- Title
- An assessment of the hydrologic response of the Keiskamma catchment to land use/cover changes
- Creator
- Sive, Mlamla
- Subject
- Hydrological response
- Date Issued
- 2019
- Date
- 2019
- Type
- Thesis
- Type
- Masters
- Type
- MSc
- Identifier
- http://hdl.handle.net/10948/44732
- Identifier
- vital:38165
- Description
- The Keiskamma catchment has undergone significant land use/cover changes (LUCC) underpinned by land use policy reforms and climate change. However, the hydrological responses of the catchment to LUCC are not fully understood. This study sought to assess the hydrological response of the Keiskamma catchment to LUCC at catchment and hillslope scale using remote sensing, GIS, hydrological modelling and field experiments. Catchment scale assessments first involved LUCC mapping in IDRISI TerrSet software, using supervised image classification for two sets of multispectral imagery; namely Landsat Thematic Mapper (TM) of 1994 and Landsat 08 Operational Land Imager (OLI) of 2016. The LUCC maps provided an indication of LUCC over time and were prerequisite land use inputs for modelling the hydrologic response of the catchment. The Soil and Water Assessment Tool (SWAT) hydrologic model was used to model the hydrologic response of the catchment to LUCC. The Sequential Uncertainty Fitting (SUFI-2) in SWAT-CUP was used to assess model performance and uncertainty analysis. The influence of rainfall on the hydrologic response of the catchment was also assessed using linear regression. One of the prominent forms of LUCC in the Keiskamma catchment, particularly central Keiskamma is P. incana shrub encroachment. Field experiments were set up to investigate the hydrologic impacts of P. incana shrub invasion at hillslope scale, as well as to validate the results obtained by the SWAT hydrologic model. Field experiments included an assessment of the Landscape Organisation Index (LOI) of the invasion, as well as assessing of surface conditions, surface runoff (L), volumetric soil water content (cm³/cm³) and sediment loss (grams) under P. incana, grass and bare-eroded areas. High image classification accuracy assessment values of 87.2 % and 87.4 % for 1994 and 2016 respectively were obtained, with a Kappa coefficient of 0.84 for both sets of imagery. Results of the study revealed a significant increase in woody vegetation encroachment, specifically shrub invasion, forest expansion in the upper parts of the catchment, as well as an increase in exotic and invasive vegetation species within the riparian zone. The SWAT model showed a good (NSE=0.69, R²=0.69 and RSR =0.56) and unsatisfactory (NSE=0.4, R²=0.4 and RSR 0.79) model performance for calibration and validation respectively. However, for both the calibration (p-factor =0.77; r-factor 1.03) and validation (p-factor =0.92; r-factor 1.38) periods there was acceptable uncertainty as indicated by the p- and r-factor statistics. The mean annual streamflow (-71.4 %), surface runoff (-98.8 %), soil water content (-4.5 %), evapotranspiration (-5.3 %), groundwater (-79.5 %) and sediment loss (-99.9 %) decreased from 1994 to 2016. The impoundments in the catchment viz Cata, Mnyameni, Binfield, Sandile, Debe and Dimbaza dams, also contributed significantly to the streamflow reduction. A strong correlation (r= 0.61) between the declining streamflow (m3/s) and rainfall (mm) was observed. At hillslope scale, P. incana invasion was characterised by a low LOI, owing to large inter-shrub bare patches and poor soil surface conditions characterised by soil surface crusting, conducive to high runoff generation and connectivity. High surface runoff and soil losses were evident under P. incana and bare-eroded areas. Volumetric soil water content was high under grass and P. incana tussocks, intermediate in P. incana inter-patches and low in bare-eroded areas. The findings and analysis of this study conclude that the hydrologic response of the Keiskamma catchment was influenced significantly by LUCC in the form of extensive invader shrub encroachment, expansion of forestry using exotic tree species, impoundments, as well as the infestation of riparian zones by invasive vegetation. Management of woody shrub encroachment and alien invasive plants as well as indigenous forest species utilisation should be considered as amongst the key efforts towards restoring the ecohydrological integrity of the Keiskamma catchment.
- Format
- x, 146 leaves
- Format
- Publisher
- Nelson Mandela University
- Publisher
- Faculty of Science
- Language
- English
- Rights
- Nelson Mandela University
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NMU School of Environmental Sciences
| Thumbnail | File | Description | Size | Format | |||
|---|---|---|---|---|---|---|---|
| View Details Download | SOURCE1 | Mlamla, S 213219573 Dissertation Dec 2019.pdf | 3 MB | Adobe Acrobat PDF | View Details Download |