2015 design project 2 brief

C&ENVENG 4109 / 7109 – Environmental Engineering Design IVB

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The University of Adelaide

School of Civil, Environmental and

Mining Engineering

Weeks 5 - 12, Session 2, 2014

Project 2a and 2b: Securing Adelaide’s future water: updated design for Mt

Bold reservoir

Project Leaders: Dr Seth Westra, Mr Sam Culley

E-mail: [email protected], [email protected]

1. INTRODUCTION Mount Bold reservoir is South Australia’s largest, and at nearly 80 years of age it is approaching the

end of its design life. A lot has changed since its construction in 1938, and projections of a decline

in catchment runoff due to climate change, combined with population growth, will mean that it will

become increasingly challenging to supply water for Adelaide throughout the 21st century.

In addition to the twin challenges of climate change and population growth, negotiations with the

Commonwealth government regarding use of flows from the Murray River to supplement

Adelaide’s natural catchment flows have broken down, which means that Murray River pipeline

flows will cease as of 1 January 20181. A preliminary analysis has shown that there are only two

options remaining: maximising the water supply from Adelaide’s natural catchments, and

desalination2.

To this end, earlier today your manager received a letter from the South Australian Hydrology

Department (SAHD3) requesting (as a matter of urgency) that your company undertake a

hydrological investigation that will inform an upgrade of Mount Bold reservoir. The objective of the

upgrade is to support Adelaide’s water supply needs throughout the 21st century at the least possible

cost. Your company is receiving significant pressure from SAHD to maximise the natural catchment

extractions from the Onkaparinga and thus minimise the use of the more expensive desalination

plant, however you must also balance the environmental water requirements and flood risks

downstream of the dam.

This investigation will involve extensive hydrological modelling, and will require two separate

reports: an INITIAL report that should focus on the hydrological model for the Onkaparinga

catchment, and a FINAL report that should focus on the recommended reservoir design. Note that

detailed costings are NOT required – you can assume that desalinated water is much more

expensive than water from the reservoir, and therefore the lowest cost solution means maximising

supply from the reservoir subject to the environmental and flood protection constraints.

1 This is a not a true scenario, although during the Millennium drought there was genuine concern about the security of

Murray River as a source of water for Adelaide, which was one of the reasons for the state government’s decision to construct a desalination plant. 2 In reality there are several other options available, including groundwater extraction and aquifer recharge, rainwater

tanks, and several other smaller reservoirs scattered throughout the Mt Lofty ranges, but I’m keeping the system simple for the purposes of this assignment. 3 This is a fictional government department. The actual department with responsibility for Adelaide’s water security is

the Department of Environment, Water and Natural Resources.

mailto:[email protected]

mailto:[email protected]


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2. BACKGROUND TO THE ONKAPARINGA CATCHMENT

The Onkaparinga catchment (Figure 1) is situated to the south-east of Adelaide in the southern

portions of the Mount Lofty Ranges, and exits to the ocean near Old Noarlunga. It is a significant

source of municipal water for metropolitan Adelaide, and also provides water to farm dams and the

environment.

The catchment has a total area of 553 km2, with a significant elevation gradient ranging from low-

lying coastal plains near the mouth of Old Noarlunga to elevations of 700 m in the upper reaches

within the Mount Lofty Ranges. Partly due to these orographic features, the catchment has a

substantial rainfall gradient, with a median catchment-average annual rainfall of about 780 mm but

ranging from approximately 500 mm along the coast to 1100 mm at higher elevations. The areal

potential evapotranspiration calculated using Morton’s APET formulation [McMahon et al., 2013]

is approximately 1300 mm per year, while the pan evaporation recorded at Mt Bold reservoir is

1560 mm per year [Teoh, 2002].

Mount Bold reservoir has been operational since 1938, and this reservoir diverts water to supply

Happy Valley reservoir. Catchment inflows have up until now been supplemented with water

pumped from the Murray River, which enters the system near Hahndorf. Houlgrave Weir is situated

just upstream of Mount Bold reservoir, and has long and high-quality records of historical

streamflow. Flows past this weir are mostly derived from the upstream catchment during the winter

months, and from the Murray River during the summer months. In the upper reaches of the

catchment there are a number of towns, including Aldgate, Bridgewater, Balhannah, Lobethal,

Hahndorf, Stirling, Summertown, Uraidla and Woodside.

A study by Teoh [2002] gives a detailed account of the catchment hydrology, focussing on the role

of farm dams. A more recent study by Heneker and Cresswell [2010] covers the predicted impacts

of climate change on the Mount Lofty Ranges. The purpose of the analysis was to determine likely

changes to water storage reservoir inflows. Their assessment was based on a statistical downscaling

approach (the non-homogenous Markov model; NHMM) in conjunction with existing hydrological

models. They used one simulation from a single GCM for each of two emission scenarios, A2 and

B2 [IPCC, 2000], and focused on the time slice 2035-2065. They concluded that climate change

represents a significant risk to Adelaide’s water supply and that changing weather patterns could

potentially reduce annual rainfall by 13%, translating to a potential reduction in annual runoff from

the Mount Lofty Ranges water supply catchments of more than 30%. The largest changes are

expected for the autumn and early winter months, with projected rainfall reduced by as much as

25% during this period. Changes in evaporation rates were not modelled as part of their

downscaling process.

The Onkaparinga catchment is shown in Figure 1. The portion of the catchment of interest for this

study – namely the portion that supplies water to Adelaide – is located upstream of the Happy

Valley reservoir diversion, and is largely represented by three sub-catchments: Scott Creek,

Houlgrave Weir and Echunga Creek. These three catchments have high-quality streamflow gauges

at each of the catchment outlets, which make them suitable for hydrological analysis.


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Figure 1: The Onkaparinga catchment


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3. PROJECT OBJECTIVES AND DELIVERY

The aim of this study is to develop a new multi-purpose reservoir that will replace the current

Mount Bold reservoir, and which should satisfy the following requirements:

Municipal water supply for Adelaide and parts of the Mount Lofty Ranges;

Environmental water requirements in the lower reaches below Mt Bold reservoir; and

Capacity to detain peak flows up to the 10% Annual Exceedance Probability (AEP) event.

You should assume that the new reservoir will be situated at the same location as the current Mount

Bold reservoir, but otherwise you are not constrained by the existing reservoir design. It is expected

that construction will begin in early 2016 and will need to be completed by 1 January 2019.

To support the updated reservoir design, the following hydrological analysis will be required:

A comprehensive investigation of the quality and suitability of the historical data (rainfall,

catchment potential evapotranspiration, lake-surface actual evaporation, and streamflow)

that will underpin the hydrological investigation;

Initial assessment of the catchment using the Budyko framework and runoff coefficients

One or more calibrated and validated rainfall-runoff models, using the Source Catchments

software. The model(s) will support the investigation into alternative reservoir design

options;

Assessment of historical flows in the Onkaparinga catchment, including an assessment of

“natural catchment flows”. This assessment should consider both the aggregate flows into

Mount Bold reservoir, as well as the flows immediately downstream of the Clarendon Weir

offtake (the location at which water is extracted and piped to Happy Valley reservoir and

ultimately to Adelaide). These time series will inform the development of environmental

flow rules;

An assessment of future flows based on alternative climate change scenarios, projected up to

the end of the 21st century;

An estimation of municipal water demand for Adelaide and parts of the Mount Lofty Ranges

based on current and future population projections;

Flood modelling to set the spillway level, with flood storage in the reservoir to hold the 10%

AEP flood event;

An exploration of implications of alternative operating rules on water supply, environmental

flows and peak flows; and

An exploration of the modelling uncertainties using stochastic generation techniques and

investigating alternative population projections and climate change scenarios, and the

implications of those uncertainties on the reservoir design.

SAHD recognises that the natural water supply from the Onkaparinga catchment will be

insufficient to meet Adelaide’s future water supply. Nevertheless, SAHD’s economic analysis

has shown that the natural water supply from the Onkaparinga catchment is currently the cheapest

available water source, and therefore wishes to maximise the water supply from this catchment.

Your report is to provide advice to SAHD in relation to the amount of water that can be sustainably

supplied from the Onkaparinga to support Adelaide’s water supply.

You are to use your results to describe:


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(a) The amount of water that can be supplied to Adelaide (both an annual volume and expressed

as a percentage) in a typical year, as well as a quantitative description of the year-to-year

variability (including, but not limited to, the 10 and 90% quantile of annual flows). This will

need to be provided for both current and future climate projections, accounting for current

and future water demand projections;

(b) The maximum capacity of the desalination plant that will be needed to supplement the flows

from the reservoir. Note that significant capital costs are associated with constructing a

desalination plant, and therefore you are to comment on the ability of the reservoir to

‘smooth out’ variations in natural catchment flows (for example because of South

Australia’s strong seasonal cycle).

(c) Reservoir dimensions, including: dead storage level, active storage level (potentially divided

between water supply and flood detention storage), the reservoir outlet configuration and the

spillway level;

(d) A description of the environmental water to be provided by the reservoir relative to “natural”

catchment flows;

(e) A set of reservoir operation rules to ensure that the reservoir maximises municipal water,

while maintaining sufficient environmental flow and addressing downstream flow risk.

Figures, maps and sketches to illustrate the report should be regarded as essential and reports that

are not appropriately illustrated will be penalised.

You will have access to numerous reports and investigations of the Onkaparinga catchment.

Additional notes on relevant methods, and software manuals, are also available on MyUni. You

will also be required to search the library and the scientific literature to supplement this

material. You are not expected to become an expert but you are expected to assemble material to

adequately define the issues, tasks, priorities and scheduling of studies that would need to be

considered in during a detailed study.

Where to go for help

This assignment is designed to emulate the ‘real-world’ design environment, with challenges

including

An ‘open-ended’ design problem with multiple possible solutions;

Multiple potentially conflicting sources of information, including alternative datasets

that might contain measurement errors or other issues; and

Multiple alternative methods that can be used for each of the calculations.

Lectures will be designed to provide a general overview of the major issues and topics, and

some suggestions on possible methods to develop solutions. The tutorials will focus on

providing assistance on specific software needs, including eWater’s Source Catchments

which will be the main model for you to use. You are also encouraged to attend the design

sessions to obtain feedback and help along the way.

You are strongly encouraged to use the discussion board for any issues, and I will monitor

this and respond to issues as appropriate. Finally, I will make an hour available each week as

a consulting hour, with the time to be advised on MyUni.


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4. REPORT REQUIREMENTS Two separate reports are to be produced for this assignment: an INITIAL report (worth 20%),

which should focus on setting up the hydrological model, and a FINAL report (worth 20%), which

should focus on the recommended design for a multi-purpose reservoir that will replace the existing

Mount Bold reservoir. The scope of the two reports is discussed further below. Please refer to

MyUni for due dates for each of the reports.

4.1 Initial report

An INITIAL report should focus on the following areas:

A description of the approach used to generate catchment-average rainfall and potential

evapotranspiration data as an input to the hydrological model, streamflow data for model

calibration and validation, and actual evapotranspiration estimates from the reservoir

surface. This should include a thorough assessment of the quality and suitability of the data,

as well as a description of the catchment using the runoff coefficient and the Budyko

framework. All data is to be expressed as a rate of mm depth per year. Note, there will not

be a reservoir when simulating the “natural” flow conditions, but the lake evaporation rate

still needs to be provided as it will form an input to the final report;

One or several calibrated and validated daily hydrological model(s), including a justification

for the choice of model(s) to be used in the final report, a discussion of the approach used to

estimate parameter values (e.g. choice of objective function and optimisation routine) and a

summary of the calibrated/validated model performance; and

A description of the “natural” or “pre-reservoir” flow conditions, including plots of annual

average runoff, monthly and/or seasonal average runoff, and the daily flow-duration curve

including a summary of various quantiles (e.g. 10, 50, 95 and 99 % quantiles). This

description should include the aggregate flows into Mount Bold reservoir, as well as the

flows immediately downstream of Clarendon Weir offtake.

The INITIAL report is not to exceed 20 pages in length including figures (appendices may be

additional to the main report, but should be no more than 15 pages on their own). Note that the

executive summary and the table of contents are additional to the 20 page limit.

4.2 Final report

A FINAL report should be produced to focus on:

Estimated demand for Adelaide city at various future time horizons (based on reservoir

design life considerations);

Reservoir inflow scenarios under historical and future climate scenarios, and the elasticity

of the catchment determined from the Budyko model;

The amount of water that can be supplied to Adelaide (both an annual volume and

expressed as a percentage) in a typical year, as well as a quantitative description of the year-

to-year variability (including, but not limited to, the 10 and 90% quantile of annual flows).

This will need to be provided for both current and future climate projections, accounting for

current and future water demand projections;


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The maximum capacity of the desalination plant that will be needed to supplement the

flows from the reservoir. Note that there are significant capital costs associated with

constructing a desalination plant, and therefore you are to comment on the ability of the

reservoir to ‘smooth out’ variations in natural catchment flows;

Reservoir dimensions, including: dead storage level, active storage level (potentially

divided between water supply and flood detention storage), the reservoir outlet capacity

and the spillway level;

A description of the environmental water to be provided by the reservoir relative to

“natural” catchment flows;

A set of reservoir operation rules to ensure that the reservoir maximises municipal water,

maintains sufficient environmental flow and addresses downstream flood risk; and

A brief outline of any future investigations that need to be performed for a detailed water

supply design.

The FINAL report is not to exceed 25 pages in length including figures (appendices may be

additional to the main report, but should be no more than 20 pages on their own). Note that the

executive summary and the table of contents are additional to the 25 page limit.


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5. REFERENCES

Heneker, T. M., and D. Cresswell (2010), Potential Impact on Water Resource Availability in the

Mount Lofty Ranges due to Climate ChangeRep., Government of South Australia, through

Department for Water, Adelaide.

IPCC (2000), Special Report on Emission Scenarios Rep., WMO and UNEP.

McMahon, T. A., M. C. Peel, L. Lowe, R. Srikanthan, and T. R. McVicar (2013), Estimating actual,

potential, reference crop and pan evaporation using standard meteorological data: a pragmatic

synthesis, Hydrological Earth Systems Science, 17, 1331-1363.

Teoh, K. S. (2002), Estimating the Impact of Current Farm Dams Development on the Surface

Water Resources of the Onkaparinga River CatchmentRep., Department of Water, Land and

Biodiversity Conservation.

2015 design project 2 brief

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