TRANSECT SAMPLING STRATEGIES FOR SEMI-DETAILED CHARACTERIZATION OF INLAND VALLEY SYSTEMS

For the semi-detailed characterization of inland valleys systems, the Inland Valley Consortium (IVC) uses transect sampling to describe vall ey morphology, soils, and land use characteristics. Initially, for eac h valley one transect with a width of 200 to 400 m was proposed. More recently, use of a larger number of transects has been suggested. Howe ver, there is no statistical basis for either the number of transects to be described or their optimal width. Two sets of aerial photographs (1979, scale 1:50,000, and 1996, scale 1:20,000) of the Boundiali key area were processed and the results digitized. Using GIS, sets of tra nsects with different width were made, and used for the determination of the sample size for estimating the land use ratio and the valley bo ttom ratio at valley system level with given confidence intervals. The se results were validated with data from the field and with sets of pr e-selected transects. The calculated sample size is based on simple ra ndom sampling and depends on both transect width and variability in th e study area. For the characterization of inland valleys with reasonab le confidence intervals, the sample size for random sampling is too la rge for the IVC semi-detailed characterization method.Smaller samples of transects selected on the basis of sub-recent aerial photographs ga ve comparable results for land cover characteristics estimation as the larger samples for random sampling. It is, therefore, concluded that there is scope for reducing sample size by formalizing criteria for tr ansect placement on the basis of sub-recent aerial photographs.