Parameters
Period of return (year) a(T) KT) c(T)
5 209.479 | 0.04362 0.6688
10 278.067 | 0.223 0.702
20 320.8 - 0.014 0.706
50 398.8 -0.007 0.729
100 396.4 0.431 0.757
Table 3: Parameters of adjustment of the law of Talbot
5. PREDICTION OF FLOOD AND CARTOGRAPHY
OF FLOOD FIELDS
For the determination of the debit of streams in the
application of the Meshed Hydrologic Model, we need the
combination of the function of production histogramme of
hydrologic classes distributed by isochrones and the
hyetogramme of rain.
In our study, transfer and production functions are estimated
by hierarchisation coefficients and speed logic of streams
(m/s) according to the cover of the ground and the slope ( see
table 4). The speed and the coefficient of streams are
important in the oueds where the necessity to show the river
(oued) class and that the estimation of these functions notices
an empirical knowledge based on the experience.
Coef of runoff Speed of runoff
classes | 0-10% | 10-25 |>25% | 0-10% | 10-25 |>25%
Build | 0.20 0.22 0.25 0.15 0.30 0.60
Crop |0.04 0.05 0.04 0.10 0.40 0.20
Forest | 0.02 0.03 0.04 0.80 0.16 0.30
Nude | 0.07 0.08 0.09 0.10 0.20 0.40
Oued | 0.80 0.90 1.00 1.00 1.20 1.60
Table 4: Parameters for production and transfer fonctions
Debits simulated for each period of retum 5, 10, 20, 50
years, and a step between isochrone of 15 minutes are
represented in the figure hereafter (Fig.2). The three first
curves correspond to the hyetogramms obtained by the
application of the method of Chicago with a peak placed to
25%, 50% and 75% of the duration of the shower. The
representation on a same time scale was processed by
convenience of presentation. Because of the lack of gauging
stations on the Oued El Mohgoun, we have not been able to
controle our model.
The simulated debit that arrives to the outlet has to be
transformed into height of water and compared to the ability
of pluvial water evacuation by the Oued El Mohgoun. In this
case , the lenght-profile for determination
of the slope of the Oued and the cross-profile in a section of
the Oued for the determination of the wet section, the wet
perimeter and height of water are demanded. The
superposition of the M.N.T and the hydrographic system ,
have allowed us to establish the profile in lenght and a
mission of terrain for the establishment of cross-profiles.
For the period of return of 100 years and the application of
the formula of Maning strickler, we have observed that the
Oued El mohgoun leaves its bed to flood the plain of the
straight bank and some illicit constructions of the left bank.
The calculated water height exceeded pulling it "le tirant".
12—1-
100-1
(m3/s)
DORIA
Time (Step by 15 mn)
Figure 2: Debits simulated for each period of return. 5, 10,
20, 50 years
of water 1,50 m. The visualization of zones allocated by
floods has been made on the D. T.M and the land cover to the
endorsement from the point of the measure. This zonage can
be confirmed by remote sensing cartography of inondables
zones and consequently a means of wedging of the model of
simulation. For the cartography of inondables zones, the use
of a classification and the type of the satellite will depend
on difficulties met for the immersed zone separation, humid ,
not, satellites characteristics touched (time of passage,
resolution, etc.) and the phase of flood.
The duration of transformation of water rising from flood to
inondation (overflow, stagnation, impact) is necessary for the
choice of the satellite imagery and its interpretation
6. Conclusion and perspectives
It is premature to present currently complete and definitive
results on the whole of the thematic. It appears that
following the conditions of the environnement and
especially the land cover by remote sensing of watershed can
help to define sensitive zones to the flood and important
regions to prepare for hydrologic purposes. This work will
constitute a link of a database on hydrologic parameters s of a
watershed.
The Urban Amenagement Master plan recently established
for the daira of Arzew will be able to constitute a land cover
of watershed to apprehend their impact on floods and
consequently extended to the affected zones.
Several necessary data for the hydrologic modelisation can
benefit from the contribution of remote sensing. Works are
94 Intemational Archives of Photogrammetry and Remote Sensing. Vol. XXXII, Part 7, Budapest, 1998
