Eric Suesz
When storms cause flooding, we often want to make water flow as quickly as possible away from the problem. But water is an asset, not a problem.
Just as with traffic on our highways, making the pipes wider and the flow faster doesn’t solve the problem. By holding on to water or controlling how quickly it is released using Sustainable Drainage Systems (SUDS), we can get more utility out of our stormwater, while at the same time treating the symptoms of our over-reliance on carbon-intensive infrastructure.
SuDS mimic nature, helping to manage rainfall closer to where it falls. You can use SuDS to convey water, slow runoff (attenuate) before it enters waterways, store water in natural catchments, allow water to soak (infiltrate) into the ground or even design them so they promote evaporation. Best of all, they are all natural and can help you control and filter out pollutants.
Why SuDS modelling in InfoDrainage matters for compliance
Sustainable Drainage Systems (SuDS) are now fundamental to drainage design across the UK and are becoming more adopted internationally. In the UK, to meet planning requirements and align with the CIRIA SuDS Manual (C753), engineers must demonstrate that sustainable drainage features perform reliably across multiple design storms, including climate change scenarios.
Autodesk InfoDrainage enables engineers to represent, size and optimise SuDS features within a fully integrated hydraulic model — ensuring that design intent aligns with recognised standards and regulatory expectations.
This article focuses specifically on SuDS modelling in InfoDrainage (rather than general SuDS design guidance) and how to ensure your modelling workflows align with CIRIA guidance.
SuDS modelling in InfoDrainage: Representing sustainable drainage features
InfoDrainage supports a wide range of sustainable drainage components within its Stormwater Controls (SWC) framework. Each feature can be configured to reflect physical design characteristics and CIRIA-aligned performance criteria.
Supported features include:
- Rain gardens and bioretention systems
- Swales
- Soakaways and infiltration trenches
- Porous (pervious) pavements
- Ponds and basins
- Green roofs and blue roofs
- Filter drains
- Rainwater harvesting systems
For a broader overview of SuDS feature types and their typical applications, see our high-level guide to sustainable drainage features.
Modelling bioretention and rain gardens
Bioretention systems typically consist of:
- A surface storage layer
- An engineered filter medium
- A drainage layer with underdrain
CIRIA 753 guidance suggests that bioretention filter media commonly have infiltration rates in the range of 100–300 mm/hr, depending on specification.
In InfoDrainage, bioretention systems can be represented by:
- Defining surface storage depth
- Configuring filtration layers
- Assigning infiltration rates (based on site data or specification)
- Including underdrain discharge controls
This allows designers to simulate both treatment-stage storage and controlled outflow behaviour within the wider network model.
💡 Need to go deeper? We have articles on both Rain Gardens and Bioretention systems.
Modelling swales and filter drains
Swales are linear conveyance features that provide attenuation and treatment. CIRIA recommends considering longitudinal gradients, side slopes (typically no steeper than 1:3), and vegetation roughness.
In InfoDrainage, swales are modelled by:
- Drawing SWCs aligned with the flow path
- Assigning appropriate Manning’s roughness values
- Defining cross-sectional geometry
- Specifying infiltration where ground conditions allow
Filter drains, which include gravel backfill and underdrain pipes, can be represented by adjusting:
- Inflow type (eg, lateral inflow)
- Porosity
- Conductivity values
- Underdrain configuration
This ensures realistic representation of subsurface storage and filtration performance.
💡 Need to go deeper? Read our Swales article.
Modelling porous pavement systems
Porous pavement provides distributed source control and temporary sub-base storage. CIRIA guidance emphasises:
- Adequate sub-base thickness
- Sufficient porosity (often 30%+ void ratio)
- Consideration of traffic loading
- Controlled discharge or infiltration
In InfoDrainage, porous pavement can be modelled by:
- Defining surface area and runoff contribution
- Using the Quick Storage Estimate (QSE) tool to derive required storage volumes
- Assigning infiltration rates or discharge controls
This supports iterative sizing based on rainfall intensity and discharge constraints.
💡 Learn more in our article about Porous (pervious) pavements.
Representing soakaways and infiltration trenches
Infiltration-based systems must comply with BRE 365 testing and demonstrate adequate drawdown (typically within 24 hours).
In InfoDrainage, these systems can be represented by:
- Assigning site-specific infiltration rates
- Applying appropriate factors of safety
- Testing multiple storm return periods
- Confirming drawdown time within simulation outputs
CIRIA recommends applying safety factors to account for long-term clogging and uncertainty. InfoDrainage allows designers to incorporate these factors directly within infiltration parameters.
💡 We have in-depth articles about Soakaways and Infiltration Trenches.
Modelling ponds and basins
Ponds and attenuation basins provide downstream storage and staged treatment. CIRIA guidance includes:
- Design return periods (e.g., 10-, 30-, 100-year storms)
- Freeboard allowances
- Side slopes typically no steeper than 1:3
- Sediment forebays where required
In InfoDrainage, ponds can be sized using:
- Storage depth inputs
- QSE calculations
- Discharge control structures (orifice, weir, vortex control)
- Scenario-based rainfall simulations
This enables performance verification across multiple storm durations and climate change allowances.
💡 Read more about designing Ponds.
Green roofs and blue roofs in InfoDrainage
CIRIA guidance notes that extensive green roofs may provide limited depression storage, often approximated as around 5% of substrate depth, though performance varies depending on substrate composition and evapotranspiration rates.
In InfoDrainage:
- Green roofs are typically modelled as runoff sources with adjusted runoff coefficients and depression storage
- Blue roofs can be represented as controlled storage units with defined outflow structures
This allows designers to incorporate roof-level sustainable drainage strategies within a full-site hydraulic model.
A CIRIA-aligned SuDS modelling workflow
A structured workflow in InfoDrainage typically follows:
- Import site layout, topography and catchment data
- Define impermeable areas and runoff parameters
- Insert SuDS features using SWCs
- Map CIRIA-recommended parameters to model inputs
- Infiltration rates
- Storage depths
- Slopes
- Manning’s values
- Run simulations across required return periods
- Identify critical storm duration
- Verify greenfield runoff compliance
- Confirm exceedance routing
- Generate calculation reports for submission
This approach ensures that SuDS features are assessed as an interconnected management train rather than isolated design elements.
Best practice considerations
To improve modelling robustness:
- Use site-specific infiltration data wherever possible
- Assess multiple storm durations to identify true critical events
- Confirm drawdown performance for infiltration systems
- Apply appropriate safety factors
- Document assumptions clearly within exported reports
Integrating recognised CIRIA guidance with digital hydraulic modelling improves both technical defensibility and regulatory confidence.
From standards to submission-ready outputs
When it comes time to output your reports, InfoDrainage supports:
- Critical duration analysis
- Climate change scenario testing
- Attenuation volume optimisation
- Greenfield runoff verification
- Automated reporting for planning submission
By aligning SuDS representation with recognised standards such as CIRIA C753, designers can reduce redesign cycles and streamline regulatory approval.
Continue your SuDS design journey
- Learn about SuDS features and design principles. Read our Sustainable Drainage Features guide.
- Model SuDS workflows in InfoDrainage yourself. Start a free 30-day trial (no credit card required)
- Download our Guide to Representing SuDS in InfoDrainage in accordance with the SuDS Manual Ciria 753.
- Dig into the InfoDrainage Technical Information Hub and examine how the software conforms to industry standards.