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Contribution to the management of the sensitive spaces by the geographical information systems and remotesensing: the case of the basin of the Gharb (Morocco)

A.Amrani1, M. El Wartiti1, M. Zahraoui1, A. Calle2 and J-L. Casanova2

1 Laboratoire de géologie appliquée, Université Mohammed V, Rabat (Morocco).2 Dpto. de Física Aplicada. Universidad de Valladolid.

Resumen

Contribución de los sistemas de información geográfica y la teledetección a la gestión de espacios sensibles: el caso de la cuenta del Gharb (Marruecos)

El estudio de las limitaciones naturales en la depresión del Gharb y su costa, se basa en la in-tegración y el análisis numérico de los datos procedentes de múltiples fuentes y métodos con-vencionales clásicos de síntesis. El área de interés es una depresión asimétrica limitada por dosdominios estructurales importantes, en el sur de la Meseta y el Rif en el norte. El resultado de es-ta configuración es un área plana con cauces de ríos poco profundos. El clima es mediterráneo.Desde el punto de vista sismo-tectónico, el área de estudio es inactivo. Su parte central corres-ponde a zonas de sismicidad baja o antisísmico. La morfología, la contaminación del agua y elsuelo, cubierta vegetal y la explotación de canteras son las limitaciones que modelan la depre-sión Ghrab. La integración de todos los datos en un SIG desde múltiples fuentes de datos, se mues-tra como la herramienta más eficaz.

Palabras clave: Teledetección, SIG, Estudio geomorfológico, Gharb.

Abstract

The study of the natural constraints in the basin of the Gharb with his littoral is based on theintegration and the numeric analysis of the multisource data and a classical synthetically approach.The zone is a dissymmetric basin, limited by two great structural domains: Mesetan domain tothe South and Rifian domain to the North. It results from this configuration a flat zone with notvery deep stream beds. The climate is of Mediterranean type. From a seismic-tectonic, the studyzone is nether quiet central part corresponds to low seismic domains. The morphology, the pollutionof water and soils, the vegetation and the exploitation of the quarries are the main constraintsquestioning the management of the basin of the Ghrab. The integration of the whole multisourcedata in a GIS and remote sensing, seems the more efficient method in term of the time and for themanagement of the spatially referenced data.

Key words: Remote sensing, GIS, geomorphologic study, Gharb.

* Autor para la correspondencia: [email protected] Recibido: 04-07-12; Aceptado: 12-09-12.

Asociación Española de Teledetección Revista de Teledetección 38, 77-91ISSN: 1988-8740

Introduction

Any project of regional planning andurbanization, such as the installation of thegreat infrastructures and projects structuralaims the preparation a logic diagram making itpossible to act in various ways. The objectiveis to show the environmental values of the zonein question. In the case of the socio-economically active depression of Gharb andin order to understand its specif icities, wepropose in this work to def ine the currentphysical state characterizing its naturalenvironment. Within this framework will be tosupport the potentialities and the environ-mental constraints relating to the climate,ground, under-ground, geomorphology, waterresources and biodiversity. Their definitionswill be based on the combination of a digitalsurface updated analysis (thematic cards), so,will be drawn their interactions towards thegeomorphological, ecological and geologicalenvironment, the purpose of which is to definethe natural risks and their impact on the processof land settlement and the management of thesensitive spaces.

In this study, we shall become attached tothe development of the quantitative andqualitative modelling of the potentialities andthe physical constraints relating to any typesof process of land settlement of the Gharbplain. In this frame the subject of the environ-ment will have for objective to answer thequestion: Why the study of the natural risks ina territory so vulnerable in mid-term and long-term as the Gharb plain?

The Gharb plain aroused numerous geolo-gical, geomorphological studies (Michard,1976; Thauvin 1996; Zouhri et al. 2001, 2002;Kacimi, 2004) and pedological studies(Ormvag, 1994 and Resing, 1994). Because ofits extent and its agricultural profitability, thestudy of the constraints of development of thesensitive spaces, make that it is essential toresort to integration, in a SIG, of multi-sourcedata. The cartography of the physical elementssuch, the catchment area, water resources,vegetable cover, the seismic-tectonic andgrounds. This technique will make it possibleto specialize the zones easily flooded,vulnerable, no suitable, etc.

So we will be interested in the relationsbetween the natural constraints and theirimpacts on management of the territory of theplain. This one is given an important ecologicalinheritance diversif ied (littoral zone; plains;sites of biological and ecological interest(SIBE), forests, lakes, fertile grounds. Thisenvironment remains, in certain places, whichwe will delimit, fragile with very vulnerable.Their protection and safeguarding should bethe subject of the governmental and non-governmental, national and internationalinterventions.

Considering its environmental charac-teristic, the Gharb plain arouses a great interestof the various operators. The zone of Gharb isrichest (fertile grounds, water available, easyaccessibility, geographical proximity, beaches)in against part these assets are the subject of abad management by ignorance (dewatering,water pollution, ground and ecology) theseimpacts constitute a permanent natural risk(risk of flood, impoverishment of the littoralzone). The protection and the safeguarding ofthe natural resources are real concerns. Theanalysis and the discussions below will be aprelude to the principal recommendations tofollow for a good control of our territory.

These will allow us to begin a thematicdiscussion explaining the main questions, theobjective of which is to facilitate, to the socio-economic operators, the understanding of thephysical characteristics, their potentialities andtheir constraints, so recommendation and themeasures to be taken.

Area of study

The Gharb plain is a Flat zone and directlyopen on the Atlantic Ocean. It is limited to theNorth by the first deformations of the chain, tothe East by the basin of Saïs and the f irstmountainous reliefs of the Middle Atlas, to theSouth by central Morocco and to the West bythe Atlantic Ocean. The perimeter of thestudied area occupies the Northwestern centerof Morocco and the Western part of basin ofSebou. The average altitude varies between 0m and 200 m. These features are summarizedin the figure 1.

78 A. Amrani, et al. / Revista de Teledetección (2012) 38, 77-91

Materials and methods

The use of satellite remote sensing as a toolfor control, management and development ofthe natural environment, has become in-creasingly necessary for preventive risk studiesand studies of spatial planning. As such,satellite imagery could provide relevantinformation on the direct and indirect land inquestion. Indeed, these images, provided byonboard sensors by satellites, constantlybecoming more eff icient, in terms spectralresolution, spatial, radiometric and temporal.

In the present work, we will use only thegeneration of images TM and ETM + (EnhancedThematic Mapper plus), whose acquisition of

Landsat data globally, medium resolution (30 mresolution). This mission has gained a wealth ofdata on the terrestrial and monitoring of naturalphenomenal changes and/or man. Given theirspatial and temporal resolution, the sensor TMand ETM + images to provide a medium scale.

This study is largely based on photointerpretation, computer, digital spatial data in2D (spatial and temporal analysis of satelliteimages Landsat TM and ETM +, topographicmaps at 1/100 000 and others) and a classicalsynthetic approach (literature and controls theland). The data set is integrated into aGeographic Information System (GIS).

The purpose of this work will be to definethe environmental potentialities and cons-traints, having direct and indirect impacts onthe integrated installation in the sensitive areas.The def inition of the potentialities and theconstraints will be based on a space analysis ofthe geoinformation. In front of the multitudeand the diversity of information, a data base tospace reference (BDRS) will be developed, andwill allow the integration of the whole of in-formation in a SIG, whose paramount objectiveis to delimit the sensitive surfaces, accordingto degrees’ of vulnerabilities.

This study is based on photo interpretation,computer-aided data numerical spatial two-dimensional 2D (topographical maps, satelliteimages Landsat TM and ETM + (spatialresolution 30 m), drainage, Google Earthimages and a classical synthetic approach(field observation and review of the literature).the data set is integrated into a GeographicInformation System (GIS). structures of spatialinformation, the study area, are treatedaccording to the nature of objects (point, line,polygon, raster). storage and management ofall has been made by well-defined topologies.modelling mainly concerns computer datastructures, geo-referenced.

The adopted SIG results from the data basemanagement system to space reference(SGBDRS). It will make it possible to managethe data base geo-referred (BDGR). This purelydata-processing application enabled us tointegrate, in the SIG, the various geographicalstructures. these structures of space informationare introduced into an Euclidean space, byrespecting the type of object (specific, linear,

Contribution to the management of the sensitive spaces by the geographical... 79

Figure 1. Geographical situation map of the Gharbbasin.

Figure 1’. Image google-maps (2012) Gharb Basin(visible channel).

polygonal, matrix). The storage and themanagement of the unit will be done accordingto well defined topologies’of the data-processinglayers (integration, superposition, inclusion,crossing). It is about a simple operation,managed by the SIG and will allow extractingthematic cards while synthesizing the differentinformation (potentialities and constraints)

The elaborated cards represent the physicalelements of the depression. The superpositionof the whole of space data in a SIG is anoperation of integration and treatment of thegeoinformation. In this work, we will approachthe SIG to specify its interest on the data basemanagement to space references like toolcarrying the information, which will facilitatethe good control of the factors such, the slopes,morphology, the seismic-tectonics, lithology,the hydrographical network, cover vegetableand the grounds, of which the goal is thedefinition of their impacts on the process ofadjustment of vulnerable spaces.

Results

A monotonous morphology

The Gharb plain, located at the Northerncenter of the country, is a flat area with excesswinter rainfall it is confronted with the risks offlood and tsunamis the plain is particularizedby its proximity at the Atlantic coasts and byits flat topography. This morphologicalconfiguration constitutes a constraint for theGharb plain management. Its morphometricstructure results from the tertiary tectonicphase which is characterized by the genesis ofa Riffian mountainous complex in the Northand the basin of Gharb in the South (ElGharbaoui, 1987). the analysis of themorphometric data enabled us to formulate thefollowing reports:

— The slopes are, as a whole central andlittoral, weak and remain ranging between 0 to4%. The weak slopes, lower than 2% arelocated primarily near the mouth of the SebouWadi, where the exaggerated shapes ofmeanders are conf igured (very weak slopesdeveloping exaggerated sinusoidal forms, inthe East of Kenitra). These localities constitute

a zone of permanent risks of flood. Theirmanagements remain expensive.

— The beds of the Sebou wadi and itseffluents lose their widths of the downstreamupstream. The direction general of the surfaceflows of water respects the direction general ofslope, is (upstream) towards the West(downstream). In order to ensure perenniality,especially qualitative of the surface waterresources of the littoral zone (downstream), theprotection of the upstream remains stronglyrecommended. This one could be done via theinstallation of several hydraulic points ensuringthe regularization of level of water at the timeof risings.

— The visual quality of the environmentlandscape is quite ventilated. The projects ofinstallations taking into account the environ-mental concern could only improve the touristpotentialities of the littoral zone, especially thebeach of Sidi Boughaba and Moulay Bousel-ham. The adjustment of these places of interest,according to standards’ in force, will havesocio-economic and environmental repercus-sions of a great scale as well on a regional scale.

Rich and quite ventilated landscape

The analysis of the landscape is particularlyimportant, when a process of construction ofan urban infrastructure projects the realizationof multiple potentially aggressive actionstowards the environment. For this reason, it isnecessary to divide, the zone in under zones orremarkable landscape sites, more or lesshomogeneous, allowing the study of degree ofvulnerability, land uses, morphoterritorialcharacteristic, geological, etc.

If one puts at with dimensions someelements constituting the landscape such, therivers, the agglomerations and the disperseddwellings, one can then subdivide the zone ofstudy into three sub-units:

— Northern landscaped unit: characterizedby a flat morphology lined with fossil dunesand drained by large wadis of the catchmentarea of Sebou. it concerns the central andcentro-western part of the plain. The landscapeof this zone has an important value, not onlyby its own intrinsic value, but also, by the fact


that it constitutes a zone of strong agriculturalpotential on a very fertile territory but alsosensitive.

— Southernmost landscape Unit: It is a flatareas mainly Covered by the forest ofMaâmora. The two units are separated by theSebou wadi;

— Western littoral Unit: this zone ischaracterized by a series of consolidated dunecords, forming sub parallel bands with thecurrent coastal shore. This littoral area knowscurrently over-exploitation of the careers. Thisanarchistic exploitation, Hinder any action oflittoral area planning. It became vulnerablearea. Anticipation in term of planning of thesevulnerable area, along the coast, will create avery important economic activity, whilebenefitting from visual quality from the coastalenvironment and its natural attractively.

There are other components which appear inthe plain such, the rivers and the plantations,as well as specific elements like the careers andirrigated agricultural areas. These elementswill be the subject of a study in the nextparagraphs.

A regional geology of alpine type

A lithostratigraphy characterizing a basin of subsidence

The filling of the Gharb plain was completedby the formation of a vast alluvial plaincorresponding to two banks of the Sebou wadi.Its evolution during Cenozoic involved thegenesis of a vast flat plain with reliefs verylittle developed. In North, are located the firstdeformations of the Riffian chain, it is aboutpre-Riff ian formation raised brutally inoverthrust nappes directed NE-SW (Monitin,1963). The whole of the basin knew asubsidence since average Vindobonien. Itscollapse persisted since the Quaternary untiltoday (Comb, 1975; Cirac, 1985).

Active tectonics

As for the sector of study, the Palaeozoicbase is plunged South towards North, under the

Neocene cover and Pleistocene of Gharb by aseries of steps constituted by faulted and tippedpanels towards the NNW (Cirac, 1985 andFlinch, 1993). The genesis and the structuralframework of the basin of Gharb are mainlyconditioned by the evolution of the Riffainchain (alpine orogenesis). Studies of seismic(Flinch, 1993; Flinch and Vail, 1998 and Littoand Al, 2001) showed that the material of thesupra-tablecloth is affected by faults of variousorders.

During the Quaternary one, the Gharb basinhas sudden vertical movements in response tothe neotectonic phase of alpine orogenesis(Michard, 1976; Aberkan, 1986; Piqué andMichard, 1987 and Zouhri et al., 2002). Theseneotectonic movements are induced by normalfaults. The structure of the basin is controlledby Hercynian faults materialized by two greatdirections NE-SW and NW-SE. They control-led the paleogeographic evolution of the basin(Zouhri et al., 2002).

A plain with strong pedological potential

In spite of its agricultural potentialities, thepedological studies are rather numerous(Aubert, 1950; Ormvag 1994; Resing, 1994).These studies enabled us to understand the pe-dological characteristics, to set up pedologicalmap and to know their morphological andanalytical characteristics. The studies ofOrmvag (1994) showed the existence of 6 greatgroups of grounds described below (figure 2,chart of the pedological units).

— Soils of the type B or browned soils:These are soil that one finds in the perimeterof Maâmora and the northern zone of theforest. it is about sandy and washed soils,developed on the argillaceous areas. Thethickness of the sandy surface layer exceeds2m and presents a brownish coloring;

— Soils of the type C or Calcimagnésicsoils: it is about the soils characterizing thenorth-eastern zone. They present a carbonatedcomposition (calcium and magnesium) and areregarded as carbonated soils;

— Soils of the type H or hydromorphic sols:They concentrate in the depressions and theedges of the merges. Those present the


character of old hydromorphie. They are fairlyorganic sols.

— Soils of the types P or podzolic sols:They are along Sebou wadi and its affluents, inthe low zone. They are characterized by anincompletely broken up humus and ofgranulous structure. They have a rusts colorcaused by iron oxides, with tendency ofconcretion formation.

— Soils of the type X or sols with ses-quioxides: These soils present a black color.They cover the relatively low zones and aredeveloped on argillaceous alluvia of depres-sions. They have texture of an argillaceous typeof low permeability.

— Soils of the type V or vertisols: It isabout very fertile soils located on both sidesvalley of Sebou. They are soils with roundedand angular structure

The various identif ied and described soilsare essential for maximum agricultural pro-duction: cereal, fruit groves, leguminous,industrial crops, market gardenings and foddercrops. These soils support an agriculturalproduction, dominated by cereal. It covers themain regional and national needs. Other

agricultural activities constitute also animportant source of incomes. In spite of, theclimatic variations which occur, since abouttwenty years, by a greater irregularity of rains,the problem of drought does not arise since thezone has an important underground source(tablecloth of Gharb).

Available water resources

Under ground waters: An important tablewater threatened by pollution

The zone of study has a large Water-tablesurmounted locally by several semipermeablelenses. The geological and hydrogeologicstudies qualified these lenses as perched watertable (Thauvin, 1996 and Resing, 1994). Theirextensions can reach tens of square kilometers,their powers could exceed a few meters(figure 3 water map). They are related to thetopography of red clays and to the thicknessof the sand which surmount them (Kacimi,2004). Their hydrodynamism is essentially


Figure 2. Schematical map of the pedological units recognized in the studied zone (from the “Atlas of the Gharb”,modified).

laminar, with a karstic circulation in thecoastal zone.

From the environmental point of view, theGharb Water-table is directly threatened by theliquid infiltrations (pesticides, fertilizers,industrial waste…). The Permeability of theSurface and The vertical faults affecting thecover accelerate the risks of pollution of the tablewater.

Abundant and polluted surface waters

In this part, we shall develop the hydro-logical study to release the qualitative andquantitative aspects of surface waters (O.Sebou, dayas, lakes), while giving a detailedattention to the hydrographical networkHowever, the principal objective of this studyis to evaluate and develop the surface waterresources (figure 3, map of water resources).

The analysis of the water resources map of thezone of study shows, the presence of ahydrographical network little developed,characterized by its exaggerated forms ofmeanders and its general orientation towards thewest and the WSW. The principal wadi is Oued

Sebou, it constitutes one of the principal sourcesof surface water. The river of Sebou and itssecondary affluents such, Ourgha Wadi and Behtfollow directions imposed by the flat morphologyof the crossed zone, with a permanent flow.

A morphologically easily flooded depression

The morphometric analysis of the catchmentarea of Sebou shows, that the Sebou wadi flowsin a relatively boxed bed wich is not very deep atits upstream part. It widens and is raised in itsdownstream part wich is relatively flat. Moreover,the catchment area of Sebou is subjected to apluvial regime and the highest debits result fromthe Ouergha wadi. In 1963, occurred the strongestfloods known in the basin of Sebou . In 1996, thezone knew other series of floods which involvedimportant damage in the town of Kénitra(national Report on the prevention of the di-sasters, floods of the Gharb plain 1996). Figure 4shows the easily flooded and vulnerable zones.

According to the analysis of this map, thedelimitation of the zones of risks of floodsshows that the town of Kenitra and its peripheryare permanently exposed with the phenomena


Figure 3. Map of the superf icial and underground water resources, extracted from the topographical maps,hydrogeological maps of the Gharb basin and from (manually the Atlas of the Gharb).

of the floods. The installation of importantinfrastructure, (industrial park, residentialzone, airport…), far from Sebou wadi,principal source of floods, will ensure aneffective planning of this area. Within thisframework and in order to minimize the risksof floods, the three large wadis: Sebou, Behtand Ouergha, principal sources of floods, areregularized by important hydraulic installationsor dams, which were realized for the protectionof the plain against the risks.

Quarries exploitation: an excessivelyexploited richness

Along the littoral zone, between (Kenitraand Moulay Bouselham), the majority ofquarries are abandoned, without any re-mediation of the exploited sites (figure 5). Themajority of the owners do not respect theirCPS, especially, during the extraction (use ofthe high quantities of the mines, over-ex-ploitation).

Conscious of the negative impact of thequarries badly managed on the environment,the persons in charge became exigent in term

of opening of new quarries. Everybody isconscious of the importance of the natural area(landscape, agricultural zone, green space).But, in the practice hundreds of hectaresdisappear for the benefit of the urbanizationand the installation of infrastructures: resi-dential zones, industrial parks, freeway.

To limit these threats, the littoral of Gharbshould be the subject of the urgent inter-ventions of a preventive nature. Its levellingand its valorisation require the integration ofleisure spaces such, the beach of MoulayBouslham and Sidi Boughaba in the goodgovernorship of the regional planning. Othervirgin spaces locating enter the two greatabove-mentioned sites should be the subject ofanticipatory installation against any kind ofpollution. This could improve the attractivityand territorial competitiveness in term ofurbanization, investment and tourism

A rich but vulnerable ecological environment

The zone of study includes the potential areawhich can undergo the impact of the activities


Figure 4. Vulnerability map and zoning of flooding risk.

of the industrial facilities. It has potential sitesconstituting a natural environment of greatecological and biological interest, as well at theregional level as national, such, Merja zerga,merja Halloufa, merja Bokka, Fourat and SidiBoughaba (f igure 8). These ecological sites(SIBE) are considered, on the biological level,as one of the crossroads of fauna, ensuring aconsiderable natural balance. Its potentialbiodiversity is exceptionally high compared tothe other natural sites of Morocco. Indeed, onecan only insist on the floristic, faunistic andlandscape richness during programming of anytype of project having environmental impacts.The center of the area of study is practicallyempty or contains isolated green points. TheMain species recognized in Gharb forest are:cork oak, holm oak, Thuya, Eucalyptus,conifer, mixed forests and matorrals.

The choice of color composites in the visibleand infrared is well justif ied and wanted tosurface mapping of the study area. The selectedbands have several technical advantages(spectral resolution suitable for mapping of soiland vegetation). As such:

The blue band is only sensitive to wave-lengths between 0.45 and 0.52 microns, de-

f ined in the visible. It also allows the dif-ferentiation soil-plant (Scanvic, 1993). Solarreflectance is maximum because of its shortwavelength (λ);

Also according Scanvic (1993), the greenband is an indicator of vegetation chlorophyllprimary and secondary elements of heavymetal content. The correlation between the blueand green allows discrimination of dissolvedorganic matter. This band is sensitive to thespectrum ranging from 0.52 to 0.60 microns;

The red band is very useful in the visiblespectrum for determining the limits of soil andland geological (lithological differentiation). Thespectral signature of this wavelength (0.63-0.69microns) provides a very high contrastlithological, with lower atmospheric disturbancesfrom other visible wavelengths. It also serves asthe structural analysis and plant classification;

The band near infrared (NIR) is useful formapping vegetation stress resulting fromgeological and iron oxides (Scanvic, 1993). Itscombination with band 3 allows the delineationof water bodies. The ratio of bands 3 and 4allows to differentiate biomass and vegetationmoisture. But, in situations where the vege-tation is in early growth and in an arid or


Figure 5. Situation map of the extraction sites of the building materials.


semiarid, this differentiation becomes quitetricky and the spectral signature is muchinfluenced by the signal from the ground, thiscould be possible disruption corrected(Escadafal and Huete, 1991).

Mapping the land of the study area isdeveloped at a medium scale 1/200 000. Theimages TM and Landsat ETM + is a basicbackground including the optimal combinationof colour in the visible red and near infraredFCC 321 and FCC 432 (false colourcomposite) for the analysis of land use andspatial distribution canopy.

The Satellite imagery and TM Landsat ETM+ used are supplied with a level of radiometricand geometric correction detailed by thesupplier. The choice of these scenes TM andETM + (taken as a multiple dates, 15/04/1985,12/09/1987 on the 20/08/1999, 23/08/2009 and16/10/2010), but we will use the two scenes(15.04.1985 and 20.04.2010 of the coloredcomposition FCC 432). This variety made basedon multiple calendars climate zone (spring,summer and winter) to view the land and theirbusiness in different states (soil covered byvegetation, bare soil, no clouds, moist soil, etc.).

Combining FCC 432 is used for land covermapping of the study area, knowing that it isan agricultural area with high potential. In thewestern part of the study area, the ground iscovered, almost entirely, a canopy largelyagricultural character (concentration ofagricultural activities along the coast of linen

depression Gharb to a depth of over 500 m ofshoreline). This false-color composition allowsthe detection and differentiation of thevegetative study area.

432 tri-color image on the FCC vegetationis easily recognized by its own spectralsignature in red with a maximum reflectancein the red and near infrared.432 FCC on thisimage, vegetation is easily recognized by itsown spectral signature. For example, the redcolour indicates the presence of vegetation(maximum reflectance in the red and nearinfrared (Scanvic, 1993).

The analysis shows that the two images inthe red and near-infrared (NIR) ranges are redcanopy dominant, especially in the westernpart of the study area. This can be explainedby the sustainability of water resources of theGharb basin (see paragraph 5: Water resourcesavailable) and soil fertility. In the study area,is one of the largest groundwater reservoirs(groundwater Gharb). The difference betweenthe two images, may be felt towards the EastMediterranean, whose terrain and theremoteness of the water are their effects.

Still, the analysis of satellite imagery andTM Landsat ETM + (432 BCF and 321 BCF,Figure 6 and 7), the study area especially thiscoastal landscape units, characterized by arelatively flat morphology surrounded by dunesand fossil drained by the major wadiswatershed Sebu. The landscape of this area hassignificant value in that it is an area with high

Figure 6. Comparative Images of reflection and absorption of EM radiation uneven depending on the wavelengthof the tri-color picture composed of channel 4, 3 and 2 false-color, left the scene of 20/04/2010 and right stageof 15/04/1985.

agricultural potential (fertile land), but alsosensitive. As we saw earlier, the evolution ofthe basin during the Cenozoic has driven thegenesis of a vast flat plain resulting from theaccumulation of a large sedimentary mass(which in some places exceeds 2000 m).Morphologically, said depression (Gharbbasin) is in the form of a basin that receives thebulk sedimentary all comers. It’s a wide openmiddle of the Atlantic Ocean, its intrinsic

characteristics reinforce and promote theagricultural potential of the Gharb plain byclimatic conditions.

Synthesis and recommendations

The analysis of the environmental elements(potentialities and constraints), it proves to beclear that the stakes of adjustment of the


Figure 7. Comparative Images of reflection and absorption of EM radiation uneven depending on thewavelengthof the tri-color picture composed of channel 3, 2 and 1 in the visible, left the scene of 20/04/2010 and right stageof 15/04/1985.

Figure 8. Map of the distribution of the vegetation (from the Atlas of the Gharb, modified).

depression of Gharb are important. The surfaceof study and rich in natural resources, they evenconstitute a constraint in a natural way or by abad governorship. So all the actors, on aregional and national scale, must become awareof this reality. It is necessary that the policy ofthe regional planning integrates theenvironmental constraints in all its strategy ofmanagement of the territory. This could bedone only by official will for the respect andthe application of Laws and Regulations.Elements below recapitulate the mainrecommendations to be considered in:

Regional seismic-tectonic risks

The establishment of the map of theintensities observed, since 1901 until 2001, wasfacilitated thanks to the available data of thedepartment of Physique of the Earth of theScientific Institute (figure 9). The analysis ofthese seismic-tectonic data, shows that the zoneof study is rather calm. It is in prolongation SWof the Rif chain. In addition, the zone inquestion is exposed to a certain tectonicactivity qualif ied as neotectonic, recent

tectonic activity of quaternary age, caused byshocks affecting the basin of Gharb. For thispurpose, the last earthquake, which hasoccurred on June 28, 2001 of magnitude 5 onthe Richter scale, reflects an important regionalsismotectonic dynamism. The definition of theparaseismic standards is strongly recom-mended and this, according to the standards ofparaseismic code RPS2000.

Strongly exploited water resources

The water resources remain quite sufficientcompared to the soil potentialities which ispedologically ready to receive the irrigation.In addition to this strong potential of perennialirrigation, there are also important poten-tialities in seasonal irrigation. Indeed, sinceabout twenty years, climatic variations occurby a greater irregularity of the rains and anextent, more and more, important of the areaof study. This deterioration is amplified by thebad management of the water resources thisinduces degradations on the level of thephysical environment, natural vegetation andquality of water. The good management of


Figure 9. Map of the deforestation zones and weak zones.

these not renewable resources requires a crucialreflection during the realization of any project.While benef itting from the great wotkconcerning the depollution of the Sebou Wadiand from the strategic and convenientprogramming.

Permanent risks of floods and the tsunamis

The flat morphological configuration of theGharb plain has at the same time an asset and aconstraint as regards management of thedownstream areas. With this flat configurationand the hydrographical network, the risk offloods and tsunamis is real. Because of thesignif icant absence of reliefs protecting thehinterland, the littoral zone is directly threatenedby the risks of tsunamis. Moreover, the Sebouwadi threatens the whole western territory suchSidi Allal Tazi’s urban area and Kenitra. In spiteof, the establishment of several upstreamhydraulic constructions. The flood risk ofdownstream area persists after each importantdownpour. So the department of the environmentof the Ministry of Land planning, Water and

Environment classif ied the urban centre ofKenitra as area of average risk. Its protectioncould be done only via dams of stabilization.

Safeguarding of the ecologicalenvironment

The negative impacts of engineering cons-tructions, on the natural and landscape environ-ment are taken into account, on the level of theimpact study on the environment of the variousprojects. Located in a subhumide bioclimaticstage, the Gharb plain is particularly sensitiveto deforestation especially in the forest ofMaâmora (figure 10). The studies of vulnera-bilities carried out within this framework,highlighted the multiplicity and the extent ofthe factors which go against the perennialityand against the variety of this not easily rene-wable capital. Among these factors, one quotes:the overgrazing, cutting of wood, absence ofregeneration of the forest. The analysis of thesefactors of degradation, show clearly that thesocial pressure constitutes a factor determiningof the deforestation of the forest of Maâmora.The consequences that will result from it are:


Figure 10. The sismotectonical activity map of the coastal zone of the Gharb, (Ait Brahim, 2003, modified).

natural environmental pollution, Sanding up,economic cost, rural migration.

Littoral: potential area to protect

In spite of, its great landscape and of coursetourist interest, the littoral zone, which extendsbetween Kénitra and Larache, is stronglyexploited and weakened by the extraction ofbuilding materials (f igure 10). This over-exploitation caused real attacks with thisfragile littoral environment (salinisation,pollution of the ground water of Gharb,disfiguration of the landscape).

In order to find the effective means for thesafeguard of this non renewable naturalresource, the state must directly intervene, inan urgent way, supported by the civil company,to oblige the owners to respect the terms of theimpact study on the environment. For thepolitical durability of the land planning, thisarticle should constitute the object of thedeepened researches undertaken by thedepartments, the concerned institutes and theresearchers, whose objective is to moreunderstand the characteristics of this naturallyrich area, but vulnerable and very sensitive, andto induce the positive impacts, by limiting andtreating those negative, if the control strategyof the programmed actions are taken intoaccount in a suitable way.

Conclusions

The study suggested here, makes it possibleto understand the importance of the use of theSIG in the studies of the Gharb plain planning.In addition, the discussions started in this studymade it possible to contribute to the com-prehension and the assimilation of charac-teristics of these potentialities and naturaland/or anthropic constraints. For this purpose,certain conclusions were drawn:

— Morphology, water, vegetable cover andthe exploitation of the quarries along the littoralzone are the principal constraints leading to aninstability of the natural environment.

— From point of view seismic-tectonic, thezone of Gharb is relatively stable. It supports

the construction of any kind of infrastructure,while respecting the standards paraseismiccode RS2000.

— Except some isolated areas, the, notprotected and badly managed, littoral like theindustrial zone, is an unfavorable zone for theinstallation of an important infrastructure. Theinstallation of such industrial constructions,will require a preventive strategy against thepossible risks of the tsunamis and the re-mediation of the exploited sites

— The choice of the adequate sites for theinstallation of the great projects, should be thesubject of a multidisciplinary decision.

— The integration of the whole of themulti-source data in a SIG, seems moreeffective in term of the management of the timeand the data base.

Generally, this study enabled us to reveal theproblems of the Gharb plain planning and theimportance of the method applied in the zoneof Gharb. In addition, this work made itpossible to establish a synthetic data base. Thisone intervenes at the same time upstream in thecharacterization of risks and constraints (objectof the research topic) and downstream likeDecision Support for the planning of the areaof study (objective of the research topic)

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