[Free Download] The hidden hazard: Why effective surface drainage is key to walkable public spaces

As Australian cities increasingly prioritise people over cars, the push for more walkable urban spaces is gaining momentum. The benefits are well-documented, with reports from firms like Arup highlighting that walkable cities are not only healthier and less polluted, but also safer, more social and economically productive. One study found high-ranking walkable cities boasted a one-third higher GDP per capita. 

However, beneath the surface of this ideal lies a persistent and costly hazard: poorly managed stormwater. In Australia, annual bodily injury claims from slips, trips and falls can total more than $400 million, with liability often extending to the engineers and architects behind the design. 

These incidents are often preventable. For engineers, designing safe, functional and durable public pavements requires moving beyond traditional methods and embracing a holistic approach where surface water management is a core consideration from day one.

A case for the flat and level

For decades, the conventional approach to draining a paved area was to create complex four-way slopes funnelling water towards a series of point drains. This method, however, results in undulating surfaces that can be hazardous for pedestrians, create puddles and deteriorate prematurely. 

A safer, more effective solution lies in designing flat and level pavements with gentle, one-way gradients. This approach relies on high-efficiency linear trench drains to intercept and remove surface water continuously.

“The pavement itself must be considered a part of the drain,” said John Sordo, Manager of Marketing and Product Management at ACO. “A flat surface with gentle gradients is much safer and more convenient for users.” 

These level surfaces provide greater versatility, allowing for activities like outdoor dining and cycling, and their simpler construction leads to improved pavement longevity. A case study by Rider Levett Bucknall found that pavements using precast trench drains were more cost-effective to construct than those with point drains or cast-in-situ options, delivering savings in construction, maintenance and design life.

Balancing competing design demands

While linear drainage is key, several critical engineering trade-offs must be managed to ensure a pavement is both safe and hydraulically efficient.

One of the most important is the grate’s slot width. Wider openings improve the rate of water capture but increase the risk of trapping heels, bicycle wheels and the tips of walking canes. Narrower slots are safer for pedestrians but can compromise hydraulic performance and are more prone to clogging. Navigating this requires careful reference to Australian Standards.

Another common misconception relates to slip resistance. A higher slip rating is not always safer. 

“If you have a grate that is more slip resistant than the rest of the pavement, it creates a trip hazard,” Sordo said. 

The safest solution is to ensure the grate and the surrounding surface have the same level of slip resistance, as specified to AS 4586 Slip resistance classification of new pedestrian surface materials. 

Designing for durability and impact

A drainage system is an integral part of the pavement, and its failure can create an immediate safety hazard. Therefore, specifying for strength and durability is critical to ensure the drain’s service life matches that of the pavement. 

Engineers must consider the intended use of the area – from pedestrian-only zones to areas with heavy, turning trucks – and select a system with the appropriate load classification as defined in AS 3996. Environmental factors, such as proximity to the coast or the use of cleaning chemicals, will also influence material selection. 

Ultimately, successful public spaces depend on engineers getting these details right. By treating surface water management as a fundamental design element, it is possible to create pavements that are not only efficient and durable but also safe, accessible and aesthetically pleasing.