STORMWATER Management Plans

Stormwater Drainage Design - Water Sensitive Urban Design - Water Quality & QUantity

What is Stormwater?

Stormwater is runoff from a rainfall event, and includes any material (such as sediment, debris or pollution) that mobilised in the path of flow.

The Natural

In a natural undeveloped catchment, the stormwater generated is largely infiltrated or absorbed into the soil and sub-soil (pervious surfaces), with any excess flows forming overland flow paths, intermittent watercourses or permanent streams.


The built environment interrupts this natural water cycle balance. Impervious surfaces such as pavements, car parks and rooftops rapidly shed rainfall whilst preventing infiltration. Unmanaged, stormwater events in urban catchments can result in flooding even during low-rainfall-intensities; run-off is often concentrated with increased peak-flows and higher runoff volumes.

The impact

The cumulative impact of unmanaged stormwater to a development (and surrounding properties) can range from recurrent nuisance, increased flood risk to significant damage. Lack of stormwater management can cause a development to degrade downstream ecosystems, exceed infrastructure capacity and underutilise a valuable natural resource.

What is Stormwater Quantity management?

Stormwater quantity management investigates the hydrological and hydraulic characteristics of a proposed development and presents a strategy to mitigate potential stormwater impacts. This includes the use of control devices, systems and procedures to convey, store and/or detain stormwater.

Solutions can include conventional “hard” structures such as tanks, pipes, pits and culverts, or ‘soft’ drainage elements such as swales, ponds and basins.

Traditionally, stormwater has been viewed as a source of nuisance and hazard to be removed as quickly and cheaply as possible. This approach often led to significant infrastructure, with limited consideration to then downstream environment and future economic impacts.

At Broadcrest we embody a contemporary approach to stormwater. Our engineers deliver on pragmatic and cost-effective design, integrating water management into the overall development. This approach allows for:

  • Reduced Run-off and Peak Flows
  • Management of Flood Risk
  • Enhanced Environmental outcomes
  • Stormwater Harvesting and Reuse
  • Integration of BASIX Requirements
  • Lower Intensity Design
  • Integration of Stormwater and Landscaping
  • Additional Environmental Value with Reduced Development Costs

Broadcrest specialise in modern design practices and software (including DRAINS, XP-RAFTS, HEC-RAS, QGIS and RORBS) to tailor efficient solutions to satisfy client needs, all whilst working within local government frameworks and national standards.

Our team also provides field services including permeability testing, feasibility studies and site classifications to assist in all your stormwater management needs. Follow the link below to see Broadcrest’s full list of stormwater quantity capabilities.

Stormwater Quantity

Drainage | Flow | Capture

What is Stormwater Quality Management or WSUD?

Stormwater quality management is the process of implementing water quality treatment principles, systems and management practices to minimise the impact of a development on the downstream water cycle. Stormwater quality management is often provided with, and incorporated into, a development’s drainage or stormwater quantity design. Synonymous with Water Sensitive Urban Design (WSUD), stormwater quality design emphasise:

  • Protection of natural ecosystems
  • Protection and improvement of water quality draining from developments
  • Restoration of urban water balances
  • Infiltration and groundwater Recharge
  • Conservation and reuse of water resources
  • Integration of stormwater treatment into landscapes and developments
  • Reduction in peak flows and runoff volumes to predevelopment levels
  • Developing public, environmental and recreational assets
  • Efficient and cost-effective design and implementation

To ensure effective water quality treatment, local and state government bodies provide stormwater quality objectives in the form of minimum pollution reduction targets that a development must achieve to gain approval. Common pollutant types and example sources include:

  • Suspend Solids (SS) - Weathering, pavement and land surface erosion
  • Nutrients - Total Phosphorus (TP) & Total Nitrogen (TN) – Erosion of organic matter, animal faeces, detergents
  • Grose Pollutants – Litter, organic matter, construction activity

Stringent guidelines also exist for developments within NSW drinking water catchments in which Neutral or Beneficial Effect (NorBE) to water quality must be demonstrated. Lsearn more about the Water Sensitive Urban Design (WSUD) options for your site see the link below.

Stormwater Quality

Treatment | WSUD | Sustainability

How to achieve Stormwater Quality Targets

Stormwater quality improvement devices are a standard feature of WSUD and stormwater quality management to treat stormwater at the pollutant source. Often a single device is not sufficient, so multiple treatment devices are used in series to form a ‘treatment train’ to achieve the necessary water quality objectives. Examples of stormwater quality treatment measures and Best Management Practices (BMPs) include:

  • Bioretention basins, raingardens & infiltration trenches
  • Rainwater tanks, detention & sedimentation basins
  • Grassed swales and vegetated filter strips
  • Ponds & constructed wetlands
  • Sand filters and Grose Pollutant Traps (GPTs)
  • Proprietary primary, secondary and tertiary filters
  • Permeable pavement and soft landscaping

To ensure the efficient design and achievement of stormwater quality objectives, Broadcrest specialise in MUSIC and s3qm water quality modelling software & services. Learn more about Broadcrest’s comprehensive range of stormwater services:

Stormwater Quantity

Drainage | Flow | Capture

Stormwater Quality

Treatment | WSUD | Sustainability

Soil & Water Management

Prevent | Stabilise | Control

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