Browsing by Author "Malan, Gert Jacobus"
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- ItemInvestigating the suitability of land type information for hydrological modelling in the mountain regions of Hessequa, South Africa(Stellenbosch : Stellenbosch University, 2016-12) Malan, Gert Jacobus; De Clercq, W. P.; Rozanov, Andrei Borisovich; Stellenbosch University. Faculty of AgriScience. Dept. of Soil Science.ENGLISH ABSTRACT: The Land Type database of South Africa combines soil associations with various terrain positions within a larger Land Type polygon. The Land Type structure provides the opportunity to unlock the terrain unit information through segmenting the larger Land Type polygon into terrain units. Geographical information systems have the capability to dissect the landscape into terrain morphological units, using remote sensing technology. There is a range of methods and software available that can be used to dissect the landscape, the challenge is to identify a method that would be compatible with Land Type terrain units. The study area is the catchment of the Korentepoort dam, north of Riversdale in the Hessequa district of the Western Cape. The Hessequa region is regularly struck with drought which leads to an investigation into the water security of the region. The investigation includes the development of a hydrological model for the Korentepoort Dam and bordering catchments. Physically based hydrological models require detailed soil distribution maps with soil physical data. The physical characteristics are used to calculate the amount of surface runoff, drainage and streamflow. Hydrologists use the Land Type information to supply soil character for modelling purposes. The most common soil type from the Land Type memoir is selected to represent the whole Land Type polygon. This representation varies depending on the homogeneity of soils within the landscape, but can be as little as 20%. The segmentation method is evaluated within the Korentepoort catchment by field observations of the terrain at 190 points in the landscape. This point data is compared to the segmentation map with a different range of acceptable error. The segmentation method is constructed on a 90-meter digital elevation model, which was refined to a 30 meter. The highest acceptable error was selected as 30 meters. At this error, the terrain map was able to predict 77% of the field observation points. Transects were created from the terrain map, which also indicates a good fit with terrain units. The Land Type information in the catchment was found to be conflicting with field observations and thus updated. The updated Land Type information was used to populate the segmented terrain map. The high resolution of the terrain map was found to be too complex for the hydrological model. A well-used method of soil type aggregation on the basis of hydrology was applied to the updated Land Types. The method divides the soil types into three hydrological response units and was found to be accurate on 10 out of 13 selected profiles. These profiles are selected as modal profiles and represent the soil types of their respective terrain units. This research made it possible to dissect the landscape into units comparable with those in the Land Type database. This increases the resolution of the Land Type information and could possibly be applied to the whole of South Africa. Methods are suggested in which these terrain maps can be aggregated in a meaningful manner which would enhance its applicability for hydrological modelling.