Theoretical Background - Response of Flood Events to Land Use and Climate Change - page 12

Fig. 2.1 Comparison
between two terrains.
a Irregular DEM. b Gridded
DEM
The measures of shape most commonly used are slope and aspect of the down
slope direction [ 3 ].
According to Vaze et al. [ 1 ] and Teng et al. [ 4 ] DEM is used to derive some key
information which is important in distributed hydraulic and hydrological models;
such as flow paths; dispersion; and accumulation of water, terrain slope, drainage
networks, drainage divides, and catchment boundaries. Vaze et al. [ 1 ] also com-
pared the traditional methods of topographic maps, field surveys or photographic
interpretation with the application of DEMs. Vaze et al. [ 1 ] concluded that DEM is
an effective way to present ground surface and extract the hydrological features;
thus bringing advantages in terms of processing efficiency, cost effectiveness, and
accuracy assessment. Burrough and McDonnell [ 5 ] defined DEM as ''any digital
representation of the continuous variation of relief over space''. Wood [ 6 ] also
defined DEM as ''a computer representation of the earth's surface which is pro-
vided a base data set from those topographic parameters that can be digitally
generated''. Alternatively, the DEM could be used in mapping the possible loca-
tions of an endangered species whose habitat is altitude dependent. Here, the
resultant value for each grid cell may be either the elevation of the center point of
the grid cell or the average height of the area covered by the grid cell. The actual
characteristics of a grid can be adapted to suit its major application. For instance,
the application of the grid may require that all local high points (hills or moun-
tains) in the source data be retained in the grid. Technically, Olivera et al. [ 7 ] have
another definition for DEM; they defined DEM as an array of squared pixels or
cells with an elevation value specific to each pixel. They said that DEM is com-
monly used in automated drainage analysis methodologies due to its inherent
simplicity characteristics of the data structure. Point elevation information in DEM
which is a representation of the terrain, can be of two types—a. irregular and b.
gridded (Fig. 2.1 )[ 3 ]; a. An irregular spaced DEM is often interpreted as a
triangular irregular network (TIN). TIN represents a surface as a set of irregularly
located points linked to form a network of triangles with z-values stored at the
nodes.