SIG and space Imagery in the update of the hydrographic network of the catchment area of Chaabet el Ham and the aspect of pollution (Western Algeria)


BENTEKHICI - Nadjla
Division of the remonte sensing
National Centers of space technics CNTS
BP13, Arzew, Algérie
nadjla_b@yahoo.fr


ZEBBAR Zine - Eddine
Division of the remonte sensing
National Centers of space technics CNTS
BP13, Arzew, Algérie
zebbarz@hotmail.com

Summary:
The space imagery present of the strategic mines information that is for the decision makers or the researchers. The control of processing and interpretation of these data offer considerable possibilities in the exploitation of knowledge of the physical environment.

This work was elaborate in order to include/understand and to give an analysis on these methods of treatment making it possible to characterize the surface water run-off in a catchment area.

It is a question during this study of giving and of making a whole characterization of the hydrographic network of an area catchment by the use of a SIG. This characterization was carried out in an entirely automatic way, in order to carry a new technology to delimit the drained surfaces.

So the principal objective of the use of these new applications is the actualization of the hydrographic network as well as a delimitation of the surfaces to drain to expose to a contamination by worn water.

In the area of Ain Témouchent, among the basins slopes existing we chose that of wadi el maleh to base itself on under catchment area of Chaabet el ham and this for the following reasons:

It under catchment area is a receiving medium of urban worn water of the agglomeration of Chaabet el ham, waste water of the economic units social established in the industrial park of Ain Témouchent, and as well as the worn water rejected by the zone of activity of the commune of Chaabet el ham.

1 Introduction:
During these last years, the use of the SIG took a great importance in all the fields, this new technology to date became a tool of information of decision-making aid, it will give powerful results.

Space characterizations of a catchment area devrant to be automatic with an aim of obtaining drained correct results for the determination of the surfaces on the one hand and the space localization of the outlets of worn water on the other hand.

The latter became principal causes of contamination and surface water pollution, as well as the harmful effects which can be generated, especially that the problem of the water pollution starts to be posed in our country, owing to the fact that many communes are deprived of stations of purification of used water, thus involving the excessive contamination of surface and underground waters.

To this end, the use of this data base became as being a bottom for the cartography because of interest which it carries, it is very considerable for the actualization of the hydrographic network.

2 Objective of work:
It generally consists in working out an update of the hydrographic network knowing that this last presents the receiving medium of urban and industrial worn water.

It should be noted also that this study is based on the planimetric characteristics of the catchment area of interest, of which they are obtained starting from a geographical request. This work has a second shutter including understanding the positioning of the point of the waste water discharges as well as the generated impact.

3-Methodology of work:
The method used in the present study was based on the actualization of the hydrographic network as well as the automatic extraction of the parameters characterizing the catchment area from the point of view forms.
This methodology comprises a whole exposed flow chart appears n° 01 of it.


Fig n 01: Flow chart of the scheme of work


4-Determination of the pilot zone:
Under catchment area of Chaabet El ham is located at the center of the wilaya of Ain Témouchent, in the Western of Algeria, distant North of 465 km Algiers.
The Wadi Chaabet el Ham is an affluent of wadi el Maleh which crosses 4 communes (Ain Témouchent, Chentouf, Hammam Bou Hadjar, Chaabet el Ham).
It is located between longitudes (35°17' 22 '' and 35°16' 37' ' N), and latitudes (1° 9' 24' ' and 1°26' 17 '' W).


Fig n 02 : Localisation de la zone of stady

5-Data used:
The cartographic data hold a great place with each stage of this study. So we used the following data:
  • Topographic Charts with 1/25.000.
  • The image Landsat ETM+ of May 19, 2002.
  • Limage Landsat ETM+ of the 12-02-2002.
These data are treated and corrected geometrically according to projection UTM 30 N Datum (WGS 84) Fig n°3.


Fig n 03 : Image Landsat 05/07/2002

6-Digitalization of the hydrographic network starting from the topographic charts:

The classification of the rivers starting from the image raises difficulties for orders 1 and 2, for that we were brought to digitized the hairy hydrographic one starting from a topographic chart (1/25.000) which will be useful to us besides with his actualization.

7-Actualization of the hydrographic network starting from the images:
Actualization was done by superimposing the hairy hydrographic one, traced starting from the topographic chart de1960, on the Landsat image taken in 2002.
This will enable us to determine in a quasi automatic way a whole series of planimetric and morphometric criteria characterizing the catchment area.


Fig n 04: Superposition and actualization of the hydrographic network on image ETM+ of February 12, 2002

8-Extraction of the hydrographic network starting from a MNT:
The digital model of ground (MNT) is a digital representation in term of altitude, it makes it possible to provide information on topographic surface from where its particular interest is to carry out a model of ground.
The acquisition of the altimetric data was made starting from the level lines of the topographic chart to the 1/25.000.
Using the MNT, we delimited under area catchment in question of seeing fig n° 05.

Fig n 05: Extraction of the Hydrographic network starting from the MNT

9-Determination of the planimetric parameters of the catchment area:
The new techniques of geographical information facilitated the clothes industry of this study to us and where the automatic extraction of all the planimetric parameters became thereafter an operation of followed and of analysis of a catchment area.
The purpose of the use of the various parameters morphometric is the evaluation of the characteristics of the physical environment of a catchment area.

9-1 The perimeter and surface:
From a geographical request by the use of language SQL, the perimeter and the surface of the catchment area of Chaabet el ham were given according to table n° 01.


Tableau n 01: Automatic extraction of the parameters of the area catchment

9-2 Coefficient of form KF:
It is Calculé by the following formula
KF = bm/La
bm: the average width of the basin
La: length of the principal river
KF = 5.39/13
KF = 0.144

9-3 Coefficient of compactness:
It is a relationship between the perimeter of a catchment area and the circumference of a circle having the same surface and the same perimeter of the catchment area.
It is Calculé by the following formula:

Kc = 0.28 * P/S 1/2
Kc = 1.77
8-4 Rectangle is equivalent:
One compares the Area Catchment to a rectangle having the same perimeter, same surface and the same index of Kc, one obtains Table n° 02.
It is defined to compare the basins slopes between them, from the point of view their characteristics of flow.


Table n 02: Automatic extraction of parameters of the rectangle Équivalent (Language SQL)

The analysis of dimensions of the equivalent rectangle shows that the length is higher than the width, therefore one can say that it is a lengthened catchment area.


Fig n 06: Graph of the rectangle are equivalent

10-Characteristic of the hydrographic network:
The hydrographic network gathers a multitude of information which can be approached by enumerating the elementary characteristics relating to the its evolution.

11-1 The hierarchisation of a hydrographic network:
The structure of a hydrographic network consists in classifying this last according to a certain hierarchy, this hierarchisation amounts allotting a sequence number at each water court according to a coding.
In our study we used, for the hierarchisation of the network (see fig 7), the classification of HORTON (1945), which comprises two stages
  1. to allot to each segment of the network an order; any section without affluent is of order 1, any junction of identical segment of order gives a higher order,
  2. to organize the orders according to the length of the segments.


Fig n 07: Hierarchisation of the hydrographic network of the basin of Chaabet el Ham According to the classification of HORTON

11-2 Report/ratio of junction:
It represents the quotient of the number of the thalwegs of order (n) by that of the thalwegs of order (n+1) From an automatic extraction according to language SQL, one obtains table n° 3 .


Table n 03:Extraction of report/ratio of junction of the area catchment of Chaabet el ham the

11-3 Density of drainage:
It makes it possible to determine the hairy hydrographic one, and is used primarily within the framework of the studies of the risings.
The density of drainage is obtained by the relationship between the length of the rivers and surface of the catchment area.


Table n 04: Automatic extraction of the density of drainage of the area catchment of Chaabet el Ham


Fig n 08: density of drainage

12- The interest of the characteristics of the Area catchment in the study of the outlet of worn water:
Under catchment area of Chaabet El Ham represents the receiving medium of urban worn water of the agglomeration of Chaabet El Ham and its zone of activity as well as waste water of the industrial park of Ain Témouchent, and more exactly of the manufacturing unit of Enad-henkel detergents.

The use of the actualization of the hydrographic network enabled us to position the outlets of urban and industrial worn water on the basin in question.

We noted that the outlet of worn water of the agglomeration of Chaabet el Ham positions on one flowing of order 5 and the outlet of industrial water of the manufacturing unit of detergents positions on one flowing of order 3, this says more the order is high plus the streaming of the surface waters which forwards by the outlet for the period winter is significant.

As, with a density of drainage of 2.29, one can say as under basin in question is well drained, thus worsening his contamination by urban and industrial water.


Fig n 9: Outlet of worn urban and industrial water.

This contamination leads to harmful consequences on the environment in particular the vegetation, this is quite visible on the image of Landsat Etm+ by applying the standardized index of vegetation (NDVI).
We noted a vegetation of very low density or a flora almost died in the site of the receiving medium of worn water of the commune of Chaabet El Ham and the rejections industrial of detergent unit ENAD of manufacture to see fig n° 10.


Fig n 10: Index of vegetation NDVI of Image ETM+ of May 19, 2002 .

From the positioning of the outlet and the impact generated on the environment it is possible to identify the surfaces drained exposed with a contamination by the daily discharge of worn water and to possibly cure consequently it (see fig n°11). We considered the overall length of the rivers exposed to this degradation at approximately 33.18 km.


Fig n 11: Cartography drained surfaces exposed to a contamination starting from an image.

Conclusion:
In this study we could determine the contribution of the satellite imagery as bases cartographic in the update of the hydrographic network as well as the positioning of the outlet of urban and industrial worn water on under basin in question.
This leads us to determine the drained surfaces likely to be to contaminate by the daily rejection of the water used without any treatment the precondition and of a rather significant volume.

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