The hydrogeology of the Tono basin, Japan, is strongly inuenced by the hydraulic
properties of faults, especially the main Tsukiyoshi fault, which extends
through the centre of the assessment area and has an E-W strike. According to the
results of borehole investigations, the fault has N800W strike, 700 dip, 10 ô 30m
width and approximately 30m vertical off-set. Hydraulic head discontinuities over
the main fault in the basin are about 40 m as a result of the low permeability of the
fault acting as a barrier to ow perpendicular to it. The fracture data from the Tono
basin was analysed in order to establish a correlation between geologic/geometric
attributes of a fracture and associated permeability of the interval that contains the
fracture, if any. Pressure response transients to excavation of two shafts that are
monitored at various boreholes within the study site show that proximity to a fault
is a key attribute that determines the ability of the fracture to conduct water. The
responses in boreholes that are close to the fault are vertically invariant, indicating
a large vertical permeability. This is not the case in boreholes that are further
from the main fault, where there is depth dependence in the pressure responses.
Near the fault, the damage zone seems to be equilibrating the heads between otherwise
unconnected aquifers. The Tsukiyoshi fault therefore acts as barrier to ow
perpendicular to it but also acts as conduit to vertical ow and ow parallel to the
fault. A three-dimensional model that simulates groundwater ow in the Tono basin
is constructed in order to study the dynamic uid ow before and after it was disturbed
by production and the excavation of the shafts. In the steady-state calculation,
the model predicts that the hydraulic head at depth in boreholes near the fault
is near the land surface. This condition indicates high vertical permeability in those
boreholes.
This thesis introduces a new approach of using pressure response data to do
an inversion calculation for the effective porosity of the granite. Pressure response
transients have been analysed using a numerical inversion procedure to estimate
the specic storage of the granite. The specic storage was calculated using the
pressure response data and ranged from 4:12 10ô7 to 8:93 10ô6mô1.
These values of the specic storage were used to do a transport calculation
in order to study the impact of the main fault on the transportation of hypothetical
contaminants in the basin. Particle tracking was used to investigate and demonstrate
the effects of the fault on path lines. The fault was found to have a strong inuence
on the transportation of contaminants. The general trend of the transportation of
the contaminants follows groundwater ow from the northern high elevations toward
the southern low elevation. This shows that the contaminants are transported
mainly by advection. However, this trend is interrupted by the Tsukiyoshi fault
that blocks horizontal ow and sends water toward the surface. An interesting feature
demonstrated by the model is that, within the fault core, no contaminants were found. The contaminants rise through the high-permeability damage zone and cross
over the fault through the weathered granite. However, at depths where the water
changes direction slowly because of the fault barrier to horizontal ow, the contaminants
seem to be able to cross the fault. The explanation is that diffusion becomes
the dominant mode of transport at the point where the water moves at slow velocities.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ufs/oai:etd.uovs.ac.za:etd-05172013-122818 |
| Date | 17 May 2013 |
| Creators | Ndiweni, Cliford |
| Contributors | Prof GJ van Tonder |
| 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-05172013-122818/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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