Natural vegetation has been converted to land uses, such as agriculture, commercial forestry
and urban use, to meet increasing human demands for food, fuel and shelter. These land use
changes modify the surface conditions of an area, resulting in changes in hydrological
responses. Urban land use, in particular, has a significant impact on catchment hydrology as a
result of the increased impervious areas such as concrete, tar and roofs. To assess the future
hydrological impacts of urban land use, the scale and location of future urban areas must be
considered. The objective of this study was to assess the hydrological responses to future
urban growth in the Mgeni catchment, South Africa. An urban growth model was used to
generate scenarios of plausible future urban growth and these scenarios were modelled using
a hydrological model to determine the hydrological responses to urban growth.
The plausible future urban growth in the Mgeni catchment was modelled using the SLEUTH
Urban Growth model (SLEUTH). The SLEUTH acronym stands for the input layers required
for the model viz. Slope, Land use, Excluded areas, Urban Extent, Transport routes and
Hillshade. SLEUTH is able to provide the scale and location of future urban growth required
to assess the hydrological impacts of future urban growth. The data requirements and
modelling procedure for SLEUTH is relatively simply and therefore it is well suited to a
South African context. SLEUTH was calibrated and applied to the Mgeni catchment to
project future urban land use. When assessing the 95-100% probability class, the results
revealed that the Henley, Pietermaritzburg and Durban areas would experience the highest
urban growth in the Mgeni catchment by the year 2050. The outputs of the SLEUTH Model
for the Mgeni catchment showed a number of similarities to another application of SLEUTH
in Cape Town. These similarities indicate the SLEUTH performs in a similar way for the two
South African cities. Therefore, it was concluded that the SLEUTH Model is suitable to
account for urban growth in the Mgeni catchment, as required for use in hydrological impact
studies.
The hydrological responses to urban growth in the Mgeni catchment were assessed using the
ACRU model. The scenarios of plausible future urban growth generated by SLEUTH were
overlaid with current land cover layers to generate maps of plausible future urban land use.
The results showed extensive urban growth of >95% probability occurring in the Midmar,
Albert Falls, Henley, Pietermaritzburg, Table Mountain, Inanda and Durban Water
Management Areas (WMAs) by 2050. Increases in mean annual streamflows were observed
in many of these areas; however the Henley, Pietermaritzburg and Table Mountain WMAs
were shown to have greater increases in mean annual streamflow than the other areas that
showed similar increases in urban growth, thus indicating that these WMAs could be
particularly responsive to urban growth in the future. Furthermore, the results showed that the
type of urban land use is important in determining the hydrological responses of urban land
use, as the imperviousness differs between the different urban land uses.
Streamflow responses were shown to be influenced by the scale and location of urban growth
in the Mgeni catchment and specific areas, such as the WMAs along the Msunduzi River,
were identified as potentially responsive to urban growth. Summer streamflows were
indicated as being more responsive to urban land use changes than winter streamflows and
increases in streamflows due to urban growth start to over-ride the impacts of other land uses
which have substantial impacts on hydrological responses such as commercial forestry, and
commercial sugarcane by 2050, whereas in other areas increases were mitigated by the
presence of major dams. Lastly, it was shown that the type of urban land use, such as built up
urban areas when compared to informal urban areas for example, have a significant impact on
streamflow responses. These results are useful as they can be used to inform both water
resources planning as well as urban planning to ensure that South Africa’s valuable water
resources are protected. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2012.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ukzn/oai:http://researchspace.ukzn.ac.za:10413/9488 |
| Date | January 2012 |
| Creators | Mauck, Benjamin Alan. |
| Contributors | Warburton, Michelle Lynn., Jewitt, Graham Paul Wyndham. |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
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