On March 4th, Smart Water Magazine and Autodesk Water hosted the webinar Efficient Drainage Modelling for Housing Developments: Best Practice Case Study, part of the Autodesk Water Webinar Series. The session brought together industry professionals to discuss how digital tools and practical workflows can improve drainage modelling for housing developments.
The webinar featured Simon Renfrey, Business Development Manager at Symetri, and Brian Jones, Associate Engineering Director at Newland Homes. Furthermore, Idris Nujjoo, Technical Solutions Engineer at Autodesk Water, moderated the Q&A session.
The discussion focused on the increasing challenges engineers face when designing drainage systems for modern housing developments. Sites are becoming more constrained, planning requirements are growing, and sustainable drainage systems, or SuDS, are now expected in most new developments. These conditions make traditional spreadsheet-based approaches difficult to maintain and increase the risk of errors in design and analysis.
Simon Renfrey opened the session with an overview of Symetri and Autodesk Water solutions. He explained that many organisations in the water and construction sectors are moving toward more integrated digital workflows. These workflows combine modelling tools with design platforms and data management systems to support more reliable decision-making.
Renfrey noted that Autodesk solutions such as InfoDrainage and InfoWorks ICM support various stages of the water management process. InfoDrainage is typically used for site-level drainage design, while InfoWorks ICM supports broader flood modelling and catchment scale analysis. According to Renfrey, the integration of these tools with platforms such as Civil 3D allows engineers to move from concept design to detailed modelling within a connected workflow.
“Our focus is on helping teams to produce clear, compliant, review-ready submissions first time, aligning local authority expectations to minimise back-and-forth redesign and project delays" - Simon Renfrey
He also highlighted some of the common difficulties that drainage engineers encounter. These include incomplete site information, increasing regulatory scrutiny, and the tendency to create overly complex models. In many cases, teams still rely heavily on spreadsheets, which can lead to inconsistent calculations and inefficient design processes.
The technical portion of the webinar was led by Brian Jones, who presented a real-world case study based on a residential development in Pittville, Cheltenham. The site was previously part of a school playing field and has since been repurposed for housing development. The project also helped fund a new sports facility for the school.
Jones used the project to demonstrate how his team approaches drainage modelling in practice. He began by outlining the typical design process. The first step involves reviewing existing site information and identifying missing data. This often requires gathering service records, conducting topographic surveys, and carrying out ground investigations. Site visits are also important to understand constraints such as access points, discharge locations, and existing utilities.
Once this information is collected, engineers can begin developing an outline drainage strategy. A key step is calculating the greenfield runoff rate, which defines the allowable discharge from the site after development. Jones then demonstrated how preliminary storage requirements can be estimated.
Using InfoDrainage, Jones showed how engineers can import CAD data, surface models, and drainage networks to create a working model. However, he stressed that models should remain simple and focused on key features. Importing excessive data or modelling every pipe segment can increase file sizes and introduce instability in simulations.
“Don’t overcomplicate the model,” Jones said. “Remember it’s a model, not reality.”
The presentation also covered several practical modelling steps. These included importing inflow areas, defining stormwater controls, and applying hydraulic structures such as hydrobrakes to regulate discharge. Jones explained how the network design wizard can be used to optimise pipe sizes based on design criteria such as rainfall profiles and return periods.
Using InfoDrainage, Jones showed how engineers can import CAD data, surface models, and drainage networks to create a working model
Jones also discussed how the design evolved during the planning process. The original discharge point was changed from a sewer connection to an open ditch on Albert Road. The revised scheme also introduced rain gardens and filter trenches to improve drainage performance and reduce the required pond volume.
During the Q&A session, led by Idris Nujjoo, attendees asked questions about modelling approaches, rainfall data, and regulatory challenges. Jones explained that engineers often start feasibility studies using older FSR rainfall data because it is freely available. However, most detailed designs now use FEH rainfall data, which provides more accurate local rainfall information.
Another topic raised by participants was the difficulty of gaining approval from local authorities. Jones explained that one challenge is fitting SuDS features into tight development sites, particularly when highway authorities prefer not to maintain them within road corridors.
In their concluding remarks, Renfrey emphasised the importance of adopting structured digital workflows and ensuring that SuDS features are incorporated thoughtfully into site designs. Jones echoed this view, stressing that careful modelling and thorough checks remain essential for reliable drainage design.
