Introduction

These s3qm Modelling Guidelines have been developed to assist proponents preparing s3qm models to predict the impact of proposed land use change on stormwater quality through urban and rural developments within New South Wales.

To manage the impacts of land use change on stormwater quality, a number of management techniques can be implemented, including gross pollutant traps, biofiltration systems and rainwater tanks. The s3qm model has been designed as a simple tool to estimate stormwater pollution generation and simulate the performance of stormwater management techniques as part of a treatment train. By simulating the performance of stormwater quality improvement measures, s3qm provides information on whether a proposed system conceptually would achieve water quality targets and, in the Sydney Catchment Authority (SCA) catchment whether a ‘”Neutral or Beneficial Effect on Water Quality” (NorBE) criteria would be satisfied as require by State Environmental Planning Policy (Sydney Drinking Water Catchment) 2011.

This document aims to show practitioners how to set up an s3qm model, considering the site layout, the climatic region in which it lies and the configuration of treatment measures. It is not intended as a detailed design tool and it also is not a substitute for knowledge and experience in catchment modelling and the application of Water Sensitive Design (WSD) principles.

When to Use s3qm

s3qm shall is intended to be used for assessing impacts to stormwater quality from a proposed development where the development size does not require the use of MUSIC (Model for Urban Stormwater Improvement Conceptualisation – eWater Ltd). That is, it should be used where:

The total impervious area of the proposed development,including future dwellings and associated works is less than 2500m²; and/or
The proposed subdivision is less than 4 lots; and/or
The impervious area is <70% of the total site area; and/or
For all commercial and industrial subdivision development applications less than 2500m² and/or
For any development where the total disturbed area is less than 2500m².

Above these thresholds MUSIC should be used for Development Applications (DAs) unless specific requirements by individual Councils have been identified (such as within a Development Control Plan).

Setting up an s3qm model

There are three broad options for setting up an s3qm model. The following section outlines these options and provides a summary of the steps required to set up and run the model.

The three options which the user can choose from are summarised below:

NorBE Design - Neutral or Beneficial Effect on Water Quality. This option automatically sets up s3qm to test the NorBE requirement. This has been set so that modelled water quality shows an improvement of 10% over the existing case for total suspended solids, total phosphorus and total nitrogen. This 10% improvement figure has been adopted to account for uncertainty in model predictions and ensure NorBE is satisfied given this uncertainty.

TTE Design – Treatment Train Effectiveness. This option allows the user to specify the water quality objectives (WQO) or targets to be met. The results are based on whether the proposed treatment train meets these WQO’s.

TTE Deemed to Comply (Solver). This option allows the user to specify the WQO’s. The s3qm will then determine the best treatment train solution to meet the set WQO’s. Note that the solver will only work for the assessment of compliance against Treatment Train Effectiveness, not NorBE.

The figure below outlines the information required depending on the Conceptual Design mode chosen. Further details on each of the steps are highlighted in the steps.

Using s3qm

Open s3qm at http://www.s3qm.com.au. If you are a new user you will first need to register your details. Once you have received your confirmation details via email, you are ready to begin.

Click on Create a New Project and the following user interface appears.

Main Site Details

General Site Information

Enter the project name, project number, council area, site address, lot and DP number and any comments.

Climate Region

Choose the Climate Region for the site location. s3qm contains climate data for 15 regions. For developments in the SCA Drinking Water Catchments refer to SCA Climate Zones map below, while for regions outside the Drinking Water Catchment, consult the table below. When a development site appears to be on the boundary of two zones it is important to analyse closely to determine where the site drains

Climate Regions Outside of the Sydney Drinking Water Catchment

Region	s3qm Model Rainfall Region
Northern Coastal NSW	Coffs Harbour
Central Coast NSW	Taree
Central and Eastern Sydney	Sydney
South Coast NSW	Moruya
Western NSW	Wellington
Western Sydney	Penrith

SCA Climate Zones

Soil Type

There are four options to choose from:

Sandy Loam
Sandy Clay
Sand
Clay

These options are used to determine the infiltration rates of an infiltration treatment device, if used.

Water Quality Assessment Type

There are two options available:

NorBE - Neutral or Beneficial Effect
TTE – Treatment Train Effectiveness
These are summarised above in Setting Up an s3qm Model.

Design Mode

There are two options available:

Design – The user determines the best treatment train solution to meet either NorBE or the WQO’s set.
Solve – The s3qm determines the best treatment train solution to meet the WQO’s set. Note that the solver will only work for the assessment of compliance against Treatment Train Effectiveness, not NorBE.

Total Area (m²)

Enter the total area. This value should not exceed 2500m².

When defining the catchment, it is important to understand the site. This can only be done properly through a site visit and reviewing areas that may flow to particular drainage points or may contain single land uses. A maximum of two sub-catchments can be used for the s3qm model to model an area that may have two outlets from the site.

To sort out whether the site being modelled will need one or two catchments, review a contour or drainage map to see if the water will flow to one downstream treatment measure, or if parts of the catchment will need to be treated by a second, independent treatment measure. The latter case will need two catchments, whereas the former one can be modelled with one.

Once all your data has been entered click on the Save button to move to the next page.

Treatment Train Effectiveness

If the TTE is chosen as the Water Quality Assessment Type, then the target Treatment Train Effectiveness user interface will appear (refer to the figure below).

Enter the target treatment train effectiveness values for Total Suspended Solids, Total Phosphorus, Total Nitrogen and Gross Pollutants. These values are the percent reductions of pollutant loads of the treated development when compared to the same development without any treatments. These objectives are usually specified by the local government agency in the area being modelled.

Existing and Developed Catchment Details

The Existing and Developed section is used for entering the details of catchment land uses and stormwater treatment devices. The Design Mode selected within the Main Site Details will determine what information will be required.

In entering information about the site, the user needs to identify which land use represents the area to be assessed. In the majority of cases, a future development can be represented by Urban, but a catchment may also contain upstream areas of other land uses such as agriculture and forest and these are consistent with the default land uses in MUSIC. The following table shows which land use to use for different areas.

Translation of Land Use/Zoning for s3qm Input

Land use	Use Land Use Tab for
Roofs, driveways, paving, concrete slabs or other hardstand areas	Urban
Urban residential, commercial or industrial	Urban
Rural Residential	Urban
Educational, religious, recreational or medical	Urban
Urban park or residential landscaped gardens	Urban (note that Other Impervious area should be adjusted accordingly)
A vacant lot, cleared grassland, pasture, whether fallow or used for grazing	Agriculture
Crop land and other agricultural land, including intensive livestock such as dairies	Agriculture
Natural or artificial bushland, woodland and forest including pine forest (with or without understory)	Forest
Natural regrowth areas or overgrown gardens	Forest

The land use designations above may not cover every possible combination or land use type, however the user will sometimes have to make a judgement call on the one that best represents the existing or future cases best. Typically for an urban development, the existing land use is urban with no impervious area, whereas the future land use will also be urban but with roof areas and other areas of impervious surfaces.

Urban

Urban area (m²) : This is the total urban area within the catchment.

Roof area (m²) : Sum of the entire roof area for the sub-catchment.

Other impervious area (m²) : this includes roads, riveways and other paved surfaces that is directly connected to the drainage system (i.e. Directly Connected Impervious Area or DCIA).

Note that any area that is not identified as Roof area or Other impervious is assumed to be pervious.

The urban land use should be used where there is an existing or has been a dwelling or other development on the site. It includes the provision for rainwater tank and reuse if that was part of the existing development. In most circumstances an existing development is unlikely to have had any treatment of roof runoff, tank overflow or DCIA + Pervious Area. DCIA represents directly connected impervious area which means any runoff from this impervious area is directly connected to the drainage system. Further information can be found in the user guide.

Rainwater Tanks

Rainwater tanks are not specifically detailed under Treatment Train; however, the reduction of flow and pollutants through the use of rainwater is included in all calculations to determine whether the NorBE test or water quality objectives are met.

Rainwater tanks shall be defined considering the physical constraints of the roof drainage system. Where a tank is located above ground and services a single level building in an urban setting it is likely that gravity drainage of the entire roof area to the tank would be impractical. Where a tank is underground, draining of the entire roof area to the tank may be feasible.

In the rural setting, it is common for the entire roof area to drain to rainwater tanks positioned above ground. The settings within the Rainwater Tank section determine:

How much water is directed to and stored by the rainwater tank through the:

Roof Area – total area within that particular land use in the catchment.
Roof Area to Tank (% Roof Area) – estimate of the % of roof area draining to the tank.
Average Tank Volume (kL per Dwelling) – total tank volume within area divided by no. of dwellings.
No. Dwellings (Total) – Set the total number of habitable dwellings being assessed.

How much water is used and therefore the availability of tank storage through:

Avg. No. Bedrooms – for multiple dwellings, use the average number of bedrooms across all dwellings
Tank Water Use – There are several combinations available for using any harvested water from the tank, either for toilet flushing, toilet and laundry use, toilet, laundry and hot water, and finally, all internal uses.
Land Use for External Watering – This only sets the rate of external watering, so if the area is residential, use the urban land use, for commercial or industrial, use the commercial/industrial selection, and finally, for rural residential, select the rural residential option.

Note that the tank volume is in kilolitres, i.e. 10,000 litres is equal to 10kL.

Receiving Treatment

There are three options for which components of the runoff are directed to the stormwater quality Treatment options. These are Roof Runoff, Tank Overflow, DCIA + Pervious Area (the area of the site identified as “Other Impervious” and any remaining pervious area). Any combination of these three options can be addressed through s3qm.

Agriculture

The information required to input is much less than the urban area as it should only be used for a vacant lot or grassed development site where no dwelling, shed or other development exists or has been on the site, or which has been used for agricultural activity.

Sites containing concrete slabs, hardstand areas or driveways should be modelled as Urban

Forest

Localised Area – input the area of forest (noting the appropriate land use categories outlined in the table under Main Site Details in the user guide).

Treat Runoff – select this if the runoff from the Forest area is to be directed to the Stormwater Quality Treatment.

This should be used for contiguous forest or woodland including regrowth, which should include understory or litter, but should not be applied to isolated trees or clumps of trees. The minimum area of Forest represented should not be less than 100m².

Treatment Train

In managing stormwater quality, water sensitive design measures are best utilised in series as part of a treatment train. The treatment train approach ensures that measures selected in the correct sequence operate most effectively in terms of hydraulic and pollutant removal capabilities. s3qm will not allow incorrect sequencing of treatment measures.

The figure below shows the options available for stormwater treatment within s3qm. It is important to note that the diagram highlights the order in which the treatment measures can be placed, however, it does not specify which is the first treatment that needs to be selected. For example, the first treatment could be selected from the third box, however, this then precludes the use of any treatment measures from the first two boxes as the second form of treatment in the 'treatment train'.

* Note that runoff from a Green Roof cannot be directed to a Buffer Strip.

For further details on the inputs refer to the MUSIC Modelling Guidelines appropriate for your area. For proprietary treatment systems such as Gross Pollutant Traps, Cartridge Media Systems and similar, the treatment efficiencies used must have come from independently verified sources.

Treatment Measures

Below Ground Litter Trap – commonly known as a gross pollutant traps or GPT are usually in-line devices designed to remove litter, organic debris and medium to course sediment from stormwater runoff that may overload other treatment measures. GPTs are highly variable in their design and may range from simple mesh pit inserts to large sophisticated structures employing cyclonic deflection to trap the litter and gross pollutants. The more sophisticated GPTs are generally not utilised at the lot scale. Some GPTs incorporate proprietary filtration devices are more effective at removing finer sediments and nutrients such as phosphorus and nitrogen – these are considered under Cartridge Media Systems.

Biofiltration – often called a raingarden or bioretention system, is specifically designed to capture and treat stormwater runoff from roofs and hard surfaces such as driveways, patios and paved areas. Raingardens utilize a sandy loam media planted with deep-rooted moisture-tolerant plants to physically and biologically filter sediments and nutrients such as nitrogen and phosphorus from stormwater that would otherwise end up in streams. Because filtration through the filter media is a slower process than the generation of runoff, raingardens incorporate an above ground detention storage using bunds or walls to temporary hold the stormwater while it is being filtered through the media. Filtered water is collected through drainage pipes at the base of the filter media and discharged to the stormwater system. The depth of this temporary storage, called extended detention depth, and the thickness of the filter media layer determines the effectiveness of a raingarden in treating stormwater. Raingardens, in conjunction with rainwater tanks and reuse are most commonly used for dwellings.

Buffer Strips - are comparatively level grassed or vegetated areas constructed to filter sheet-flow* runoff from impervious areas. They are effective only immediately downslope of an impervious area and only remove coarser sediment. They are generally employed in conjunction with other stormwater treatment measures. (*Sheet flow is a thin, continuous flow of stormwater over a relatively level surface where flow has not been concentrated into a channel.)

Cartridge Media Systems or Media Filtration Systems - proprietary stormwater filtration devices that can be very effective in removing finer sediment and nutrients provided they are regularly serviced. The filter media, generally in the form of cartridges, incorporates zeolite, perlite and other materials, and sometimes includes membranes. A GPT is usually installed before a cartridge system to remove coarser material. Claimed removal figures for total suspended solids, total phosphorus and total nitrogen for such devices generally reflect optimal conditions, and advice should be sought on acceptable removal values. Cartridge systems are generally not used for individual dwellings.

Green Roofs - building roofs that are covered with vegetation usually growing in a lightweight growth media, and which includes a root barrier, filter and drainage layers, and is underlain by a waterproof membrane. The benefits of a green roof include the trapping and treatment of rainwater, roof insulation, a wildlife habitat, lower local air temperatures, and mitigation of the heat island effect in urban areas.

Infiltration - treats stormwater by infiltrating it into the surrounding soil, and as such the performance of this measure is highly dependent on soil characteristics, with the infiltration rate determined from the soil type under Main Site Details. Deep permeable soils are generally suitable whereas shallow or clayey soils are unsuitable. Additionally soil characteristics such as high acidity, salinity, sodicity or acid-sulphate potential may also make infiltration unsuitable. Infiltration systems should be sited away from structures such as dwellings or roads because of the potential for adverse impacts.

Porous Pavement or Permeable Pavers - allow stormwater runoff to drain through the pavement material or through designed openings between pavers and infiltrate to and through the underlying base-course. Particulate pollutants are filtered out by the sand and other media of the base-course, with the depth of the base-course influencing the effectiveness of the pollutant removal efficiency. The filtered stormwater is typically collected by a subsoil drain and discharged to the stormwater collection system. Porous pavement or permeable pavers are ideally suited to domestic driveways and patio areas.

Sand Filters - in-line systems that work in a similar way to biofitration systems but without the vegetation, and as such are often installed underground. Filtration through the sand media can be slower than stormwater inflow, and a detention storage is invariably incorporated into the sand filter to temporary detain the stormwater while filtration takes place. The filtered stormwater is discharged to the stormwater system via drainage pipes at the base of the sand filter. A gross pollutant trap is typically installed before the sand filter, so as to pre-treat stormwater and prolong the life of the filter.

Swales or grassed swales - are not only designed to convey stormwater runoff, but also to provide some level of treatment through the trapping of sediments and nutrients. The physical dimensions of a swale, in particular its slope and the height of the grass determine its effectiveness in trapping such pollutants. The effectiveness of grassed swales decreases rapidly as the slope approaches 4%. Swales are often used to convey stormwater to another treatment device such as a biofiltration system.

Trash Racks - in-line devices, typically a metal structure in a stormwater channel, that only capture or prevent large water-borne debris and litter moving downstream or entering a river, wetland or lake. It may have an aesthetic impact on receiving waters, but has a negligible water quality benefit on stormwater. The removal percentage only refers to gross pollutants. It is rarely used at the lot level.

The following table outlines the inputs required for each of the treatment measures. All other parameters are preset and so cannot be changed.

Stormwater Treatment Measure	Required Input
Trash Rack	Gross Pollutant (GP) Removal Rate
Below Ground Litter Trap	GP Removal Rate
Green Roof	Surface Area
Buffer Strip	Buffer as % of Impervious Area (minimum of 5%)
	Buffer Area (m²)
Swale	Width (m)
	Slope (%)
	Length (m)
Porous Pavement	Surface Area (m²)
	Filter Depth (m)
Biofiltration	Surface Area (m²)
	Extended Detention Depth (m)
	Filter Depth (m)
Cartridge Media System	TSS Removal Rate (%)
	TN Removal Rate (%)
	TP Removal Rate (%)
Infiltration	Surface Area (m²)

Results

By clicking on the Run button the model is run and a results page within s3qm is shown highlighting if the treatment meets the objectives set, whether they are the NorBE or user specified WQOs. Note that if the treatment area is too large or too small for the area being modelled, you will receive a warning that the hydraulic loading rate is not appropriate. The error box is shown in the figure below. If this occurs, you should go back to the treatment tab for the relevant catchment and adjust the size of your system, or reduce the area draining to it.

Other errors such as discrepancies in areas of catchments may also appear if the are not consistent and will also need to be addressed.

The s3qm model can be run to calculate the results and a certificate can be printed out and submitted to the reviewing authority.

Saving Files

Files can be saved at any point during data input. Click on the Save button in the area you are editing. This saves all the information which can be reopened when required.

Case Studies