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Durham University (1988)

Analysis of relief, slopes and summits in the Thaniyat Turayf, N.W. Saudi Arabia

Al Mazrooa, H.S

Titre : Analysis of relief, slopes and summits in the Thaniyat Turayf, N.W. Saudi Arabia

Auteur : Al Mazrooa, H.S

Université de soutenance : Durham University

Grade : Master of Science (MS) 1988

Three different methods have been successfully demonstrated in this study of the geomorphology of arid desert terrain in north western Saudi Arabia. Each of these methods is based on the collection of data pertaining to some landform characteristic and then transformed into more meaningful terrain characteristics to provide quantitative representation of the geomorphologic character of the area. The summit mapping approach, described in Chapter 3 is considered the least satisfactory approach for analyzing the geomorphology. It is essentially a manual data collection procedure and extremely tedious. This method is suitable only for the analysis of an area covering an entire mountain block, the limits of which cannot always be defined using any standard criterion. As pointed out earlier, the only stable and meaningful landform parameter resulting from this analysis is the closure intensity, which represents the average ridge line gradient and may be used to compare the geomorphology of two mountain blocks. The approaches used for the altitude analysis of Wadi Umm Al Arta in Chapter 5 and for relief analysis of Thaniyat Turayf area presented in Chapter 4 are both dependent on altitude data interpolated from a topographic map at some regular grid interval. Although a manual procedure was used to extract the altitude data in this study, techniques are now well-developed to generate digital elevation models of any terrain surface of interest photogrammetrically through aerial photography. Thus the entire process of altitude data collection as well as processing can easily be automated. Altitude above sea level, by itself, does not provide full information about the landform as Evans (1972) has so convincingly pointed out ; its derivatives such as gradient aspect, profile convexity and plan convexity toether provide a complete and meaningful quantitative portrayal of the local land form. However, the spacing at which the altitude data is captured should be dictated by the topography. It should rarely be necessary to use grid spacing smaller than 100 metres. In fact the digital photogrammetric technology available today can provide very dense terrain elevation data. Once captured, the data can be processed using any grid spacing commensurate with the topography of the terrain. There is no doubt that the relief is a far more informative statistic than the altitude above the sea level. But the magnitude of relief is dependent on the horizontal interval over which relief is measured. For the same Thaniyat Turayf study area, the average relief is 38.7 m for 1 x 1 km spacing and changes to 59.5 m when the grid spacing is enlarged to 2 x 2 km (Table 4.6). So if two areas are to be compared, then relief must be measured at the same grid spacing. The derivatives of relief such as relief gradient and relief profile convexity are relatively independent of the grid spacing used and are more stable terrain parameters for comparison. The physical significance of the plan convexity for relief is not very clear. In conclusion, it may be stated that although each of the methods demonstrated in this study can be used for the morphometric analysis of landform, the measurement of evenly spaced altitude data and the computation of altitude derivatives - gradient, aspect, profile convexity and plan convexity - provide the most complete and meaningful information about the landform. The fact that this approach can easily be adapted to the use of digital computer for data capture, data analysis as well as for graphical display of the computed results should add further impetus to wider application of this approach


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