary are not modelled.
These processes intimately depend on complex
3D flow patterns occurring in the river (Morvan
et al. 2002), which by definition are not resolved
in a 1D river model. Progress towards improved
model
to be used in association with DEM grids in com-
puter models (Romano 2004; Brzank et al. 2005;
Liu 2008).
Recent, Ongoing and Future Research
Challenges
Hybrid 1D/2D methods
Although the ability to link 1D and 2Dmodels has
existed in theory for several decades, is has only
recently been implemented in commercial soft-
ware packages (Syme 1991; Evans et al., 2007). It is
now becoming increasingly popular because it
allows modellers to exploit the respective advan-
tages offered by 1D and 2D models (see above).
Possible applications of 1D/2D linking are:
.
within a channel that onewishes tomodel partly
in 1D and partly in 2D;
.
between a 1D drainage network model and a 2D
surface flood model;
.
between a 1D river model and a 2D floodplain
model;
.
within a mainly 2D model where, for example,
culverts are modelled in 1D, linking 2D cells to
each other.
For example modellers can take advantage of
the established tradition of 1D river modelling
while at the same time modelling floodplains in
two dimensions. It also results in significant
computational savings over fully 2D approaches
representation is
reported in Liang
et al. (2007b).
One may also use a longitudinal link (Fig. 12.6)
to model a watercourse partly in 1D (upstream)
and partly in 2D (downstream), or to connect
the downstream extremity of a 1D model to a
2D grid (Danish Hydraulic Institute 2007a; Evans
et al. 2007; Liang et al. 2007b). In this approach the
flow from the 1D model enters the 2D model as
a 'source', and the water level in the 2D model at
the junction is used as a downstream boundary
condition in the 1D model. Some combined
1D/2D models also offer the possibility to use
1D components to represent pipes or culverts
Fig. 12.6
Schematic illustration of the lateral (“Connection 1”) and longitudinal (“Connection 2”) connectionmodes.
In a lateral link the discharge Q
L
is calculated usually as a function of the upstream and downstreamwater elevations
and crest elevation (respectively Z
S1
,Z
S1
and Z
W
). From Liang et al. (2007b).
