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Table des matières
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1
Liste des participants
2 Liste des principales institutions de
recherche fondamentale travaillant sur les problèmes liés à la
gestion des terres arides en Afrique occidentale
3 Assessment of geomorphological problems in
urban areas of drylands
4 Recherches de l'lnstitut de géographie de
l'Université de Hambourg (République fédérale d'Allemagne)
5 Université de Rouen (France). Laboratoire
de géographie du développement des régions arides (zones
tropicales et subtropicales). Études sahéliennes. Histoire et
thèmes d'une recherche.
Baldy, Charles. Agronome, Institutnational de la recherche agronomique (Bio clima), 84140 Montfavert (France).
Bonkoungou, Edouard. Botaniste, CNRST, B. P. 7047, Ouagadougou (Haute-Volta).
Claude, Jacques. Hydrologue, Centre ORSTOM, B.P. 182, Ouagadougou (Haute-Volta).
Cooke, Ronald. Professeur de géographie physique, Department of Geography, University College, 26 Bedford Way, London WC1H, OAP (Royaume-Uni).
Coulibaly, Lassina. CILSS, B.P. 7049, Ouagadougou (Haute-Volta).
Diagne, Papa Syr. Géographe, Institut du Sahel, B.P. 1530, Bamako (MaIi).
Diallo, Moulaye. Docteur vétérinaire, CILSS, Ouagadougou (HauteVolta).
Dresch, Jean. Professeur honoraire à l'Université de Paris-VII, Institut de géographie, 191, rue Saint-Jacques, 75005 Paris (France).
Fauk, Roger. Inspecteur général de l'ORSTOM, 24, rue Bayard, 75008 Paris (France).
Gallais, Jean. Professeur à l'Université de Haute-Normandie, Laboratoire de géographie du développement des régions arides, 76130 Mont-Saint-Aignan (France).
Gaymon, W. E. Chef adjoint, Bureau régional, UNSO, B.P. 366, Ouagadougou (Haute-Volta).
Gérard, Philippe-Auguste. Représentant du résident, FAO, Ouagadougou (Haute-Volta).
Guenda, W. Hydrobiologiste, Université de Ouagadougou (HauteVolta).
Kabala, Matuka. Ecologiste vétérinaire, Unesco-BREDA, Dakar (Sénégal).
Kambou, Sié Adolphe. Géographe, CNRST, B.P. 7047, Ouagadougou (Haute-Volta).
Lake, Louis-Albert. Géographe, IFAN, B.P. 206, Dakar (Sénégal).
Mainguet, Michèle. Professeur, Laboratoire de géographie zonale, Université de Reims, 57, rue P.-Taittinger, 51100 Reims (France). Reims (France).
Odingo, Richard. Professor-Senior, Programme Officer, UNU, Tokyo (Japon).
Ouedraogo, Marie-Michèle. Chef du Département de géographie, Université de Ouagadougou, B.P. 7021, Ouagadougou ((Haute-Volta ).
Ould, Cheikh Abdel Wedoud. Sociologue, Institut mauritanien de recherche scientifique, B.P. 196, Nouakchott (Mauritanie).
Pelissier, Paul. Professeur à l'Université de Paris-X, Université de Paris-X, 200, avenue de la République, 92001 Nanterre (France).
Roy, Jacqueline. Directrice, Institut des sciences de l'environnement, Université de Dakar (Sénegal).
Samake, Cyr. Senio Program Officer, UNSO, Ouagadougou (HauteVolta).
Savadogo, André. CILSS, B.P. 7049, Ouagadougou (Haute-Volta).
Sidikou, Harouna-Hamidou. Maître-assistant de géographie, docteur d'Etat, Université de Niamey, B.P. 418, Niamey (Niger).
Tall, Bye Mass. Ingénieur forestier, Forestry Department, Yundum ( Gambie).
Traore, Mamadou. Géographe, Directeur général de l'Ecole normale supérieure, B.P. 241, Bamako (Mali).
Toupet, Charles. Professeur, Université Jean-Moulin, Lyon-III, 47, rue Pasteur, 69224 Lyon.
Haute-VoIta (Ouagadougou)
Centre national de la recherche scientifique et technique
(CNRST). Comprend trois départements: Sciences humaines et
sociales; Sciences naturelles et écologiques; Sciences exactes.
Département de géographie de l'université.
Institut supérieur polytechnique: Agronomie: Élevage;
Forestrie.
Centre de l'office de la recherche scientifique et technique
outre-mer (ORSTOM). Géographie; Sociologie; Hydrologie;
Botanique.
Mali (Bamako)
Institut d'études rurales (études générales pour les
programmes de développement).
Ecole normale supérieure Itravaux de recherche en fin de
scolarité).
Centre international pour l'élevage africain (CIPEA-ILCA)
[études socio-économiques, agrostologie, santé animale].
Mission ORSTOM (hydrologie).
Institut du Sahel (dépendant du CILSS).
Mauritanie (Nouakchott)
Institut mauritanien de recherche scientifique (IMRS). EthnologieSociologie; Archéologie-Histoire; Préhistoire; Manuscrits arabes; Linguistiques; Traditions orales.
Niger (Niamey)
Département de géographie de l'université.
Institut national de recherche agronomique (INRAM).
Institut supérieur polytechnique (ISP).
Office national de l'énergie solaire (ONERSOL).
Centre d'agrohydrologie et d'agrométéorologie (AGRIMET)
dépendant du CILSS.
Sénégal (Dakar)
Département de géographie de l'université: programme
Télédétection; Cartographie au Sénégal; Recherches
climatiques.
Institut d'étude de l'environnement de la Faculté des sciences
de l'université.
Institut fondamental d'Afrique noire. Quatorze laboratoires dont:
Botanique; Géographie; Géologie.
Institut africain pour le développement économique et de
planification ( IDEP).
Ecole inter-africaine des sciences et médecine vétérinaire
dépendant de l'OUA.
Centre ORSTOM. Pédologie; Agronomie; Hydrologie; Géographie.
N B. Il n'est pas possible de répertorier correctement les centres de recherche appliquée établis sur des programmes précis et àcourt terme.
3 Assessment of geomorphological problems in urban areas of drylands
Ronald Cooke, Bedford College, University of London (United Kingdom)
A two-volume report for the UNU on the theme of the assessment of geomorphological problems in urban areas of drylands, by Ronald Cooke, D. Brunsden, J. C. Doornkamp and D. K. C. Jones, is designed to meet a number of objectives: to direct attention towards the environmental problems of urban areas in drylands; to analyse the extent of urbanization in drylands; to demonstrate how geomorphological information may be useful to planners and managers in the context of administrative systems in selectod urban areas of drylands; to display techniques used by geomorphologists in assessing drylands; and to evaluate each of the major environmental problems in drylands to which the geomorphologist has usefully contributed-aggregates, salinity, groundwater and salt-weathering problems, water and sediment problems, and problems of sand and dust movement.
The urban scene in drylands
Analysis of population statistics for drylands, a fairly difficult task, reveals several important phenomena. First, there are 355 cities with populations over 100,000 in the arid and semiarid lands (as defined by Meigs 119531), of which 208 are in Asia, 94 in the Americas and 53 in Africa. Secondly, dryland cities have been growing rapidly since 1950. For example, while word urban population has been growing at approximately 3.2 % p.a., that in dryland cities has been growing at an average rate of 3.9 %, with some rates as high as 16 % p.a. Unfortunately, few reliable data are available for centres smaller than 100,000, although it is clear that many of these have undergone phenomenal growth-the coastal settlements along the Arabian Gulf like Doha, Abu Dhabi and Sharjah provide spectacular examples.
Such population growth has led to extensive urban expansion. The amount of land consumed is in most cases rather difficult to determine. The environmental problems posed by this land vary greatly within the dryland zone, chiefly in terms of variations in climate and topography and, equally important, in terms of social, cultural and economic factors. In particular, some urban growth is planned-as in the USA and Israel-whereas in many less developed areas growth may be spontaneous and uncontrolled. Both types of growth may encounter geomorphological problems, but the planning and management of them is clearly only likely to be successfuI where appropriate agencies exist, and geomorphological information can be given to, and used by them.
Planning, management and geomorphology in dryland
Broadly, geomorphological studies of value to the management and planning in drylands fall into one of two main catogories.
First, there are those studies related to field mapping and resources evaluation before urban development actually begins. Geomorphology is particulary important here because landforms can provide a basis in drylands for regional classification of terrain as they are usually clearly displayed to the field observer or on remote sensing imagery, other environmental variables of interest are often related to them in a predictable way, they comprehensively cover the landscape (in drylands, other environmental phenomena, such as vegetation and soils often have only discontinuous distributionsl, and they are capable of hierarchical classification. Thus techniques of geomorphological mapping (as described in Chapter 111 of the report) can be seen as fundamental to resource appraisal not only because they provide an effective and relatively cheap means of generating valuable environmental data, but also because they can be adapted to surveys at different scales of enquiry, and the resulting maps can be used as a basis for other environmental surveys, and as a basis for the abstraction of data for specific problem orientated maps such as those of surface hazards.
Secondly, geomorphological studies dealing with the identification, monitoring and analysis of contemporary geomorphological processes-weathering, fluvial, slope stability and aeolian processes, for example-may contribute substantially to the day-to-day management of urban areas, and to ameliorating problems arising from conflict between the natural environment and urban development. Process studies require specialist techniques, many of which are used by, and some of which were developed by geomorphologists, and they often require substantial periods of time before sufficient data are available for reasonable predictions to be made of the magnitude, frequency, duration and impact of the processes. Such studies involve techniques of direct monitoring (as of aeolian processes, considered in Chapter VII of the report) and of indirect measures of process activity to analyse problems (as in the case of salt weathering, considered in Chapter V).
Geomorphological studies made before urban development are used chiefly to help identify the locations of resources or the range of locations suitable for particular activities, to assist the selection of suitable locations for particular activities within the range of possibilities, and to analyse conditions within selected locations in the hope that the use of resources will be more efficient and the avoidance of environmental hazards will be more effective. In addition, the geomorphologist hopes to prevent development from destroying or sterilizing valuable resources, to evaluate resources, and to limit the impact of environmental forces on the urban area and vice versa.
Geomorphological studies made during and after urban development are often used to minimize environmental impact and to provide a local temporal and spatial data base that facilitates the prediction of future changes and their continuous modification.
Use and value of geomorphological information in urban areas of drylands
Each urban area in drylands has its own unique suite of geomorphological considerations and its own distinctives ways of managing them within the local hierarchy of management organizations. A survey of the geomorphology-management links in Chapter 11 of the report reveals something of their variety.
Geomorphology and regional planning. At the scale of regional planning, geomorphological mapping and related research can often help in classifying terrain and locating resources.
Geomorphlogy in city planning. If geomorphological surveys are carried out sufficiently early in the planning of a new city, and their results are digested into planning discussions, some of the potential dissonance between environmental conditions and the city plan can be avoided.
Geomorphology in site development. Geomorphological contribution to site development include aid in rationalising site plans to avoid hazards, formulation of building and site choice adapted, and sampling sites for ground material investigations.
Geomorphology and post-construction management. The monitoring of geomorphological processes and landform changes after construction can play an important role in helping enviroomental managers to influence future planning policy and alleviate or avoid environmental hazards.
The way forward
The philosophy and methods described in the UNU report have been well-tested in many arid environments. Geomorphological advice is commonly sought on a consultancy basis by planners, engineers, politicians and private citizens in the more affluent of dryland countries such as those in North America, Australia and the Middle East.
A first priority for further research on the foundations laid in the UNU report should be to bring geomorphological advice and experience to bear on urban development in those dryland cities where planning is absent or rudimentary, local experience is scarce, and financial resources for such investigations are limited. The experience of the Bahrain Surface Materials Resources Survey (Doornkamp, Brunsden and Jones, 1979) makes it clear that it is neither too ambitious nor too arrogant to undertake such studies. Amongst the larger urban dryland regions that suffer from immense problems of uncontrolled growth and which might welcome such assistance are Lima, Dakar, Baphdad, Karachi, Ankara, Santiago (Chile), Caracas and Maracaibo.
An alternative strategy to the commissioning of comprehensive, city-region surveys would be to promote field studies of specific problems common to many arid urban areas in order to improve understanding of the problems and accelerate the innovation of satisfactory management practices. For example, salt-weathering hazards have now been studied in detail in only three areas-Bahrain, Dubai and Suez-the potential for further studies along the saline, urban coasts of deserts is great. Flooding and aeolian problems are additional, understudied, but serious problems requiring international attention.
A third possibility relates to the specific needs of dryland engineers. While the studies in the report on geomorphological mapping, salt problems, aggregates, and wind and water problems provide a contemporary summary, they could each be extended and modified through further review to provide detailed manuals for environmental managers, providing extensive consideration of field and laboratory techniques.
A further research possibility wouid be to examine in detail the fate of selected applied geomorphological studies in drylands-the extent to which they have actually been used-in order to discern more clearly which kind of information has been most effective and the relative success of different ways of injecting it into the management system.
References
Cooke, Ronald; Brunsden, D.; DoornkampJ.C.; Jones, D.K.C. 1979. Assessment of geomorphological problems in urban are of drylands. Tokyo,
United Nations University. To be published by Oxford
University Press. 2 vol. Doornkamp, J. C.; Brunsden, D.; Jones,
D. K. C. (eds). 1979. Geology,
geomorphotogy and pedology of Bahrain Norwich, Geo Books.
Horst Mensching, professeur
L'lnstitut de géographie de l'Université de Hambourg (République fédérale d'Allemagne) a un programme de recherche.s dirigé par le professeur Horst Mensching sur les problèmes d'aridité en Afrique sahélienne. Outre de nombreux travaux sur l'Afrique orientale au Soudan on peut signaler l'ouvrage de Thomas Krings sur Le changement en géographie culturelle dans la région de contact des nomades et des paysans au Sahel voltaïque: l'exemple de l'Oudalan dont voici le résumé.
Dans la zone de contact des nomades et paysans du Sahel voltaïque (au nord du 14 parallèle) on a pu constater, depuis quelques décennies, de profonds changements dans la structure géographique humaine. D'une part, ce sont des changements dans les sociétés traditionnelles des différents peuples sahéliens et, d'autre part, des changements dans leurs genres de vie et leurs systèmes agropastoraux. Ces évolutions étaient responsables d'une détérioration de l'ecosystème sahélien. Plusieurs facteurs sont 3 mentionner pour expliquer ces changements:
L'émancipation sociale de la caste d'esclave chez les Touareg (Iklan). La pression démographique dans les sociétés paysannes. L'augmentation du cheptel bovin pendant les années avant la sécheresse.Le processus continuel de la sédentarisation chez les nomades.
Ces facteurs étaient responsables de l'énorme extension des
champs de mil pendant les derniers vingt-cinq ans dans le Sud
Oudalan, dans la zone de contact des nomades et paysans. Sur la
base d'une interprétation comparative des photos aériennes des
années 1955 et 1974 l'extension des superficies agraires de plus
de 60 % est observée. De la sécheresse résultait un changement
dans la structure de l'élevage. Entre 1968 et 1973, le cheptel
bovin de l'Oudalan se réduisit de plus de 70 %. Chez les Touareg
et les Iklan l'élevage des chèvres est devenu de plus en plus
important. En revanche, chez les pasteurs peul, les pertes de
bétail ne furent pas aussi graves. Les Peul purent maintenir
leurs systèmes agropastoraux dans la plupart des cas, 3 cause de
leur genre de vie bien adapté aux conditions écologiques du
Sahel. Comme résultat de ces changements géographiques humains,
on peut constater pour le Sud Oudalan-où les cultivateurs et
nomades vivent en symbiose- les plus graves effets pour
l'écosystème (désertification) 3 cause de surpâturage et de
l'extension de la culture du petit mil en combinaison avec
l'élevage des chèvres désestreux pour le tapis végétal.
Aussi, sur les anciens systèmes dunaires, de vastes superficies
sont affectées par la désertification (voir les photos
aériennes). Dans le nord, le domaine traditionnel des nomades,
domine l'utilisation pastorale extensive. C'est pourquoi on
observe, en milieu nomade, seulement des dégâts ponctuels aux
alentours des mares et puits (par exemple aux environs de la Mare
d'Oursi).
Annexes