There is an interactive relationship between soil and hydrology. Water plays a primary role in the
genesis of most soil properties and soil properties influences and governs hydrological
processes. Incorporation of these processes into hydrological models is essential for water
resource management. Hydrological processes are dynamic in nature with strong temporal
variation, making measurements expensive, inaccurate and time consuming. Predictions of
these processes, especially predictions in ungauged basins (PUB) are therefore essential. Since
soil properties are both a cause and result of this interactive relationship, identifying and
interpreting relevant soil properties, can reveal information on key hydrological processes.
The hypothesis is then that soil properties can serve as signatures of hydrological
characteristics. Identifying these and interpreting them and their relative distribution at hillslope
scale can lead to better understanding of hillslope hydrological response and facilitate the
formulation of conceptual hillslope hydrological models. These models can aid in the prediction
of hydrological processes in ungauged basins (PUB).
Hydrologically there are three main soil types namely recharge, interflow and responsive soils.
Data from previous studies were utilized to accentuate the differences between these soil types.
A criterion for distinguishing between two storage mechanisms (perennial and transient
groundwater) in the soils of South Africa is also proposed.
Two catchments in the Eastern Cape of South Africa were selected for this study:
A hillslope in the upper catchment (Uc) of the Weatherley was selected to determine the impact
of soil types on hydrological response. A conceptual model was developed based on soil
morphological properties and their relative distribution. These morphological properties included
soil depths, mottling, and clay contents. These properties indicate that there are definite
recharge, interflow and responsive areas in this hillslope.
The conceptual model was then evaluated with the use of climate, tensiometer, neutron water
meter, hydrograph and evapotranspiration (ET) data. The conceptual model and soil information were utilised to calculate the relative contribution of streamflow generation mechanisms. Base
and peakflow calculations gave a very good estimation of the actual streamflow.
In the greater Bedford catchment, three sub-catchments (B3, B4 and B5) were surveyed for
hydropedological purposes. All the soil properties which might influence or be influenced by the
hydrology were identified and related to hydrological hillslope response. These properties
include: soil type, soil depth, weathering of underlying material, and presence of CaCO3.
Conceptual models of representative hillslopes in the selected catchments were developed
based on the interpreted soil information. The dominant factors governing the streamflow in
catchment B4&5 was shallow soils on bedrock with restricted permeability, which facilitated
overland flow. In B3 the deeper soils and permeable bedrock facilitated infiltration, interflow as
well as recharge of water tables (regional and perennial).
Two levels of detail of soil information namely; Land Type data: level 1 and Observed data: level
2, were used to test the impact of soil information on hydrological modelling. The results were
assessed to evaluate the contribution of soil data and the effectiveness of the conceptual model.
The contribution of some streamflow generation mechanisms was also calculated.
A method for classifying soils based to their hydrological behaviour was proposed. Future
research should focus on several aspects (soil water regime, ET, drainage curves, hydraulic
conductivity, flowpaths and storage mechanisms) which describe the hydrology of soil of South
Africa. Such a system can benefit hydrological modelling, especially in PUBâs.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ufs/oai:etd.uovs.ac.za:etd-10092009-161842 |
| Date | 09 October 2009 |
| Creators | van Tol, Jacobus Johannes |
| Contributors | Dr PAL le Roux |
| Publisher | University of the Free State |
| Source Sets | South African National ETD Portal |
| Language | en-uk |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.uovs.ac.za//theses/available/etd-10092009-161842/restricted/ |
| Rights | unrestricted, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to University Free State or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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