Results - Response of Flood Events to Land Use and Climate Change - page 144

Table 6.8 The detailed information about selected cross sections and their locations (unit: m)
ID Shape length Station Left bank Right bank L-length C-length R-length
a 30.331 8967.123 0.075 0.835 499.36 498.80 499.96
b 20.801 8469.964 0.111 0.803 505.91 502.32 495.81
c 25.206 8216.966 0.184 0.876 248.37 246.56 244.49
d 84.362 4469.889 0.072 0.886 4224.3 3754.5 3866.2
e 78.260 3716.019 0.029 0.985 794.70 751.73 788.14
f 37.197 1716.146 0.022 0.916 2056.4 2001.6 2057.2
g 25.528 1462.520 0.063 0.872 232.54 241.46 247.31
h 27.313 1221.056 0.004 0.870 249.64 247.15 246.96
i 28.784 1.52419 0.024 0.960 969.17 973.90 980.11
Shape length represents the length of each cross section; Station represents the distance of each
cross section from the upstream; Left bank and Right bank represent the length of cross sections
between both left and right sides; L-length represents the distance between two cross sections at
the left points; C-length represents the distance between two cross sections at the center points;
R-length represents the distance between two cross sections at the right points
defined for each cross section. In HEC-RAS, it was needed to play with the height
of the dykes-the left and right bank of cross sections calibrated the model based on
the observed data. Table 6.8 represents some necessary information related to each
cross section. For example, Object ID (2) represents the second cross section
which is located upstream at station 8469.9648. The L-length shows the distance
between the second cross section and the previous one on the left side. C-length
shows the distance between the second cross section and the previous one in the
channel, and R-length shows the distance between the second cross section and the
previous one on the right side, and so on.
Ubaye River is divided into three parts: (1) Upstream or channelized part of the
river in city area; (2) Middle part of the river in natural environment when the river
starts to get wider; (3) Downstream part of the river in natural environment when
the river starts to get narrow again. Cross sections should be added at locations
where changes occur in slope, width, and roughness. Therefore, to select the cross
section's location with respect to all mentioned parameters, 10 cross sections were
applied along the river and the data were manually imported to SOBEK model.
Applying more than 10 cross sections in SOBEK made the modeling simulation
unstable. The interval between cross sections was selected 150 m, with a total river
section of 10 km in length. The cross sections which were created in HEC-Geo-
RAS were directly imported to HEC-RAS. In HEC-RAS, there was the possibility
to interpolate the cross sections every 20 m. In order to create a more reliable flood
modeling result (2D) in HEC-RAS, the extension of the cross sections in the
floodplain area was considered mandatory.
As shown in Fig. 6.15 , extension of cross section in the floodplain made the
model unstable. To prevent such as this kind of error it was needed to modified
dykes and roughness values for each cross section manually.