Scoping Workshop Hydrogeological Aspects and Selection of Potential Sites C.J.H. Hartnady Umvoto

Ecological and Environmental Impacts of Large-scale

Groundwater Development in the Table Mountain Group

(TMG) Aquifer System

Scoping WorkshopScoping Workshop

Hydrogeological Aspects and Hydrogeological Aspects and Selection of Potential SitesSelection of Potential Sites

C.J.H. HartnadyC.J.H. Hartnady

UmvotoUmvoto

28 March 200328 March 2003

Scoping WorkshopScoping Workshop

Hydrogeological Aspects and Hydrogeological Aspects and Selection of Potential SitesSelection of Potential Sites

C.J.H. HartnadyC.J.H. Hartnady

UmvotoUmvoto

28 March 200328 March 2003 WRC Eco Project

WRC Eco Project

Objectives

Introduce TMG aquifer definitionsIntroduce TMG aquifer definitions

Define target zones for CCT ProjectDefine target zones for CCT Project

Discuss groundwater target type settingsDiscuss groundwater target type settings

Provide hydrogeological background to Provide hydrogeological background to scoping of potential impactsscoping of potential impacts

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TMG GroundwaterAquifers and Aquifers and AquitardsAquitards

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TMG Groundwater

Fractured-rock Fractured-rock aquiferaquifer

AquitardAquitard

Regolith (weathered-and-Regolith (weathered-and-fractured) aquiferfractured) aquifer

Aquifers and Mountain Aquifers and Mountain SpringsSprings

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GroundwaterUnconfined and Confined Unconfined and Confined AquifersAquifers•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 Confined (or artesian) aquifer – – Aquifer overlain by a low-permeability unit Aquifer overlain by a low-permeability unit (confining layer). A confined aquifer does (confining layer). A confined aquifer does not have a water table, only a not have a water table, only a potentiometric surfacepotentiometric surface which is defined by which is defined by water levels in boreholes under pressure.water levels in boreholes under pressure.WRC Eco Project

TMG Groundwater

Aquifers: Aquifers:

Confined / Confined / Unconfined Unconfined

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Radius of influence (rRadius of influence (ree))

for pumped wellfor pumped well

independent of abstraction rateindependent of abstraction rate (Q) (Q) depends only on:depends only on:

hydraulic conductivityhydraulic conductivity (K (K))

specific storage (Sspecific storage (Sss) )

durationduration (t) of abstraction(t) of abstraction

rre e == 1.5 (Kt/S1.5 (Kt/Sss))1/21/2

TMG Groundwater

rree

tt

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TMG GroundwaterHermanus Hermanus DevelopmentDevelopment

oo

oo

oooo

TMG Target Generation

Southern Target Region Southern Target Region Target Zone K (Kogelberg)Target Zone K (Kogelberg) Target Zone H (Hottentots-Holland)Target Zone H (Hottentots-Holland) Target Zone T (Theewaterskloof)Target Zone T (Theewaterskloof) Target Zone B (Brandvlei – south)Target Zone B (Brandvlei – south) Target Zone W (Wemmershoek)Target Zone W (Wemmershoek)

Northern Target Region Northern Target Region Target Zone B (Brandvlei – north?)Target Zone B (Brandvlei – north?) Target Zone V (Voelvlei)Target Zone V (Voelvlei) Target Zone A (Agter-Target Zone A (Agter-

Witzenberg ?)Witzenberg ?)

Southern Target Region Southern Target Region Target Zone K (Kogelberg)Target Zone K (Kogelberg) Target Zone H (Hottentots-Holland)Target Zone H (Hottentots-Holland) Target Zone T (Theewaterskloof)Target Zone T (Theewaterskloof) Target Zone B (Brandvlei – south)Target Zone B (Brandvlei – south) Target Zone W (Wemmershoek)Target Zone W (Wemmershoek)

Northern Target Region Northern Target Region Target Zone B (Brandvlei – north?)Target Zone B (Brandvlei – north?) Target Zone V (Voelvlei)Target Zone V (Voelvlei) Target Zone A (Agter-Target Zone A (Agter-

Witzenberg ?)Witzenberg ?)

CCT Feasibility & Pilot CCT Feasibility & Pilot ProjectProject

Target Zone Definition: Southern Area

FaultsFaults FracturesFractures

Target Zone Definition: Northern area

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TMG GroundwaterFluid Flow in FracturedFluid Flow in Fractured

RockRock

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Brandvlei (B) Target Zone: Northern area

Potential targets ?Potential targets ?

GoudiniGoudini

BrandvleiBrandvlei

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W Target Zone:Wemmershoek-Berg River scheme links

La Motte FaultLa Motte Fault

Klein Klein Drakenstein FaultDrakenstein Fault

ZSZS

ZS = ZS = Zachariashoek Zachariashoek SynclineSyncline

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H Target Zone: Steenbras-Palmiet scheme conjunction

KAKA

SSSS

SS = Steenbras SynclineSS = Steenbras SynclineKA = Kogelberg AnticlineKA = Kogelberg Anticline

Possible deep flow-path to submarine dischargePossible deep flow-path to submarine discharge

T Target Zone: Theewaterskloof scheme conjunction

RechargeRecharge

DischargeDischarge

Steenbras-BrandvleiSteenbras-BrandvleiMegafaultMegafault

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Voelvlei (V) Target Zone:Waterval Syncline and faults

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Thanks for Thanks for your your

attentionattention

Thanks for Thanks for your your

attentionattention

Ecological and Environmental Impacts of Large-scale Groundwater Development in the Table Mountain Group (TMG) Aquifer System

WRC Eco Project

City of Cape Town

Exploratory Phase Drilling: Typical Set-up

DWAF Core RigDWAF Core Rig

Exploratory Phase Drilling: Typical Set-up

Air Percussion RigAir Percussion Rigatat

HermanusHermanus

Exploratory Phase Drilling: Typical Set-up

Air Percussion RigAir Percussion Rigatat

HermanusHermanus

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) SuperaquiferOutcrop and subsurface Outcrop and subsurface

extentextent

TMG GroundwaterFluid Flow in FracturedFluid Flow in Fractured

RockRock

Landsat 5Landsat 5Band 347 (RGB)Band 347 (RGB)

compositecomposite

Hydrogeological Data Acquisition: 1:50 000 Digital Geology (CGS)

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