Results - Response of Flood Events to Land Use and Climate Change - page 156

(a) (a)

(b) (b)

Fig. 6.24 Comparison of river cross sections at two different points. a DEM with 10 m
resolution; b DEM with 5 m resolution

resolution. This may be due to the fact that a 10 m resolution DEM ignores and
generalizes surface features which affect the water flow. Therefore, the preferential
water paths are not well defined. The results of the 10 m DEM simulation show
that the flow distribution shifted from the actual flow paths in locations of the
generated river network. It was obvious that the flood mainly occurred due to
overflow in the rivers, which was perhaps due to the negligence of the locally
elevated lands such as dykes and roads in the model. In the real situation, these
elevated lands blocked the movement of flooding from the riverside to other side.
However, in this simulation process, the 10 m resolution DEM could not capture
such local elevations in a few meter widths, and thus the simulation results were
affected. Figure 6.24 represents the cross section at two different locations in
upstream and downstream, with different DEM resolutions.
Figure 6.25 represents the hydraulic water depth for DEMs with 5 and 10 m
resolutions. The hydraulic depth was compared with the results of 10 m reso-
lution DEM. Modeling of the 2008 flood event had a maximum discharge of
205 m 3 /s. The model indicated that maximum water depth and velocity in the
Ubaye River were approximately 2 m and 3 m/s, respectively. This corresponds
to the field measurement reports of the 2008 flood. As a consequence, it could be
concluded that 5 m resolution DEM shows a successful simulation and has the
best agreement with the observed recorded data.
As mentioned before, the second aim in this section was to compare resampling
techniques in changing DEM resolutions. The intention was to resample the low
resolution DEM to a high resolution and to compare the low resolution DEM
before and after resampling it with the original high resolution DEM.