This study was aimed at studying bulkflow parameters in groundwater systems at
littoral zone of the Modder River. In this thesis, all the aspects were synthesised and
exemplified by incorporating a multidisciplinary perspective to develop a sound
conceptual framework of the alluvial stream aquifer system.
Hydraulic characterisation of the near aquifer system was achieved by acquiring data
from a 6-spot pattern well network from which lithological, aquifer hydrogeology, and
groundwater hydrogeochemistry characterisations were comprehensively
undertaken.
The aquifer overburden was estimated to have the permeability of 2.42m/d when its
textural classification was found on average to consist of 22% clay+silt and 77% very
fine sand. The geology of the study area is typical of the Karoo geology. This was
affirmed by massive mudstone bedrock of the Ecca group underlying the study
domain. The unconsolidated sediments of gravel, sand and silt, overlie this Karoo
mudstone. Therefore, the aquifer is a three units and unconfined alluvial stream
aquifer situated in the alluvial deposits along the course of the Modder River. The
main units of the system are the upper unit, middle unit and lower aquitard made up
of the overbank-fine sand deposits, gravel and mudstone respectively.
Groundwater is a bicarbonate type water and falls along a mixing line from sulfatechloride
type water to calcium-magnesium type water. This water was found to be
both unpolluted sodium enriched and chloride enriched strongly be attributed to
forestation of the site where evapotranspiration rates are widespread. Groundwater
plots close and parallel to GMWL indicating that recharge is primarily derived from
the direct infiltration of precipitation.
The δ18O and δD composition of water from the sampled wells indicates that water
from all wells drilled in the Riparian or Bank storage aquifer is isotopically lighter than
water from wells located on the Terrestrial aquifer. Tritium ranges are indicative of
modern water suggesting that the possible influx source might have been
precipitation or precipitation derived water. In other words, the groundwater gets
recharged with modern rainfalls and has short circulation time in the ground
indicative of short travel time. The plot of pH-Tritium indicates that the majority of the samples fall within the rage 6 to 8.5 attributed to recharges with modern and highly
neutralised rainfalls. This also suggests short groundwater circulation time in the
ground. The groundwater samples with the lowest nitrate concentration were the
ones with the lowest tritium level indicating that, although the groundwater source
lies on agricultural land, it has not been contaminated by nitrate fertilizers.
Groundwater head differences yield the hydraulic gradients from terrestrial aquifer
towards riparian aquifer. On average the hydraulic gradient is 0.0083. Flow direction
over the entire study domain generally trend SE, sub-perpendicular to the regional
surface water flow direction. The EC-profiles show the gravel unit as a major
groundwater conduit as shown by a jump in EC values at this unit and this unit is the
same water source for all the wells that intercepted the gravel.
The transmissivity of the siteâs aquifer ranges between 0.3m2/d and 164m2/d.
Highest transmissivity estimated at a maximum level are observed in wells located in
the riparian aquifer. The unconfined aquifer specific yield is in the order of 0.005-
0.023. Darcy velocity was estimated at 4.16m/d for CYS1BH4 and natural flow
velocity for this well was ultimately estimated at 1.81 m/d. On the other hand, Darcy
velocity for CYS1BH3 was estimated at 9.01 m/d with natural flow velocity ultimately
estimated at 3.92 m/d. Last in the list is CYS1BH5 whose Darcy velocity was
estimated at 11.24 m/d and natural flow velocity ultimately estimated at 22.4 m/d.
The estimated velocities are relatively high and this observation holds true for
transmissivities so high.
Baseflow calculations gave a negative value signifying no base flow contribution of
groundwater in to the river. This suggests that most groundwater is used up by the
riparian vegetation.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ufs/oai:etd.uovs.ac.za:etd-08162012-105500 |
| Date | 16 August 2012 |
| Creators | Shakhane, Teboho |
| Contributors | Prof G Steyl |
| 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-08162012-105500/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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