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Trente ans de lutte contre l’onchocercose en Afrique de l’Ouest. Traitements larvicides et protection de l’environnement

Laurent Yaméogo
Christian Levêque
Jean-Marc Hougard

Environmental Impact Assessment of Settlement and Development in the Upper Léraba Basin

Annex 1. Summary of Cartographic Activities and Vegetation Profile Construction

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Medium-scale Mapping: Land Utilization Patterns in the Upper Léraba Pilot Study Area in Burkina Faso and Côte d’Ivoire

1The first map prepared, concerning and the lower stretches of L.oc and L.or, was at scale 1: 50 000, and in black/white. It covered an area of ca 400 km2 upstream of Léraba Bridge, and embraced total valley and channel lengths of 36.3 km and 75.5 km, respectively. It displayed the cultivated/deforested areas discernible in 1993, together with information on the land utilization situations in 1972 and 1983.

2Partly because it was impracticable to include such a large map in this paper, and partly because there was an unavoidable loss of definition in photocopy reductions of the original map, all land utilization data were computerized according to year, so that they were in a more manageable format for analysis and for inclusion in this paper (maps in Figures 4.1 to 4.6). Although those maps are presented in black/white, the originals were constructed in color, so that large format prints could be used for demonstration and training purposes.

Local-scale Mapping: Vegetation of the Léraba Valley Upstream of the Road Bridge

3This map was originally constructed at scale 1:2 500, to facilitate longitudinal studies on vegetational changes, especially with regard to riverine forest. The map covered 1.86 km of valley within an area of approximately 1.5 km2. River channel lengths were, 1.73 km above Léraba Bridge, and 0.26 km below it. The map boundary was purposely extended towards the southeast, to allow the whole of Lérabadougou village to be included.

4The main feature of the map, the zonation of vegetation communities (generally parallel to the center line of the watercourse), which was a typical feature of rivers in the Sudanian savanna vegetation zone (Molyneux et al, 1978), were clearly depicted. The map also showed some areas of cultivation; generally located in woodland above the 280m contour line, and not usually extending into the floodplain grasslands.

5This map was also reduced and re-drawn to enable it to be included in this paper, as Figure 4.6.

Vegetation Profiles

6On the basis of the aerial photographs that were used to prepare the maps described above, some schematic vegetation profiles were developed across and at right angles to the course of the main Léraba river. These are depicted in Figures 2.2 and 4.5, and discussed in the main body of the paper.

7In each of the illustrated profiles, the lower, shaded part represents the substrate. Its upper margin represents the surface of the ground, which supports various types of vegetation (trees, shrubs, grasses, etc) and which form different types of botanical communities. For the sake of clarity, the vertical scale has been exaggerated.

8The transects used for the construction of the profiles presented in Figure 4.5 are marked as straight lines (A-A, B-B and C-C) on the map shown in Figure 4.6.

© IRD Éditions, 2003

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