Gateway Wellfield project, Gateway Wellfield project, Hermanus, South Africa: Hermanus, South Africa: Implementation, system Implementation, system

testing, aquifer monitoring testing, aquifer monitoring andand

hydrogeodetic observation hydrogeodetic observation

Chris Hartnady,1 Andiswa Mlisa,1 Eric Calais,2

Richard Wonnacott,3 Helen Seyler1

11 Umvoto Africa (Pty) Ltd, Muizenberg, South Africa22 EAS Dept, Purdue University, West Lafayette, Indiana, USA

33 CD:NGI, Mowbray, South Africa

AfricaArray 2011 workshop, AfricaArray 2011 workshop, University of the WitwatersrandUniversity of the Witwatersrand22 Nov 201122 Nov 2011

Hermanus Groundwater Project:Hermanus Groundwater Project:Implementation & System TestingImplementation & System Testing

CCTCCTHNUSHNUS

Table Mountain Group Table Mountain Group palaeogeographypalaeogeography

Deposition of TMGDeposition of TMG at at mouth of Amazon-mouth of Amazon-scale river system scale river system draining southern draining southern front of vast front of vast Famatinian-Taconic Famatinian-Taconic mountain belt in mountain belt in collision zone collision zone between Gondwana between Gondwana and Laurentia and Laurentia

TMG - Amazon delta analogueTMG - Amazon delta analogue

Until 1976 single schemes in each town:Surface water use (dams) in Fisherhaven and Voelklip

Groundwater use (boreholes or small wellfields) in Hawston, Onrus, Hermanus

Since 1976 DeBos Dam as source for all towns in Greater Hermanus AreaPreviously used schemes abandoned

Overstrand Water SupplyOverstrand Water Supply

Overstrand Groundwater Overstrand Groundwater InvestigationInvestigation

Phase A – Inception (2001/2002)Phase B – Detailed Design &

Implementation (2002 – 2006)B1 – Wellfield Development at GatewayB2 – Monitoring programmeB3 – Hydrogeological ReconnaissanceB4 – License Application

Phase C – Conjunctive Water Resource Planning (2006 onwards)

Hermanus GeologyHermanus Geology

Hermanus Geo-profileHermanus Geo-profile

Peninsula Peninsula Aquifer:Aquifer:High confining High confining pressure, high pressure, high yielding yielding fracturesfractures

Wellfield pumping rates: 10 – 30 l/sLicense:1.5 Mm3/a

Gateway Wellfield

Monitoring Boreholes GWE07, GWE08, GWE09 and GWE10

Monitoring Wellpoints WP1 – WP4

Existing Production Borehole GWP01

New Production Borehole GWP02

New Production Borehole GWE06

Gateway ChallengesGateway Challenges

Management challenges in HermanusAvoid seawater intrusionAvoid dewatering confined aquiferAvoid unacceptable impact in ecologically sensitive recharge zone

Appropriate technology to address challenges??

Gateway steady-state modelGateway steady-state modelPosition of modelled Hermanus Fault

NE

Alice Dodman, 2008Alice Dodman, 2008

Limits pushed ?Limits pushed ?

Pushing limits of equipment & technical capabilities allows successful management in a potentially unmanageable environment (saline intrusion, environmental concern & opposition)

Monitoring system allows aquifer limits to be pushed

A 7-year human push…resulted in 20-year license awarded, an accepted aquifer management strategy, and handing over wellfield to municipality

Aquifer Monitoring FrameworkAquifer Monitoring Framework

Framework for Sustainable UseFramework for Sustainable Use

SCIENCE:Water resourceSOCIETY:

The people involved

Operational data:Pump test observation

MONITORING

Water levels / flows

Environmental impact

Available aquifer yield

BotanicalTheoretical means:Modelling

Onrus Monitoring Committee

DWA & CMA & DEA&DP

WSA & WSP WUAI&APs

Sustainable Management of Gateway Wellfield & Peninsula Aquifer

Monitoring ProgrammeMonitoring Programme

Based on Hydrocensus (2003)Spatial and time distribution of

Rainfall Stream flowWater level (Surface and Groundwater)Water qualityEcological conditionWater use and abstraction

Monitoring overviewMonitoring overviewMonitored point

Water level

EC Flow rate

pH Chemical analysis

Isotopes

3 x production

* *

6 x Peninsula monitoring

N/A

3 x Skurweberg monitoring

N/A x

6 x shallow WP

N/A x

1 x other major GW user

GW dependent ecosystems

x

x x

Three–tiered systemThree–tiered system

Long term monitoring

Early warning system

Emergency response

3–tiered system3–tiered system

Monitoring point

Water level

EC Flow rate

pH Chemical analysis

Isotopes

3 x production

Monthly to ad hoc

Every second

Out of acceptable range? Immediate sms alarms

Checked daily

Every 30 minutes

Transmits to internet every hour

Real-time monitoring Real-time monitoring

Enables Overstrand to show to DWA, DEA&DP, and I&AP’s concerned with potential environmental impact, that Peninsula aquifer targeted at Gateway can - and is being - managed sustainably

Has therefore become key aspect of licence conditions

Is essential for sustainable aquifer management in such sensitive environment

Water-Level Monitoring (2003-Water-Level Monitoring (2003-2011)2011)

GWE06 – WL & EC record (2010-GWE06 – WL & EC record (2010-2011)2011)

Hydrogeodetic ObservationHydrogeodetic Observation

Precedent case study:Precedent case study: Mesquite, Nevada Mesquite, Nevada

Mesquite settingMesquite setting

South African TrigNet systemSouth African TrigNet systemNetwork of permanent continuously operating GPS

(cGPS) base stationsDistributed throughout South Africa at approximately

200 – 300 km spacingAll stations record 1-second epoch data on both

GPS frequencies (L1 and L2) through geodetic-standard choke ring antennas

21 stations stream data continuously to TrigNet control centre in Chief Directorate: Surveys and Mapping

Available within 30 minutes after each hour for 24 hours a day

TrigNet station distributionTrigNet station distribution

HNUSHNUS

Gateway wellfield and HMOGateway wellfield and HMO

Hermanus Magnetic Hermanus Magnetic ObservatoryObservatory

Gateway and HMO cGPSGateway and HMO cGPS

Acquisition of InstrumentsAcquisition of InstrumentsAshtec eBox

Trimble Zephyr antenna

Construction and EstablishmentConstruction and EstablishmentPillar to be rigid and well anchored to borehole plinth

Construction and EstablishmentConstruction and EstablishmentMonument and antenna installation at wellheads (Oct-Nov 2008) for measurement of

surface subsidence during groundwater abstraction

1st project 1st project workshopworkshop

field inspectionfield inspection(Jan 2009)(Jan 2009)

Data HandlingData Handling

Telemetry systemCell phone communication Private Network (machine to machine)remote downloading of dataremote access to site

Data handling challenges and possible solutionsData record at 1sec interval - 77MB per station per dayCompression function not workingTransfer of data site-Umvoto-AIMSCollaboration with Centre for High Computing for data transfer?Collaboration with CSIR-SAC for data mirroring / backup and

transfer?Data reduction process from 1sec-30sec

HY 2008-09 Test PumpingHY 2008-09 Test Pumping

HGW1 & HGW2HGW3

Gateway and HMO cGPSGateway and HMO cGPS

HGW1-HGW2 HGW1-HGW2 ResultsResults

end pumping

No observed signal

HGW3 to HNUS ResultHGW3 to HNUS Result

end pumping

?

??

?

Complex end-pumping signal, in N component only?

Unexplained blips in E component

HGW3 to HNUS ResultsHGW3 to HNUS Results

end pumping

Initial (~10 mm) response in opposite direction to expected uplift, possibly related to poro-elastic deformational response in overlying aquitard (Noordbergum-Rhade effects)

Recovery uplift (~20 mm) linked to ~15 m rise in Peninsula aquifer water-level?

Restoration to zero?

AcknowledgementsAcknowledgements The Overstrand Municipality, in particular town engineer,

Mr Stephen Muller, for generous co-operation

The Department of Land Affairs & Rural Development (Chief Directorate: National Geospatial Information) for technical support and assistance related to TrigNet and additional GPS hardware

The WRC and Dr Shafiek Adams for funding support

The Department of Science and Technology for additional funding support

Prof. Hans-Peter Plag and IGCP565 for support to attend Johannesburg workshop