Conventional hydrogeological, hydrochemical and environmental isotope study of the Sandspruit River Catchment, Berg River Basin, South Africa.
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Date
2012
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Abstract
The Sandspruit River catchment, found within the heart of the Swartland region is infamous
for wheat and wine production. Variable groundwater quality and low productivity is
encountered within the folded and fractured Malmesbury Group aquifer, whilst the most
productive and better quality groundwater is found within the Table Mountain Group
sandstone. The Sandspruit catchment (a tributary of the Berg River) represents a drainage
system, whereby saline groundwater with TDS up to 10870 mg/l, and EC up to 2140 mS/m
has been documented. The catchment belongs to the winter rainfall region with precipitation
seldom exceeding 400mm/yr, as such, groundwater recharge occurs predominantly from
May to August. Recharge estimation using the catchment water-balance method, chloride
mass balance method, and qualified guesses produced recharge rates between 8-70 mm/yr.
To understand the origin, occurrence and dynamics of the saline groundwater, a coupled
analysis of major ion hydrochemistry and environmental isotopes (δ¹⁸O, δ²H and ³H) data
supported by conventional hydrogeological information has been undertaken. Research data
were collected in three seasonal field sampling campaigns within the study catchment.
These spatial and multi-temporal hydrochemical and environmental isotope data provided
insight into the origin, mechanisms and spatial evolution of the groundwater salinity. These
data also illustrate that the saline groundwater within the catchment can be attributed to the
combined effects of evaporation, salt dissolution, and groundwater mixing. The geology
together with the local and regional faults control the chemistry of the groundwater, whereby
relatively fresh groundwater can be observed in certain direct recharge areas. The salinity of
the groundwater tends to vary seasonally and evolves in the direction of groundwater flow.
The stable isotope signatures further indicate two possible mechanisms of recharge; namely,
(1) a slow diffuse type modern recharge through a relatively low permeability material as
explained by heavy isotope signal and (2) a relatively quick recharge prior to evaporation
from a distant high altitude source as explained by the relatively depleted isotopic signal and
sub-modern to old tritium values. A conceptual hydrogeological model based on the
hydrogeological, hydrochemical, and environmental isotope data was developed for the
Sandspruit catchment. This model, together with statistical and groundwater quality analysis
has lead to the development of a proposed local optimized monitoring scheme for the
catchment.
Description
Thesis (M.Sc.)-University of KwaZulu-Natal, Westville, 2012.
Keywords
Sandspruit River Watershed (Western Cape), Berg River Watershed (Western Cape), Groundwater--Western Cape--Berg River Watershed., Water quality--Western Cape--Berg River Watershed., Hydrogeological modeling--Western Cape--Berg River Watershed., Water chemistry., Theses--Geology.