precipitations in spring and autumn, rarely snow-covered
cold winters.
The annual pluviometry varying between 350 and 400 mm
and a number of days of rain by year of 60 to 100 days. These
are in general rains of short and intense duration. The
vegetable shelter finds a handicap to its development because
of this weak duration of precipitations, as well as the
important sunlight that renders the capacity of ground
stocking very weak.
The occupation of the ground is varied and is composed
mainly of natural vegetation, reafforestation of pine of Alep,
cereals with fallow, culture under greenhouse, maraichage,
fruit trees, naked terrain, framework and carrieres. The
annual average temperature is in the order of 17 ?c.
Watershed are characterized by frequent winds rape with a
West- East direction .
3. METHODOLOGY
Each time an important rain comes across a given region of
the country, one expects floods. To apprehend these floods,
we will have to understand the cycle of the water and its
various interactions with a physical medium.
The determination of these floods for given frequencies by
limnigraphiques measures or by hydrologic models
simulation can inform us on the volume and the propagation
of flood. In practice we find ahead the problem of the
transformation of the debit in height in a transverse section
determined by topographic conditions.
With traditional data, the cartography of inondables zones
are determined and delimited by inquires in situ. It
represents information of overflows of the oueds that remain
vague, approximate with punctual information and not horo -
dated.
The present work aims to show a method of utilization of the
numerical cartography, numerical terrain models (M.N.T),
systems based on geographical information raster and the
transformation of data acquired by remote sensing in useful
data in the hydrologic modelling deterministe of conceptual
type, distributed and meshed and the transformation of
debits in height. The visualization of zones allocated by
floods has been made on the numerical model of the terrain
and the land occupation chart.
4. INTEGRATED DATA ANALYSIS
Several authors confirm the application of remote sensing
and geographical information system in the area of
predictions of floods and the cartography of floods.
The interest of the implementation of the Model
Hydrologique mesh in the framework of this work is taken in
to consideration by the spatio - temporal distribution of data
géocoded by discretisation in regular squared mesh. It
presents an analogy with the representation of data in a
system of geographical information matrix and remote
sensing data.
The hydrologic modelling employed used characteristics such
that the size of the mesh, the allocation of the ground, the
function of production and the function of transfer are, with
the M.N.T, the main factors to take into account and to
manipulate with intelligence and care. The flow chart here -
after (Fig.1) shows the principle of the hydrologic modelling
employed in the framework of this work by the superposition
of layers of information.
The area of G.I.S is in full expansion in our days, whose
heart is a database of digital and spatial reference. They are
considered as a computer system allowing from various
sources, to gather and organize, to manage, to analyze and to
combine, to elaborate and to present geographically
contributing localized information notably to manage the
space
LAND COVER ef stream
t
=
RAINFALL water
Fhw
emos
cR
Figure 1: the principle of the hydrologic modelling by the
superposition of layers of information.
For this work several software have been used to prepare the
physiographic and meteorological database necessary for the
simulation of a drawn to scale flow of a watershed. ( Idrisi;
Arc/Into, Hydrologic Model meshed)
4.1 Physiographic Data
The estimation of the physicals characteristic of watershed
has been undertaken from cartographic data ( topographic
map to 1/25000) and data acquised by remote sensing of the
satellite image Landsat TM of 15 March 1993 of the region
of arzew.
4.1.1 Numerical Model of the Terrain and layers derived:
A numerical model of the image terrain has been realized from
contour lines with a resolution 100x100 m . The choice of the
size of the mesh has been determined with the objective of our
work and for a large discretisation. The objective is to create a
value of altitude on each mesh.
The utilization of an M.N.T in a Hydrologic Model meshed
imposes the respect of a fundamental critera: It has to allow
the flow of water uphill the endorsement.(draining). To
remedy to this situation we have to process the minima -local
stemming of techniques of interpolation. The operation
92 Intemational Archives of Photogrammetry and Remote Sensing. Vol. XXXII, Part 7, Budapest, 1998
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