Document Type

Dissertation - Open Access

Award Date

2018

Degree Name

Doctor of Philosophy (PhD)

Department

Civil and Environmental Engineering

First Advisor

Suzette Buckhard

Second Advisor

Laurent Ahiablame

Keywords

Arid and Semi arid regions, groundwater resources, hydrologic modeling, low Impact developments, surface water resources, water resources engineering

Abstract

Climate variability need to be incorporated into the management and planning of water resources, particularly in arid and semi-arid regions, where water availability is more sensitive to rainfall and air temperature. This study used modified Man-Kendall trend analysis test and ArcGIS to process data. Annual means of rainfall, minimum temperature and maximum temperature in the Limpopo River Basin (LRB) varied between 160 and 1109 mm, 8 °C to 20 °C and 23 °C to 32 °C respectively. The spatial pattern is generally increasing from west to east for rainfall and minimum temperature while maximum temperature increases from south to north and west to east. Coefficient of variation (CV) shows an opposite pattern to the annual pattern, with rainfall showing the highest variation compared to other variables. Rainfall and minimum temperature showed an increasing pattern in most of the basin while maximum temperature showed a decreasing pattern. In-depth understanding of the hydrological processes is important for balancing availability and demand for water. As part of this basin-wide and the basin nations concern, this study examined blue and green freshwater availability and identified water sensitive areas by balancing water availability and demand for the Limpopo River Basin (LRB). The Soil and Water Assessment Tool (SWAT) model, calibrated at multiple locations in the basin for monthly streamflow simulation showed satisfactory results, given the scale and variability in physical characteristics of the basin. Spatial analysis showed a decreasing pattern in freshwater availability from east to west, and from north to south while temporal variation showed alternate episodes between wet and dry years, with deviations from the normal cycle every one to two years for the wet periods and three to five years for dry periods during the study period. 20% in the east of the basin show excess wetness while the rest of the basin is dry areas. Understanding the rate, timing, and location of groundwater recharge, groundwater levels and discharge characteristics are crucial for efficient development and management of groundwater resources, as well as for minimizing pollution risks to the aquifer and connected surface water resources. SWAT-MODFLOW was used to characterise the distribution of annual and seasonal groundwater recharge, groundwater level, groundwater–surface water interactions in the LRB from 1984 to 2013. The impacts of Low Impact Developments (LID’s) and Best Management Practices (BMP’s) on groundwater recharge and water table elevations were also assessed for the Gaborone catchment as a case study in the LRB. Simulation results show relatively high annual recharge along the Limpopo main river and at the outlet of the basin. The groundwater table is generally shallow in the rainy east and along the basin’s river network. Seasonal analysis reveals high variability in both groundwater recharge and level. The summer season has the highest groundwater recharge, followed by autumn, spring, and winter as the lowest recharge during the 30-year study period (1984 to 2013). Water table elevations are low in the summer and highest in the autumn. In terms of groundwater-surface water interactions, rivers in the south showed input from groundwater discharge while west river channels appeared to seep to the underlying aquifers. Implementation of the LID practices resulted in 0 to 6% increase in annual groundwater recharge and 0 to 0.11% increase in annual water table elevations.

Format

application/pdf

Number of Pages

153

Publisher

South Dakota State University

Rights

In Copyright - Non-Commercial Use Permitted
http://rightsstatements.org/vocab/InC-NC/1.0/

Available for download on Tuesday, May 05, 2020

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