Methodology - Response of Flood Events to Land Use and Climate Change - page 64

3.3 Adding Feature Surface to DEM
In flood modeling, the DEM must contain all relevant surface features that affect
the flow distribution of water, such as dykes. For this purpose, it was necessary to
integrate the man-made terrain in the DEM, including roads, dykes, and buildings,
and their respective values were obtained from the fieldwork and previous dat-
abases and research in the area. Two separate DEMs were produced: one for the
1957 flood event before reconstruction and the height increase of the dykes, and
one after the 1957 flood event when the government decided to increase the height
of the dyke by about 0.5 m. Road generalization was made in the form of primary,
secondary, service roads, and tracks, and heights of 0.5, 0.3, 0.2, and 1 m were
assigned to different kinds of roads respectively, based on the literature review
[ 11 ]. The building also added to DEM as solid blocks hinder the flow water as it
surpassed the building. Due to limited data, heights of approximately 3 m were
defined for all buildings.
3.4 RAS: Geometric Data
Both SOBEK and HEC-RAS models applied in the hydrodynamic simulation
sector need geometric data surface, roughness values, cross sections, hydrometric
data, and DEMs. To prepare the geometric input data, it was necessary to apply the
DEM of the river system in a grid format. The HEC-GeoRAS model was applied
to prepare all input data before starting flood simulation in both modeling. The
process of importing data into HEC-RAS model was done in HEC-GeoRAS
models as a set of ArcGIS tools. This extension allows users to create an HEC-
RAS import file which consists of geometric data such as banks, dykes, river, and
flow path from an existing DEM and complementary data sets.
The process to import data into SOBEK was twofold. First, the input data for
1D features such as rivers or channels had to be imported and, second, the 2D
features such as overland flow were added. The 1D features were defined using 1D
nodes within the flow model. These nodes were connected as a network using
straight line connectors called ''reaches''. The details are explained in sector
( Sect. 3.9.4 ).
3.5 Creating Cross Section Using HEC-GeoRAS Model
Cross section data were applied to determine the conveyance and storage of flow to
the channel and floodplain areas. Cross section must be obtained at sufficient
intervals and lengths to define the flow capacity of the river and its floodplain, at