CASE STUDY Earth Observation Methodologies for Groundwater Exploration and Monitoring

CASE STUDY

Earth Observation Methodologies for Groundwater Exploration and Monitoring

Andiswa Mlisa

Hydrogeodesy Tutorial

13th WaterNet Symposium, 31 October – 2 November 2012

Outline

Introduction

Legal Framework

TMG Hydrogeology

Groundwater Development Stages and GeoInformatics

System

New Developments

IntroductionIntroduction

Introduction

13 % of the nation’s total water supply originates from

groundwater

Groundwater is a sustainable resource for bulk domestic

supply

Drought Preparedness (better than Relief)

Diversification of supply

Access to storage

Large evaporation-free storage

E.g. TMG: 2 to 3 order of magnitude higher than all

dams in Eden DM

Long residence time

Primary and shallow aquifers - 1 to 2 years

TMG in artesian basin - 10 000 years

Often most cost effective

URV usually < R2 / m3

Introduction

Legal Framework

National Water Act (1998) To achieve the sustainable use of water To achieve equitable access to water To achieve efficient and effective water use integrated management of all aspects of water resources delegation of certain management functions to a regional or

catchment level recognises water belongs to the nation for the benefit of all

“...Everyone has the right to have access to sufficient food and water….the state must take reasonable legislative and other measures, within its available resources, to achieve the progressive realisation of … these rights”

Section 27, SA Constitution

Legal Framework

Groundwater Development Groundwater Development Stages and GeoInformatics Stages and GeoInformatics

SystemSystem

Groundwater Development Stages

Conceptual

Reconnaissance

Pre-feasibility

Feasibility

Design and Implementation

Operations and Maintenance

GIS & EO in all stages

Ultimate aims include:

Ongoing database enhancement and availability

Automated search & access tools for distributed database

Web applications & public workspace

3D and 4D visualization and modeling

Focus areas:

Acquisition and conversion of data and metadata

Analysis and synthesis of data and metadata

Dissemination of data and metadata

Modern approach to groundwater exploration relies on interpretative overlays of great variety of different vector and raster data types (subsurface borehole logging to remotely-sensed geophysical or

satellite imagery) effective management of large volumes of diverse spatial data

Advantage of Remote Sensing + Geo-informatics “… investment for one crucial objective - detailed assessment of water resources - potentially serves many others. The geological information applies equally to assessment of other physical resources. The same data and hardware serve a wide range of agricultural and environmental surveys …”

S.A. Drewry & M.E. Andrews Deller

Conceptual & Reconnaissance Stages – Data acquisition

Topography Cadastral Hydroclimatology data Hydrological data Regional geology mapping Regional geophysics data Ecological data Aerial and Satellite imagery

contours DEM

Slope Aspect

1:50 000

scale

mapping

(CGS)

• min. = 198 mm/a

• max. = 3404 mm/a

Strong dependence of MAP on elevation (Orographic control of rainfall)

Rain shadow effects east of mountains

Needed to model groundwater recharge to TMG

Statutory protected arease.g., Nature reserves

Sensitive ecological arease.g., Wetlands

Classification mapse.g., NBI Vegetation

Satellite Imagery

Landsat7

ETM

SPOT 4 / 5

Aerial Photos

Information Sources: National Groundwater Database Hydrocensus Other projects

Type of Information: Borehole yield Borehole construction Geology information and aquifer

used Chemistry Water use Annual abstraction of groundwater Discharge of springs and rivers

Pre-Feasibility & Feasibility – Data analysis and synthesis

Fracture traces – fluid flow in fractured rock

Directional analysis and fracture connectivity

Vegetation indices, derived from Satellite Imagery Analysis

GIS-based modelling

Groundwater target-site selection, based on

Hydrogeological criteria

Ecological criteria

Normalised Difference Vegetation Index (NDVI)

Application:

Vegetation (green)

No Vegetation (brown)

Two spectral bands used

NDVI = (NIR–red) / (NIR+red)

Landsat ETM = (4-3) / (4+3)

Tasseled Cap Image

Application:

Vegetation (green)

Bare rock / soil (red)

Water bodies / wetlands (blue)

Six spectral bands used

Three different formulae

Three output raster objects:

Greenness Brightness Wetness

Change Vector AnalysisAnalyses difference between two or more datesNumber of bands and bands used can vary

Methodology: Image calibrationMagnitudeDirectionReclassification

Application:Vegetation anomalies – groundwater dependency of

ecosystems

CAGE Study

Compared with February 1998 image

RechargeRecharge

Discharge

Steenbras-BrandvleiSteenbras-BrandvleiMegafaultMegafault

Air Percussion Rig

Hermanus Gateway wellfield

Wellfield pumping rates at 10l/s – 30l/s

Licensed for 1.5Mm3/a

Water Use Licence

Application

Target sites Landowners Access Land use

Design and Operations – Data analysis and synthesis

Wellfield design and operations

Storage Model

Licence conditions

Numerical Model

Continuous monitoring

Vegetation indices, derived from Satellite Imagery Analysis

In-situ monitoring

Storage Model MethodologyModel Input Parameters

Source Detail

Weltevrede - Lake MentzBidouw - WeltevredeCeres - BidouwRietvlei - CeresSkurweberg - RietvleiGoudini - SkurwebergCedarberg - GoudiniPakhuis - CedarbergPeninsula - PakhuisPeninsula - selected others (basement)FaultsCross-sections

Rock compressibility

Domenico and Schwartz (1990)

3.3 x 10-10 Pa-1 to 6.9 x 10-10 Pa-1

PorosityTalwani and Acree (1985); Blikhuis borehole data

0.005 - 0.163

Specific storageCalculated from rock compressibility and porosity

3.0E-06 to 7.0E-06

Formation and area specific:Peninsula: 700 m (KGB), 1100 m (THK, WEM)Skurweberg: 200 m (KGB), 300 m (THK)

Contacts for aquifer base and top

True thicknessField data and literature

1:250 000 geological map

Controls

1:250 000 and 1:50 000 geological maps

Storage Model Results

Peninsula Peninsula FormationFormation

aquifer baseaquifer base

Peninsula Peninsula FormationFormationaquifer topaquifer topArea Rock Volume Pore Volume

(km2) (Mm3) (Mm3)

Unconfined portion 474.53 297 314 14 866

Confined portion 1 206.42 1 154 373 57 719

Whole aquifer 1 680.95 1 451 687 72 585

Aquifer

Peninsula Formation

~ 430 Mm3

Storage Model GIS Model Advantages and limitations of using a digital GIS storage model: Physically correct in terms of obtaining the rock volume (+)Possible to obtain a visually descriptive spatial overview of the aquifer geometry (+)Apparent thickness of the aquifer can be more accurately determined (+)Only as accurate as the scale of the input data (-)Exact depth of contacts cannot be accurately determined at fault zones (-)

Groundwater Reserve

DAGEOS Case Study

Groundwater Reserve

Results of Reserve Determination

PES

Resource

Reserve

Resource UnitWater Quantity

Recharge Baseflow GW-Use Stress IndexMillion m3/a Million m3/a Million m3/a   Class

1 – Unconfined Ope 34.3 14.1 0.45 0.02 A2 – Confined Ope 19.7 0.00 0.00 0.00 ATotal 34.3 14.1 0.45 0.02 A

Resource Unit

Classification Resource Evaluation

Present Proposed Recharge Baseflow GW-Use

Quant. Qual. Quant. Qual. Million m3/a Million m3/a Million m3/a

1 A B C B 34.3 14.1 0.452 A A D B 19.7 0.0 0.00

Total A A D B 34.3 14.1 0.45

Resource Unit

Resource Evaluation Reserve ComponentsAllocable

Groundwater

Recharge Baseflow GW-Use BHN EWR Reserve Class

1 34.3 14.1 0.45 0.02 14.1 19.7 9.92 19.7 0.0 0.00 0.00 0.0 19.7 14.8

Total 34.3 14.1 0.45 0.02 14.1 19.7 14.8

DAGEOS Case Study

In-situ Monitoring Components

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

2007-2008 CVA

2009-2010 CVA

Time Series Analysis

Ecological Monitoring

Effective at mapping potential perennial

groundwater discharge areas

Regional monitoring

Provides baseline monitoring information

prior to abstraction and

Distinguish between climatic and wellfield

induced change

3 – Tiered system: 1. Long term monitoring

2. Early Warning

2. Early Warning

3. Emergency Response

New developments - New developments - hydrogeodesyhydrogeodesy

TrigNet 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 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

TMG & S.Cape Geodetic Monitoring

Gateway wellfield and HMO

SANSA Space ScienceSANSA Space Science

cGPS 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 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 Displacement

an average movement of 19.3 mm/yr Northwards and 16.2 mm/yr Eastwards

HNUS Vertical Displacement

downward motion of ~3.0 mm/yr

HGW1 Vertical Displacement

Upward motion of ~4.5 mm/yr Apparent vertical motion roughly equal to HNUS, but in opposite

direction – due to fault location?

Short-term scale analysis

HGW1 & HGW2HGW3

end pumping

HGW3 to HNUS Vertical Displacement

clear downward movement followed by an upward movement in response to a pump switch off - Noordbergum effect (reverse water-level fluctuation)?

Thank youThank you