Whole of Catchment Urban Stormwater Retrofits · • Methodology applied by BMT WBM have a number of distinct elements • The ultimate goal is to include sufficient retrofit (if

Whole of Catchment Urban Stormwater Retrofits

Various QLD and NSW Case Studies

CanberraMay 2012

Damion Cavanagh – Associate BMT WBM Bangalow, Northern NSW

CanberraMay 2012

Context

What are we talking about here?

• Water quality degradation of urban streams, unable to meet Water Quality Objectives

• Diffuse urban loads contributor to water quality problems

• Need a structured method of assessing extent of problem caused by diffuse loads and benefit / cost obtained by retrofit with quality control devices

• MUSIC very useful component tool in these assessments

• Enables relatively simple determination of load reduction and cost benefit

• Cost benefit understanding enables prioritisation

What does it give you?

Why is this information useful?

• There are a number of uses of this information

• Useful for a Council, Utility or NRM body to understand likely full cost of meeting WQOs through stormwater retrofit or planning controls, if possible at all.

• Provides plan for action and costs

• Identification of costs allows appropriate funding models to be considered, i.e. can Council’s do it alone, can costs be shared, are other options preferable to achieve outcomes.

• For instance, addressing point source inputs (e.g. STP) may be less costly. Not always an option though.

Is it common to do this?

Committed to by a number of Councils...

• In SEQ largely driven by Healthy Waterways Strategy –provides alignment of local, state and national directives

• Some Council’s are committing to targeted retrofit of existing urban areas to achieve 100% WSUD performance standards (and hence WQOs), but over a longer timeframe, i.e. 2026.

• In NSW approaches appear to vary by regional drivers, i.e. need for high water quality to support local industries, e.g. water quality, etc.

What is the method?

Its about the receiving waters ultimately:

• Methodology applied by BMT WBM have a number of distinct elements

• The ultimate goal is to include sufficient retrofit (if possible) to reduce loads and achieve WQOs

• Catchment modelling covers a defined period with good data coverage

• Existing case loads integrated into receiving water quality model

• Water quality model calibrated to available data

• Provides some confidence about catchment model exports

Example Calibration

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TN Tracer - Site 3 Modelled

TN - Site 2903 EHMP Recorded

TN - Council Site 5A Recorded

C:\Projects\B18298_Currumbin_Ck\Modelling\TUFLOW\Calibration_Results\WQ_cal_run36_PAR.xlsx

What is the method?

Continued:

• Catchment models updated with retrofit scenarios and rerun

• New catchment exports integrated into receiving water model and rerun

• Process continued until objectives met

Options:

• Various scenarios to assess particular treatment styles

• Can be run at different times (i.e. historic or future case) provided that sufficient information available, i.e. landusedatasets

Application of MUSIC

MUSIC fits this space...

• When considering whole of catchment urban retrofit study, MUSIC has proven to be a very useful tool.

• Flexible in its ability to allow the user to create multiple models and join them later. Avoids excessively large models in dense urban areas, without loss of accuracy

• There is sufficient data to allow models to be created to accurately reflect the wide variety of whole of catchment landuses, which can be diverse.

Application of MUSIC

MUSIC fits this space...

• Models can build in existing features of catchment, e.g. existing treatment systems, hydraulic controls. There may be many different types of existing systems!

• Can quickly supply a variety of data for reporting purposes, including identification of pollution hotspots

• MUSIC was used in the costing of the various retrofit controls being considered.

• In our application, it was also used to supply a time-series of loads to inform receiving water quality models

Hotspots

What have been the outcomes?

What did it tell us:

• Various modelling scenarios were devised and tested, some scenarios formulated considered the likely effectiveness of planning controls

• For the catchments previously considered which have been >20km2 and had greater than 25-60% urbanisation, it has not been possible to achieve all WQOs through retrofit.

• However, significant reductions in pollutant loads could be achieved.

• Achievement of WQOs would necessitate, other more drastic actions, including resumption of private lands to site treatment devices!!


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TSS Modelled 2031 Unmitigated

TSS Modelled 2031 Scenario 1

TSS Modelled 2031 Scenario 2

SMD Mid‐EstuaryWQO for TSS <13 mg/LTurbidity <7 NTU

Existing HEV Turbidity WQO < 5 NTU



• The process has raised questions as to the suitability of existing WQOs as with even high levels of retrofit, increased planning controls, the objectives still weren’t achievable.

• In the siting of potential devices, a reverse engineering philosophy is required, as the approach requires the existing design approach to be dissected, and rejoined with stormwater controls integrated

• There are a number of practical limitations in this, e.g. space, community acceptance, services, it is useful to Council (or client) in this process to ensure that approaches to siting and selection of options is reasonable



• There are often a lot more stormwater controls present in a catchment than others may be aware of… we once identified about 80 in detailed site inspections, but were only informed of 6!

• In terms of cost, the cost of retrofit will obviously vary from catchment to catchment and depend heavily on the load reductions required. Capital costs of the order of

XXXX/km2 have been identified previously

• These studies take a long time, they are data and modelling intensive, and require systematic approaches to effectively reach the desire end point



• The process of prioritization can be subjective, a clear and unbiased approach is required.

• We have found a suitable method is to assess treatment trains (not individual devices) for cost and performance

• Treatment trains can then be considered on a cost per unit of performance, i.e. $/kg pollutant removed

Whole of Catchment Urban Stormwater Retrofits · • Methodology applied by BMT WBM have a number of distinct elements • The ultimate goal is to include sufficient retrofit (if

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