Sector Pathways › Stormwater & Urban Runoff
Stormwater & Urban Runoff
Stormwater and urban runoff are intermittent, high-flow streams whose volume and quality change with rainfall, catchment use, antecedent dry periods, sediment, hydrocarbons and spills. The required response depends on what should be controlled at source, captured, bypassed, treated, reused or discharged.
A pathway for event-driven runoff
Runoff volume and quality vary with rainfall intensity, antecedent dry periods, surface use, construction activity, spills, sediment and hydrocarbon sources. Not every event or drainage stream should be captured or treated in the same way.
We work with owners, operators and project teams to define source controls, catchment segregation, capture and bypass logic, storage, treatment, outlet routing and monitoring before equipment is selected.
Stage 1
Define catchment and event basis
Confirm contributing surfaces, drainage connections, design events, initial runoff conditions and bypass requirements.
Stage 2
Control solids and hydrocarbons
Set gross-solids removal, settling, filtration or oil separation against the hydraulic and contaminant load.
Stage 3
Store, treat and route selected runoff
Match storage and treatment to the required discharge condition or a defined non-potable receiving duty.
Stage 4
Operate and verify across events
Define drawdown, inspection, sediment removal, sampling and post-event maintenance requirements.
Where runoff management planning begins
The starting point is a catchment and event basis: contributing surfaces, drainage connections, pollutant sources, design rainfall, initial runoff behaviour, bypass conditions and storage drawdown.
Recovery depends on whether selected runoff can be stored, treated and used before the next event. Capturing all runoff can enlarge storage and treatment without adding useful recovery.
Potential project gains
- Treated runoff directed to irrigation, washdown or another defined non-potable duty where viable
- Reduced solids, litter and hydrocarbon loading to drainage and receiving waters
- Better control of discharge quality, bypass and overflow during selected events
Conditions that define the route
- Catchment area, surface use, drainage segregation and runoff volumes
- Event frequency, intensity, duration, antecedent dry period and initial runoff quality
- Sediment, litter, hydrocarbons and site-specific contaminant sources
- Storage drawdown, bypass, overflow, outlet and maintenance arrangements
The project basis is established from catchment, event and outlet conditions, not from storage volume or a nominal first-flush percentage alone.
Stormwater capture and treatment planning
The assignment connects catchment conditions and outlet requirements with source controls, drainage, capture, bypass, storage, treatment, residuals handling, operation and performance requirements needed for supplier engagement and implementation.
Advisory
Define the catchment and outlet basis
- Confirm contributing catchments, pollutant sources and drainage connections.
- Define design events, capture and bypass logic, reuse duties or discharge requirements.
- Prepare performance requirements that suppliers can price and compare on a common basis.
FlowPlan
Develop the connected runoff route
- Map source controls, collection, gross-solids removal, settling, hydrocarbon control, storage, polishing and outlet routing.
- Define bypass, overflow, drawdown, residuals removal and off-spec arrangements.
- Align hydraulic duties, controls, monitoring and commissioning checks across supplier proposals.
Typical modules: Clari+ OxiClear+
Specialist
Resolve event hydraulics and contaminant risks
- Confirm runoff coefficients, peak flows, initial runoff quality, sediment and hydrocarbon loads.
- Assess receiving-water sensitivity, reuse quality and treatment limits.
- Review access, sediment removal, maintenance, monitoring and post-event inspection requirements.
What defines the stormwater project basis
The basis is confirmed from catchment use, drainage connections, event hydraulics, contaminant sources, storage drawdown, required outlet and maintenance arrangements. These checks determine capture, bypass, treatment, controls and performance requirements.
- Catchment area, surface types, runoff coefficients, contributing land uses and drainage connections
- Rainfall records, design events, event duration, antecedent dry period, initial runoff quality and bypass basis
- Suspended solids, particle size, hydrocarbons, metals, nutrients, pathogens and other site-specific contaminants
- Existing drains, sumps, separators, detention structures, discharge points and upstream source controls
- Storage drawdown, reuse demand, discharge limits, receiving-water sensitivity and off-spec routing
- Space, access, sediment removal, power, controls, monitoring, maintenance and post-event inspection requirements.
Typical stormwater and urban runoff routes
The route depends on catchment use, design events, pollutant sources, available storage and required outlet. The sequence below shows common project logic; individual stages are confirmed from site conditions.
Stage 1
Source control and runoff segregation
Reduce litter, sediment, spills and cross-connections before runoff reaches the treatment route.
Stage 2
Capture, bypass and gross-solids control
Define which runoff is captured, safely bypassed or overflowed, and remove debris and coarse solids.
Stage 3
Sediment and hydrocarbon removal
Apply settling, hydrodynamic separation, filtration or oil separation according to particle and contaminant conditions.
Stage 4
Storage and polishing where required
Provide drawdown and add filtration, adsorption, disinfection or membrane treatment only where the outlet requires it.
Stage 5
Outlet routing and event verification
Define reuse or discharge routing, sampling, sediment removal, inspection and post-event maintenance.
Configuration depends on catchment conditions, event hydraulics, contaminant loads, storage drawdown and the required reuse or discharge quality.
Environmental and operating gains from controlled runoff management
The main gain is controlled runoff that reduces uncontrolled solids and hydrocarbon discharge and, where demand and quality align, provides water for a defined non-potable duty.
The assessment must also account for source control, bypass, overflow, storage drawdown, sediment removal and post-event maintenance. Storage alone does not establish an effective runoff-management route.
- Water recovery: treated runoff directed to a defined irrigation, washdown or other non-potable duty where viable.
- Receiving-water protection: solids, litter and hydrocarbons controlled before discharge.
- Site operation: bypass, drawdown, inspection, sediment removal and monitoring aligned with the site team.
Next steps
If you share the catchment use, drainage layout, event conditions, current controls, intended outlet and available storage, we can identify the assessment and system-planning work most relevant to the site.
Get In Touch
Share the catchment, drainage network, pollutant sources, current controls, intended reuse or discharge condition and site constraints. We will translate these into a defined stormwater assessment and treatment scope that suppliers can price and verify.
- Primary objective: runoff control, receiving-water protection, reuse, treatment upgrade or compliance correction
- Catchment area, surface uses, drainage connections and available rainfall or event records
- Known sediment, litter, hydrocarbon, metal, nutrient, pathogen or spill risks
- Existing sumps, separators, detention, storage, bypass, overflow and discharge arrangements
- Required outlet, monitoring, maintenance, commissioning and acceptance requirements
The form below records the project information needed to direct the enquiry.