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Groundwater Models A COMMUNITY GUIDE TO BETTER UNDERSTANDING

Lisa Robins, David Freebairn & Andrew Sedger

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Written by Lisa Robins, David Freebairn & Andrew Sedger

Published by Murray-Darling Basin Commission

Level 5, 15 Moore StreetCanberra ACT 2600Telephone: (02) 6279 0100from overseas + 61 2 6279 0100Facsimile: (02) 6248 8053from overseas + 61 2 6248 8053Email: [email protected]: http://www.mdbc.gov.auISBN: 1 876830 45 X

Cover photo: Copyright NSW Agriculture

© 2003 Murray-Darling Basin Commission

This work is copyright. Graphical and textual information in the work (with the exception ofphotographs and the MDBC logo) may be stored, retrieved and reproduced in whole or in part,provided the information is not sold or used for commercial benefit and its source (Murray-Darling Basin Commission, Groundwater Models—A community guide to better understanding)is acknowledged. Such reproduction includes fair dealing for the purpose of private study,research, criticism or review as permitted under the Copyright Act 1968. Reproduction for otherpurposes is prohibited without prior permission of the Murray-Darling Basin Commission or theindividual photographers and artists with whom copyright applies.

To the extent permitted by law, the copyright holders (including its employees and consultants)exclude all liability to any person for any consequences, including but not limited to all losses,damages, costs, expenses and any other compensation, arising directly or indirectly from usingthis report (in part or in whole) and any information or material contained in it.

The contents of this publication do not purport to represent the position of the Murray-DarlingBasin Commission. They are presented to inform discussion for improved management of theBasin’s natural resources.

MDBC Report No. 02/03

Source: Arthur Mostead

Contents

GROUNDWATER MODELLING CONCEPTS

Can groundwater modelling help you?................................................................................................. 2

What is groundwater?........................................................................................................................... 3

Why is groundwater important? ........................................................................................................... 5

Why model groundwater? .................................................................................................................... 6

What is a model? .................................................................................................................................. 7

Data quality and availability ................................................................................................................... 8

MAKING A SOUND INVESTMENT

Choosing the ‘right’ model.................................................................................................................... 10

Types of models.................................................................................................................................... 11

Choosing the ‘right’ modeller................................................................................................................ 12

Models are a team effort....................................................................................................................... 12

UNDERTAKING A SUCCESSFUL STUDY

The scoping study................................................................................................................................. 14

Model development .............................................................................................................................. 15

The conceptual model .......................................................................................................................... 16

Model reliability ...................................................................................................................................... 17

Overseeing the study ............................................................................................................................ 18

Reviewing the model............................................................................................................................. 18

Summary............................................................................................................................................... 19

Glossary................................................................................................................................................. 20


Catchment communities and naturalresource managers come across many‘what if’ questions when they areplanning and setting priorities for landand water actions in their catchments.For example:

• What will happen to the spread of dryland salinity if we plant 50 hectares of pine trees?

• What will happen to streamflow if we extract more groundwater from bores?

• What will happen to salt loads in the river ifwe expand irrigated agriculture in the region?

Groundwater models can help you answermany of these ‘what if’ questions.

A model can be simple or complex, dependingon the question you need to answer. Morecomplex questions will require a more detailedunderstanding of groundwater systems, andtherefore a more detailed model, and most likely more data.

While communities and resource managersmay never see or use the models themselves,they use the results generated by groundwatermodels in decision-making processes for theircatchment. Increasingly, these information

users need to have a better understanding of the capabilities and limitations of models.

The Murray-Darling Basin Commission usesgroundwater models to inform its priorities and to measure the potential impacts of landand water management actions in the Basin.Groundwater models were used to produce ‘The Salinity Audit of the Murray-Darling Basin’(MDBC 1999), which outlines predictions ofdryland salinity for the years 2020, 2050 and2100. The results of these predictions underpinthe 15-year ‘Basin Salinity ManagementStrategy’ (MDBC 2001).

This handbook gives you, as catchmentcommunities and resource managers, an insight into groundwater modelling. It looks at:

• Groundwater modelling concepts• Making a sound investment in groundwater

modelling• Undertaking a successful groundwater

modelling study.

A more comprehensive technical guideline byMiddlemis et al. (2001) entitled ‘Groundwaterflow modelling guideline’ is available from theMurray-Darling Basin Commission.

2

Can groundwater modelling help you?

The Murray-Darling Basin Commission uses

groundwater models to inform its priorities and to

measure the potential impacts of land and water

management actions in the Basin.

The Murray-Darling Basin Commission uses

groundwater models to inform its priorities and to

measure the potential impacts of land and water

management actions in the Basin.



3

What is groundwater?GROUNDWATER MODELLING CONCEPTS

Groundwater is the water found

under the ground that supplies wells,

bores and springs.

When rain falls to the ground, the water doesnot stop moving. Some of it flows along thesurface into streams or lakes, some of it isused by plants, some evaporates andreturns to the atmosphere, and some movesthrough the soil beyond the zone whereplant roots can use it—this water eventuallybecomes groundwater.

Groundwater moves through—and is stored in—the spaces in soil, sand and rock,known as aquifers. It moves at differentspeeds and in different directions, dependingon the type, shape and materialcharacteristics of the aquifer. Groundwatermay channel quickly in ancient streambedsbeneath the surface or move slowly throughwater-holding rock layers.

The catchments of groundwater systems areoften very different to those of surface watercatchments.

For example, the Murray River Catchment isvery different in size, shape and behaviour tothe Murray Groundwater Basin, although thetwo systems are closely connected (see mapon page 4). In surface catchments, waterflows in the direction of the slope whereasgroundwater flow often follows in the directionof tilting rock layers.

Groundwater systems tend toward a generalstate of balance, where, over time, naturalinputs (rainfall going into the soil) roughly equalnatural outputs (discharge back to the surface).

Human activities, such as groundwaterpumping, irrigation, land clearing andcropping, can upset this balance. It can leadto groundwater shortages, if the rate of useexceeds the rate of filling, and other problems,such as waterlogging or salinisation, if the rateof filling exceeds the rate of use.

Source: ‘Trees, Water and Salt.’ © 2002 Joint Venture Agroforestry Program

A good analogy for a groundwater system is to think of it as a half-full bathtub with a small plughole. Water can only come in through the tap or out through the plughole. If water comes infaster than it leaves, the tub eventually overflows. If water leaves faster than it enters, the tub soonempties. Groundwater systems behave in a similar way.

4

Lake Victoria

SOUTH AUSTRALIA

0 100 200 km

ADELAIDE◆

CANBERRA◆

Murray Groundwater Basin

Great Artesian Groundwater Basin (part within the MDB)

Darling River Groundwater Basin

Areas of Fractured Rock Aquifers

Murray-Darling River Basin (surface)

G R O U N D WA T E R R E G I O N S O F T H E M U R R AY- D A R L I N G B A S I N

Source: Murray-Darling Basin Commission


Groundwater is an important resource

for humans and for the environment.

Because it is often closely connected

with surface water, it may be the only

source of flow for streams during dry

periods and plays a crucial role in

maintaining the health of rivers.

Groundwater can be found in varying quantities

and at varying depths, from just a few metres

below the surface to many hundreds of metres

deep. When extracted through bores,

groundwater provides a valuable source of

irrigation for crops and pastures, as well as a

supply of water for livestock, towns and

industry.

The quality and quantity of groundwater is

highly variable across Australia. Sometimes

groundwater is fresh; sometimes it is salty.

It can also be contaminated with nutrients or

pollutants. The quality of the groundwater is

closely related to the geology in which it exists

and the origin of the water. In the large regional

alluvial aquifers, bores remote from recharge

may have to pass through salty layers of

groundwater to reach a freshwater layer below.

Human activities can affect the quality of

groundwater through changing the chemistry

of water entering the aquifer. This can occur

through air pollution or poor management

practices in agricultural, industrial and urban

areas.

While groundwater can be a valuable resource

when it is good quality and ‘in balance’, it can

pose a threat if it is ‘out of balance’, salty or

otherwise contaminated.

Excessive groundwater can move salt to the

surface, resulting in salinity, which in turn can

damage agricultural industries, infrastructure like

fences, roads and buildings, and the

environment. Groundwater of poor quality can

also contaminate good quality surface water

supplies—and affect the plants, animals and

people that depend on it.

Proper use and management of groundwater

is therefore critical to ensure the quality and

sustainability of the resource.

Why is groundwater important?




fences, roads and buildings, and the environment.




fences, roads and buildings, and the environment.

5



A groundwater model helps us understand

groundwater systems, and explore or predict

changes at some time in the future.

A groundwater model helps us understand

groundwater systems, and explore or predict

changes at some time in the future.

In order to make the best decisions

about land and water management

actions and investment in

catchments, communities and

resource managers want answers to

the ‘what if’ questions like those

discussed earlier.

As groundwater plays such a central role in

the movement of water in catchments, we

need a good understanding of groundwater

systems to answer these sorts of questions.

But as we cannot see groundwater systems,

we use a model to ‘paint a picture’ of what they

look like and how they behave in different

conditions. This enables us to predict what

might happen if we change any of the inputs,

outputs or other factors affecting such systems.

We can use a groundwater model to work

out, for example, if clearing an area of land

will lead to a rise in the watertable and cause

waterlogging of surrounding areas. We may

want to know how long it will take before

pollutants will pass through a contaminated

aquifer or what will happen to streamflow if

additional water is taken from a nearby

aquifer.

Groundwater models help us to build a

better understanding of the relationship

between natural resources and human

activities—for example, how weather

variability, land clearing, rotational grazing,

high stocking rates and irrigation affect

groundwater levels. Understanding these

relationships will enable us to make better

decisions about how to manage human

activities in the catchment.

Why model groundwater?

6


Source: John Baker

A model is a tool that helps us

predict changes in a particular system

before they happen. Models are used

for all sorts of purposes: from trying

to predict the weather, to trying to

predict the stock market.

A loan calculator used by your bank is agood example of a model. The bank usesthis model when you apply for a loan in orderto predict whether you will be able to affordto pay the loan back. The model considershow much money you earn through salaryand investments (inputs), and how muchmoney you spend through expenses, taxes,etc. (outputs). Calculations are then used totally up how much you will need to pay ininterest and therefore how much you areable to safely borrow.

A groundwater model is much the same. It also has inputs (rain, irrigation) and outputs(bore water, discharge into streams), whileusing mathematics to calculate changes tothe system. For example, a calculation maybe used to account for the fact that waterenters a groundwater system faster than itleaves. The model then predicts what willhappen to the extra water.

Groundwater models are generally made and operated by experts in a field of scienceknown as hydrogeology (‘hydro’ meaningwater and ‘geo’ meaning earth). This is afield that specialises in understanding theinteraction of water and geology, and relieson the application of well-understoodphysical principles.

In order to construct a groundwater model,hydrogeologists try to understand as muchas possible about the groundwater systemso they can describe and quantify it. Theycollect information, take measurements andlook at relationships between different partsof the system.

The drilling of bores allows us to collectinformation (also referred to as ‘data’) like thedepth of groundwater, its quality and the kindof material through which it is moving, suchas the soil or rock type. Modellers also usedata about rainfall, evaporation, waterextraction, irrigation and land use. In general,the more data collected (both in space andover time), the more accurate the model.

However, hydrogeologists are often required tomodel groundwater systems without completedata. In every case a mix of skill, experienceand good judgement is needed. The resultingmodel is our best bet assessment of allavailable information and experience at thetime (which will improve as we learn more).

What is a model?GROUNDWATER MODELLING CONCEPTS

Groundwater models aregenerally made andoperated by experts in a field of science known as hydrogeology (‘hydro’meaning water and ‘geo’meaning earth).

7

The results produced by a

groundwater model are only as good

as the data that underpins the model.

Like the saying goes: rubbish in = rubbish

out. The quality and availability of data, such

as rainfall records, geological surveys, soils

and land use maps, is extremely varied

throughout Australia.

The limitations of data quality and availability

may determine the type of modelling that

can take place. You may need to revise your

modelling expectations on the basis of

inadequate data. Some of the more

complicated and expensive modelling

approaches may not be feasible or, in some

instances, you may not be able to undertake

any modelling at all!

A review of data availability at the beginning

of a groundwater project may point to critical

gaps in information. You may need to

allocate resources to collect additional data

before modelling can commence. Some

data may be available but will require

significant manipulation to get it into a form

suitable for modelling purposes.

Compiling data often consumes a large part

of the modelling effort. These data sets

should be treated as a valuable asset.

Because detailed data is not available

uniformly across the country, we can

sometimes transfer or interpret it from a

similar environment. A framework called

‘catchment classification’ has been adopted

to provide a consistent approach to

describing groundwater flow systems.

Regional maps and information packages

on management options for individual

groundwater flow systems are available

for all catchments in the Murray-Darling

Basin (see www.ndsp.gov.au and

www.nlwra.gov.au/atlas). This information

will help you define your information and

data needs.

Data is collected and owned by many

organisations, particularly government

departments. Accessing data and dealing

with associated intellectual property and

copyright issues can be a major hurdle in

any modelling project and must be

addressed well before any modelling can

get underway.

Ideally, you should learn more about your

groundwater system(s) as your data sets

grow. It is therefore important that your

model is flexible enough to be expanded at

a later date, whenever new data becomes

available. Flexibility is also important for

models used for long-term catchment or

groundwater system management.

Data quality and availability

8


Compiling data often

consumes a large

part of the modelling

effort.



9

GROUNDWATER FLOW SYSTEMS OF THE MURRAY-DARLING BASIN

intermediate flow systems

local flow systems

regional flow systems

water bodies

The model that’s ‘right’ for you will

depend on many factors—some of

the key ones are accuracy, timeframe

and resources available. An off-the-

shelf modelling code from which to

base your model may not exist for

your particular circumstances.

A new model, or a modified existing

model, may be required to suit

your needs.

One of the first things you will need to

decide when choosing a model is the level of

accuracy that is required. Are you just

scoping a problem or looking for a refined

result? The capacity for achieving an

accurate result is highly dependent upon the

quality of available data inputs like soils,

landform, groundwater levels and geology.

You may discover that some data collection

needs to take place to enable the level of

modelling you have in mind.

As a rule of thumb, it’s usually better to go

with as simple a model as possible that

adequately fulfills your needs. It’s like buying

a car—don’t buy a Jaguar when a Mini will

do the job. More complex models are likely

to require more detailed inputs, which means

more time and resources. If a model is not

transparent and its workings cannot be

explained in relatively simple terms, then it

might be overly complex—or you might be

buying a lemon.

A note of caution though, a simple model is

not necessarily a valid model. Underlying all

models is a range of assumptions that are

used to simplify reality down to the level that

it can be represented by mathematical

equations. If these assumptions are not

appropriate for your particular study, then

this can bring into question the output of the

model.

Cost is another big factor in choosing a

model. You may find you need to tailor your

modelling exercise to fit your budget.

You should only do this, however, if you’re

confident that the results you get will be

meaningful and will answer the ‘what if’

question(s) you aim to answer. Also, be sure

to consider the cost of ongoing technical

support. Models are like machines—the

more refined they are, the more maintenance

they generally need.

Choosing the ‘right’ model

10


As a rule of thumb,

it’s usually better

to go with as simple

a model as possible

that adequately fulfills

your needs.

Some models can be developed quickly

and cheaply but the results may not be

good enough to base important

resource management decisions on.

A simple model may be enough to assess

the broad impact of a certain proposal, but

would not usually be sufficient for project

approval or licensing purposes. On the other

hand if a more reliable model is required, it is

not likely to come quickly or cheaply.

There are three main classes of models(described more fully in Middlemis et al. 2001):

A basic model is a simple model suitable forpreliminary assessments (rough calculations)that does not need significant resources todevelop. It is not suitable for complexconditions or detailed resource assessment.Such a model can cost between $2,000 and$8,000 and can take between several daysto a few weeks to build.

An impact assessment model is moderatelycomplex, requiring more information and a

better understanding of the groundwatersystem. It is generally suitable for predictingthe impacts of proposed developments ormanagement policies. Such a model can costbetween $10,000 and $100,000 and requiresa few weeks to several months work.

An aquifer simulator is a complex modelsuitable for predicting responses to changesin hydrological conditions and for developingsustainable resource management policiesfor groundwater systems. This type of modeloften costs more than $50,000 and takesmonths to years to develop. A large budgetand long timeframes are needed for ongoingdevelopment.

Deciding upon the relevant model complexityrequires negotiation with the modeller.Review by an independent expert adviser onthe appropriateness of the design approachcould be a worthwhile investment.

There are also certain external factors thatimpact on the complexity of models availablefor a given situation. These are consideredon page 17.

Types of models

11



the broad impact of your proposal.


the broad impact of your proposal.


Choosing the ‘right’ modeller can be as

important as choosing the ‘right’ model.

When choosing a professional adviser, do you

only concern yourself with the instruments of

their trade or do you also make your decision

on the basis of their experience and

reputation? That said, some ‘experts’ are too

expensive, too far away or have a full schedule.

The same principles apply when choosing a

modeller. You need to consider and assess all

these factors before engaging a modeller,

although distance may not necessarily be a

concern. It may not matter that the modeller

is based in Adelaide studying a groundwater

system in Queensland, as long as you have

the budget for commuting to periodic face-

to-face meetings.

It is important to ensure that the modeller

engaged to do the study has the necessary

skills. The modeller’s performance on previous

studies should be adequately investigated,

including discussions with nominated referees

and other independent contacts.

Whoever you choose, be careful about

becoming locked into using the same modeller

in the future—keep your options open.

Choosing the ‘right’ modeller

12

It is important to ensure

that the modeller

engaged to do the study

has the necessary skills.


Groundwater models need to be well

designed and well constructed so that

they adequately represent the natural

system being modelled. When a model

is developed, it is important that all

those involved understand the role they

need to play in the process in order to

alleviate any potential problems.

There is also a need to understand why the

model is needed, how it will work, the

underlying assumptions and limitations, and

the outcomes expected.

Table 1 outlines the typical roles and

responsibilities of the project manager and

modeller during the development of a

groundwater model to assist catchment

management decision-making.

Models are a team effort

13


Team member Key roles and responsibilities

Project Manager • Define objectives and model purpose

(model purchaser) • Define communication needs and engagement process

• Oversee scoping study

• Define realistic requirements and performance measures

• Outline realistic scenarios for model prediction

• Assist in access to data and information*

• Review and identify information gaps

• Review conceptual model

• Provide information and resources to assist with data problems

• Review outputs

• Determine model ownership and intellectual property rights

• Determine handover and training requirements and

maintenance plans

• Accept final model and report

Modeller(s) • Submit detailed model proposal

(model provider) • Outline the project management structure, milestones and

review plans

• Collect data*

• Carry out literature and technical data review

• Undertake communication activities

• Develop conceptual model, model code selection and model

study plan

• Develop model

• Communicate progress and outcomes

• Undertake internal review and audit

• Write final report on model

* Significant allocation of time and budget likely to be required.

Source: Adapted from: Middlemis et al. (2001), Groundwater flow modelling guideline. Murray-Darling BasinCommission, pp. 5-6

Table 1: Outline of Roles and Responsibilities

A scoping study should be carried

out before engaging a modeller on a

full-scale modelling project. However,

it need not be done by the same

modeller that undertakes the full-

scale project.

The purpose of the scoping study is to

define the project objectives and purpose

of the full-scale modelling project, in light of

the resource management issues you want

to address. Asking the ‘right’ question is

an important step in the scoping study and

it must be made before launching into the

detailed modelling effort. The scoping

study process will allow you to discuss and

agree on the appropriate level of model

complexity.

The scoping study should also clearly define

the information and management constraints

like data availability, budget, timeframe and

intellectual property issues. The result is a

project brief or ‘terms of reference’ to use as

the basis for engaging a modeller directly or

undertaking a public or selected tender

process.

The scoping study

14


The scoping study

process will allow you

to discuss and agree on

the appropriate level of

model complexity.


15


The development of any groundwater model requires four stages—conceptualisation(which includes the scoping study), data collation, calibration and prediction. Table 2 describes the steps involved in each of these four stages.

Model development

Stage Description Tasks

1 Conceptualisation • Define study objective (general and specific) and model This stage commonly complexitycomprises about 20% • Complete initial hydrological and hydrogeological (sometimes up to 40%) studies, based on available informationof the study effort • Prepare conceptual model (see page 16)

• Select appropriate modelling code—the computer program used in the mathematical model

• Prepare detailed model study plan (outline grid, layers, boundaries, timeframes, accuracy targets, resources and information needed)

• Report and review

2 Data collation • Get access to and purchase existing data (availability This stage comprises about and accessibility issues should have been determined 20% of the study effort during scoping study) (sometimes up to 50% • Formalise intellectual property arrangementswhere data collection and/or • Transform or manipulate datatransformation is needed) • Collect additional data, where required

3 Calibration • Construct model by designing grids, setting boundaryThis stage commonly conditions and assigning parameters comprises about 40% • Calibrate model by adjusting parameters until simulationof the study effort results closely match measured data

• Complete model analysis• Report and review

4 Prediction • Run prediction scenariosThis stage commonly • Complete analysis of how sensitive outputs vary withcomprises up to 20% changes in model inputsof the study effort • Report and review, including reliability and performance

measures

Source: Adapted from: Middlemis et al. (2001), Groundwater flow modelling guideline. Murray-Darling BasinCommission, p. 17

Table 2: Summary of model development

The most important step in a modelling

study is the development of a valid

conceptual model. This is done after

definition of the study objectives, model

purpose and model complexity at the

scoping stage.

A conceptual model is a simplified

representation of the key features of the

physical system and its behaviour.

It forms the basis of the mathematical

(computer-based) model by providing

information that can be developed into

a prediction phase. The conceptual model

is subject to some assumptions partly

because there is rarely enough information

to describe the system fully.

From the conceptual model, the

mathematical model is developed

(as described in Table 2).

The conceptual modelUNDERTAKING A SUCCESSFUL STUDY

16

Source: Middlemis et al. (2001), Groundwater flow modelling guideline. Murray-Darling Basin Commission, p. 26

Typical block diagram conceptual model

River inflow

Evapotranspiration

Irrigation areaor wetland

Abstractions

Rainfallrecharge

River

WaterTable

Riveroutflow

Layer 1(superficial deposits)

Layer 2(sandstone)

Layer 3(basement)

Groundwateroutflow

Fault

Groundwaterinflow

17

Before you start making investment

or management decisions based on

the model outputs, you need to be

sure that the results it has produced

are reliable.

Reliability, however, can never be 100%.Limitations and uncertainty exist in anymodelling study, regardless of its complexity,due to constraints such as:

• the availability of critical data• the level of hydrogeological understanding• the detail and robustness of the conceptual

model• the ability of modelling software to represent

real-life processes• mathematical model calibration.

The question of model reliability should beconsidered in some detail at the scoping studystage. Reliability targets should be agreed tobefore construction of the model begins. Thetargets can always be adjusted and refined asthe project develops.

Described below are three standard tests thatcan provide an indication of the reliability of amodel.

The first test compares model estimatesagainst historical measurements. The modelshould be able to accurately predict whatoccurred in a particular system during thepast, such as the peaks and troughs ofstreamflow or groundwater levels over a 10-year period, or the lowering of thegroundwater table caused by long-termpumping.

The second test, known as ‘field validation’, is an important but not always affordable one.Under this test, model assumptions andresults are tested in the field by, for example,drilling bores to check soil properties orwatertable levels.

A ‘sensitivity analysis’ is the third type of test.This test can point to parts of the model wherea small change in some of the inputs orassumptions can make a big difference to theresult. For example, a small change in the rateof tree growth may result in significantly reducedstreamflow. This may cause you to decide toconcentrate on further developing this part ofthe model or improving specific data.

When you are confident that the modeloutput is valid, you can then use it to predictscenarios and answer your ‘what if’questions. If you have built a flexible model,you can upgrade it when more databecomes available.

Irrespective of the confidence you have inthe model, always use the results of themodelling process with due care. Rememberthat models do not produce absoluteanswers; they produce estimates. It is theseestimates that you use to inform yourdecision-making processes.

You can use models as learning tools, toquestion and to refine your understandingand experience of the real world. Models canplay a useful role in examining the complexrelationships between people, land and water,but always keep in mind that it is just asimplified version of the real world based onincomplete knowledge.

Model reliabilityUNDERTAKING A SUCCESSFUL STUDY

It may be worthwhile forming atechnical group to assist with variousaspects of model construction andimplementation. This could includeassisting in the preparation of thescoping study, giving advice on thedesign of the conceptual model,overseeing data collation, reviewingmodel outputs and comparing studyfindings against objectives.

The group needs the appropriate skills toproperly perform these tasks. Some of thespecific skills include:

• local hydrogeological knowledge• expertise in selecting appropriate software

for modelling

• ability to liaise with regulators or agencies to obtain data and resolve data conflicts and uncertainties

• communication.

The group, or the project manager alone, needsthe ability to deliver the modelling study within aset budget and timeframe, support expansionsof the model and manage any communicationactivities.

The group must also agree on the best processfor engaging a modeller. Engaging a modellerfor only the scoping study provides a goodopportunity to observe their work and toestablish a working relationship. On this basis,you may decide to use the same modeller forthe rest of the study or you may decide youneed to look for an alternative.

Overseeing the study

It is recommended that periodic reviewsbe undertaken throughout anygroundwater modelling project. Eachreview provides a check to see if themodel is meeting project objectives.

The scope of the review will depend on thecomplexity of the project and can range frommodel appraisal and compliance using a simplechecklist, to more comprehensive peer reviewsor a complete model audit. Ideally, the modellershould be aware of the evaluation criteria for themodel at the commencement of the study.

An appraisal and peer review usually involves areview of the study report, while an audit

requires an additional in-depth review of theactual model input files, scenario simulationsand outputs.

The technical group (or an independentreviewer) can conduct a model appraisal, whilea peer review or model audit needs to becarried out by an independent experiencedgroundwater modeller.

A post-audit is usually carried out by the originalmodeller, but can also be done by anindependent modeller with access to the modelsoftware and information.

Carrying out regular reviews will add cost to theoverall project. It is important that all parties agreeon who will bear these costs from the outset.

Reviewing the model

18


Models are increasingly being used

to assess the merits of different management,

policy and investment options.

Models are increasingly being used

to assess the merits of different management,

policy and investment options.

Groundwater models can help you todevelop and evaluate options formanaging natural resources that willassist you in making cost-effectiveand more sustainable decisions foryour catchment.

Models are increasingly being used by

catchment communities and resource

managers to assess the merits of different

management, policy and investment

options.

There are many types of groundwater

models available and many factors that need

to be considered to ensure that your

modelling study is successful. It is important

to match the model (and the modeller) with

your specific needs, data availability,

timeframe and budget.

The modelling process is an important one

that requires a clear set of objectives,

teamwork, a robust system of review, and

guidance by appropriately skilled

professionals.

Summary

Source: © Peter Solness/Network Photographers 19

The following definitions provide

a plain-English description of

modelling terms:

aquifer—a formation of rock or soil that isable to carry significant amounts of waterto wells and springs. It must be saturatedby water and allow water to pass throughit (be permeable).

conceptual model—a simplified ‘picture’of how a groundwater system works. It maps key water flow processes,according to the surface and undergroundproperties of the region.

data set—a collection of measurements and descriptions. A data set can createinformation when it is interpreted.

groundwater model—a computer-basedrepresentation of the key features of agroundwater system. It incorporates two keyelements, a conceptual model and amathematical model.

groundwater flow—the movement of waterthrough layers of rock. The groundwatermoves through what is known as the zone of saturation.

hydrogeology—the study of groundwaterand how it is related to the sub-soil and rocklayers and its associated features.

mathematical model—a set of equationsthat describe physical processes of theaquifer(s) being investigated. Usinginformation on climate, geology andlandscape interaction, it allows the modellerto predict the likelihood of future events.

Glossary

Source: Lisa Robins20

Integrated catchment management in the Murray-Darling BasinA process through which people can develop a vision, agree on shared values and behaviours, make informeddecisions and act together to manage the natural resources of their catchment: their decisions on the use of land,water and other environmental resources are made by considering the effect of that use on all those resourcesand on all people within the catchment.

Our valuesWe agree to work together, and ensure that our behaviour reflects that following values.

Courage

• We will take a visionary approach, provideleadership and be prepared to make difficultdecisions.

Inclusiveness

• We will build relationships based on trust andsharing, considering the needs of futuregenerations, and working together in a truepartnership.

• We will engage all partners, including Indigenouscommunities, and ensure that partners have thecapacity to be fully engaged.

Commitment

• We will act with passion and decisiveness, takingthe long-term view and aiming for stability indecision-making.

• We will take a Basin perspective and a non-partisan approach to Basin management.

Respect and honesty

• We will respect different views, respect each otherand acknowledge the reality of each other’ssituation.

• We will act with integrity, openness and honesty,be fair and credible and share knowledge andinformation.

• We will use resources equitably and respect theenvironment.

Flexibility

• We will accept reform where it is needed, bewilling to change, and continuously improve ouractions through a learning approach.

Practicability

• We will choose practicable, long-term outcomesand select viable solutions to achieve theseoutcomes.

Mutual obligation

• We will share responsibility and accountability, andact responsibly, with fairness and justice.

• We will support each other through the necessarychange.

Our principlesWe agree, in a spirit of partnership, to use the followingprinciples to guide our actions.

Integration

• We will manage catchments holistically; that is,decisions on the use of land, water and otherenvironmental resources are made by consideringthe effect of that use on all those resources andon all people within the catchment.

Accountability

• We will assign responsibilities and accountabilities.

• We will manage resources wisely, beingaccountable and reporting to our partners.

Transparency

• We will clarify the outcomes sought.

• We will be open about how to achieve outcomesand what is expected from each partner.

Effectiveness

• We will act to achieve agreed outcomes.

• We will learn from our successes and failures andcontinuously improve our actions.

Efficiency

• We will maximise the benefits and minimise thecost of actions.

Full accounting

• We will take account of the full range of costs andbenefits, including economic, environmental,social and off-site costs and benefits.

Informed decision-making

• We will make decisions at the most appropriatescale.

• We will make decisions on the best availableinformation, and continuously improveknowledge.

• We will support the involvement of Indigenouspeople in decision-making, understanding thevalue of this involvement and respecting the livingknowledge of Indigenous people.

Learning approach

• We will learn from our failures and successes.

• We will learn from each other.

This compact handbook is designed

specifically for catchment communities

and natural resource managers as a

guide to understanding and developing

groundwater models.

It explains that:

• Groundwater is an important resource, however, many systems are

out of balance and causing land and water degradation

• Catchment investments in land and water management can be

prioritised using groundwater modelling

• Groundwater models are an important tool in predicting the

consequences of our actions in a catchment

• Communities will benefit most from a groundwater model when:

– project objectives are defined through a thorough scoping study

– a skilled modelling team with local knowledge of the groundwater

flow system(s) undertakes the study

– communication and review of the modelling activities are carried

out throughout the study.

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