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Global Navigation Satellite System Methodology for Groundwater Resource Assessment, Gateway Wellfield, Hermanus. Andiswa Mlisa , Chris Hartnady and Sheila Imrie Umvoto Africa (Pty) Ltd, Muizenberg, South Africa www.umvoto.com. 5 th IGCP 565 Workshop, 29 – 30 October 2012, Johannesburg. - PowerPoint PPT Presentation
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Global Navigation Satellite System Global Navigation Satellite System Methodology for Groundwater Resource Methodology for Groundwater Resource
Assessment, Gateway Wellfield, Assessment, Gateway Wellfield, HermanusHermanus
Andiswa Mlisa, Chris Hartnady and Sheila Imrie
Umvoto Africa (Pty) Ltd, Muizenberg, South Africa
www.umvoto.com
5th IGCP 565 Workshop, 29 – 30 October 2012, Johannesburg
Background & OutlineBackground & OutlineOverstrand Municipality investigating groundwater potential of Greater
Hermanus Area, for augmentation to supply
OutlineOutline:
Global Navigational Satellite Systems (GNSS) in South Africa
Table Mountain Group (TMG) hydrogeology at the Gateway wellfield, Hermanus
Geodetic Monitoring at Gateway wellfield, Hermanus
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
Groundwater InvestigationGroundwater InvestigationPhase 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)
Global Navigational Satellite Global Navigational Satellite Systems (GNSS) in South AfricaSystems (GNSS) in South Africa
TrigNet station distributionTrigNet station distribution
HNUSHNUS
Network of permanent continuously operating GPS (cGPS) base stations
Distributed throughout South Africa
All stations record 1-sec epoch data on both GPS frequencies (L1 and L2)
South African TrigNet systemSouth African TrigNet systemTrigNet system was developed as a national control
survey network used for land reform projects with the following as spinoff applications: Serve as a baseline geodetic datum; Track crustal movements to millimeter per year
precision; Contribute to the understanding of plate tectonics and
earthquake hazards; Provides a convenient platform for developing a new
space and ground-based system for monitoring the seasonal fluctuations in aquifer storage through detection of associated small deformations; and
Has applications in ionospheric physics, meteorology and atmospheric profiling
Table Mountain Group (TMG) Table Mountain Group (TMG) hydrogeology at the Gateway hydrogeology at the Gateway wellfield, Hermanuswellfield, Hermanus
Hermanus Geological SettingHermanus Geological Setting
Hermanus Geological SettingHermanus Geological Setting
Gateway wellfield and HNUSGateway wellfield and HNUS
SANSA Space ScienceSANSA Space Science
Peninsula aquifer has high confining pressure, artesian conditions and fracture dominated flows
Wellfield pumping rates at 10l/s – 30l/s
Licensed for 1.5Mm3/a
Gateway Gateway wellfieldwellfield
Monitoring Monitoring ComponentsComponents Water-level in fractured rock
aquifer Water-level in primary alluvium
aquifer Water quality in fractured rock
aquifer Spring and surface-water flow
rate and quality Rainfall, atmospheric temperature
and air-pressure Record of abstraction rates and
volumes
Effective Stress Effective Stress ConceptConcept
(1) The initial position of the piezometric surface in the confined fractured aquifer;
(2) The change in the piezometric surface in the confined aquifer due to the cone of depression (drawdown) around the pumping well;
(3) The resultant effect of skeletal compression on the aquifer material; and
(4) The elastic rebound of the aquifer when pumping stops and water levels recover.
Geodetic Monitoring at Geodetic Monitoring at GatewayGateway
Gateway and HNUS cGPSGateway and HNUS cGPS
cGPS at Gateway wellfieldcGPS at Gateway wellfield Monument and antenna installation at wellheads (Oct-Nov 2008) for
measurement of surface subsidence during groundwater abstraction Precise positions; 30 second dual frequency data Relative to IGS stations
HGW3 HGW1
HNUS Horizontal DisplacementHNUS Horizontal Displacement
An average motion of 19.6 mm/yr Northwards and 16.2 mm/yr Eastwards.
The NU-ITRF2005 solution indicates a model NU velocity at the HNUS site of 18.8 mm/yr Northwards and 16.7 mm/yr Eastwards, corresponding to motion of 25.2 mm/yr towards azimuth (Altamimi et al., 2007).
HGW1 Horizontal DisplacementHGW1 Horizontal Displacement
an average movement of 19.3 mm/yr Northwards and 16.2 mm/yr Eastwards
HNUS Vertical DisplacementHNUS Vertical Displacement
WMRS error 11 mm compared to 2 mm in the horizontal displacement downward motion of ~3.0 mm/yr
HGW1 Vertical DisplacementHGW1 Vertical Displacement
Upward motion of ~4.5 mm/yr for HGW1 Apparent vertical motion is roughly equal to that at HNUS, but
opposite in direction – due to fault location?
HGW1 Vertical Displacement vs HGW1 Vertical Displacement vs PumpingPumping
HGW1 Vertical Displacement vs Water HGW1 Vertical Displacement vs Water LevelLevel
HGW1 Vertical Displacement vs RainfallHGW1 Vertical Displacement vs Rainfall
HGW1 Vertical Displacement vs HGW1 Vertical Displacement vs PressurePressure
All Stations Relative to HNUS Vertical All Stations Relative to HNUS Vertical DisplacementDisplacement
HGW1 trends upwards relative to HNUS, HGW2 seems to trend downwards, and HGW3 remains fairly stable
Summary ResultsSummary Results
horizontal displacements at Hermanus GPS stations are closely aligned with calculated horizontal velocity components of Nubia plate relative to ITRF;
vertical displacements showed varying long-term trends (upwards at HGW1, downwards at HGW2 and flat at HGW3) with high frequency of peaks and troughs that correlate between stations
vertical displacement showed no clear link to pumping or atmospheric phenomenon at daily (one session per day) time-scale;
Way forward: short-term scale Way forward: short-term scale analysisanalysis
HGW1 & HGW2HGW3
HGW3 to HNUS Horizontal DisplacementHGW3 to HNUS Horizontal Displacement
WRMS values on the order of 1 mm – 2 mm, compares with relative to global stations and daily processing
end pumping
HGW3 to HNUS Vertical DisplacementHGW3 to HNUS Vertical Displacement
WRMS value of 3 mm compared to 11 mm on daily & relative to global station
clear downward movement followed by an upward movement in response to a pump switch off - Noordbergum effect (reverse water-level fluctuation)?
RecommendationsRecommendations
Further processing of shorter time steps Another site on same fault block as HNUS would be
potentially useful An experimental system using a combination of land-
based observations (viz., GPS, and high-precision microgravity measurements) and complementary satellite gravity (e.g., GRACE) and satellite radar (e.g., InSAR)
Use of analysis results from study to update hydrogeological numerical models of Hermanus area.
Wider “Natural Laboratory” Wider “Natural Laboratory” conceptconcept
Capacity BuildingCapacity Building Workshops
2009, SANSA Space Science, Hermanus 2010, African Institute for Mathematical Sciences, Cape Town 2011, University of Johannesburg, co-located with CAG 23
Conference presentations
Thank YouThank You