Transcript TMG Aquifer Feasibility Study

Ecological and Environmental Impacts of
Large-scale Groundwater Development in the
Table Mountain Group (TMG) Aquifer System
Scoping Workshop
Hydrogeological Aspects and Selection
of Potential Sites
C.J.H. Hartnady
Umvoto
28 March 2003
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Objectives
 Introduce TMG aquifer definitions



Define target zones for CCT Project
Discuss groundwater target type settings
Provide hydrogeological background to
scoping of potential impacts
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TMG Groundwater
Aquifers and Aquitards
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TMG Groundwater
Aquifers and Mountain Springs
Regolith (weathered-andfractured) aquifer
Fractured-rock
aquifer
Aquitard
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Groundwater
Unconfined and Confined Aquifers
•Unconfined aquifer – Aquifer overlain by an
unsaturated (vadose) zone or a surface water
body. Its upper surface is the water table
•Confined (or artesian) aquifer – Aquifer
overlain by a low-permeability unit (confining
layer). A confined aquifer does not have a water
table, only a potentiometric surface which is
defined by water levels in boreholes under
pressure.
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TMG Groundwater
Aquifers:
Confined / Unconfined
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TMG Groundwater
Radius of influence (re)
for pumped well
independent of abstraction rate (Q)
 depends only on:

hydraulic conductivity (K)
specific storage (Ss)
duration (t) of abstraction
re = 1.5 (Kt/Ss)1/2
re
t
TMG Groundwater
Hermanus Development
o
o
o
o
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TMG Target Generation
CCT Feasibility & Pilot Project

Southern Target Region
 Target Zone K (Kogelberg)
 Target Zone H (Hottentots-Holland)
 Target Zone T (Theewaterskloof)
 Target Zone B (Brandvlei – south)
 Target Zone W (Wemmershoek)

Northern Target Region
 Target Zone B (Brandvlei – north?)
 Target Zone V (Voelvlei)
 Target Zone A (Agter-Witzenberg ?)
Target Zone Definition: Southern Area
Faults
Fractures
Target Zone Definition: Northern area
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TMG Groundwater
Fluid Flow in Fractured Rock
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Brandvlei (B) Target Zone: Northern area
Goudini
Brandvlei
Potential targets ?
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W Target Zone:
Wemmershoek-Berg River scheme links
Klein
Drakenstein Fault
ZS
La Motte Fault
ZS =
Zachariashoek
Syncline
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H Target Zone:
Steenbras-Palmiet scheme conjunction
Possible deep flow-path to submarine discharge
SS
KA
SS = Steenbras Syncline
KA = Kogelberg Anticline
T Target Zone:
Theewaterskloof scheme conjunction
Recharge
Steenbras-Brandvlei
Megafault
Discharge
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Voelvlei (V) Target Zone:
Waterval Syncline and faults
Ecological and Environmental Impacts of
Large-scale Groundwater Development in the
Table Mountain Group (TMG) Aquifer System
Thanks for
your
attention
WRC Eco Project
WRC Eco Project
Exploratory Phase Drilling: Typical Set-up
DWAF Core Rig
City of Cape Town
Exploratory Phase Drilling: Typical Set-up
Air Percussion Rig
at
Hermanus
Exploratory Phase Drilling: Typical Set-up
Air Percussion Rig
at
Hermanus
Exploratory Phase Drilling:
V-notch yield measurement during air-lift test
Exploratory Phase Drilling:
Hermanus Magnetic Observatory site
Hermanus monitoring borehole:
Final construction and site rehabilitation
Table Mountain Group (TMG)
Superaquifer
Outcrop and subsurface extent
TMG Groundwater
Fluid Flow in Fractured Rock
Landsat 5
Band 347 (RGB)
composite
Hydrogeological Data Acquisition:
1:50 000 Digital Geology (CGS)
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