Methodology - Response of Flood Events to Land Use and Climate Change - page 74

Chezy coefficient C may be determined in a number of ways, referring to various
formulations, e.g., Chezy, manning. In particular, if a Manning value is provided,
the Chezy coefficient is calculated as:

C ¼ R 0 : 125
n

ð 3 : 27 Þ

SOBEK overland flow consists of a 2D modeling system based on a subset of the
shallow water equations as follows:

o h

ot þ o ð uh Þ

þ o ð vh Þ
oy

¼ 0 ð 3 : 28 Þ

ox

u

p

o u

ot þ u o u ox þ v o u oy þ g o ð h þ z b Þ

u 2 þ v 2

þ C f ¼ 0 ð 3 : 29 Þ

ox h

u

p

ov

ot þ u o v ox þ v o v oy þ g o ð h þ z b Þ

u 2 þ v 2

þ C f ¼ 0 ð 3 : 30 Þ

oy h

1 = 2

V ¼ u 2 þ v 2 ð 3 : 31 Þ

where, x and y represent the orthogonal axis; u and v the velocity vectors along
these axis, respectively. The staggered grid shown in Fig. 3.10 shows that water
level (h) and flow velocity vectors (u and v) are computed at alternating grid
points. The flow velocity (v) can be computed as the vector sum of the vector
velocities u and v.
The SOBEK software package integrates a 1D modeling package with a 2D
hydrodynamic prediction package. Thus, it has the functionality of including the
one-dimensional river/channel flow and two-dimensional overland flow, which is
called ''SOBEK 1D-2D'' ([ 66 ]; SOBEK User's Manual [ 67 ], www.sobek.nl ) .
Figure 3.11 represents the modeling process in SOBEK.
The SOBEK software package integrates a 1D modeling package with a 2D
hydrodynamic prediction package. Thus, it has the functionality of including the
1D river/channel flow and 2D overland flow, which is called ''SOBEK 1D-2D''
([ 66 ]; SOBEK User's Manual [ 67 ], www.sobek.nl ). Figure 3.6 represents the
modeling process in SOBEK.
The data input and editing interface in SOBEK is called NETTER. NETTER
offers the possibility to set up the schematization and also offers advanced analysis
tools to show model results. NETTER has two editing models: (a) for setting up
the schematization (e.g., by editing new nodes); and (b) for editing the attribute
data. NETTER also provides two separate menu bars to input and edit 1D feature
(drainage channel) and 2D grid layers representing floodplains ([ 66 ]; SOBEK
User's Manual [ 67 ]).
Before starting schematization it is important to have DEM imported to the
NETTER, which was developed in ArcGIS, and imported directly to the sche-
matization environment as an Ascii format using ''2D grid'' tools. Then, the flow