Why, despite rapid global movements towards sustainable drainage, are many new developments still bogged down in traditional paradigms?
Management of water is a major challenge for modern societies – and one that the average person tends to take for granted until they’re knee-deep, or the tap runs dry or dirty. That’s when the mud will fly in the direction of designers, developers, authorities and regulators who haven’t moved towards ensuring sustainable infrastructure and water management. When it comes to reputation, mud tends to stick.
With climate projections predicting more intense and frequent weather events such as floods and droughts and heatwaves, and with regulators and authorities delivering increasing environmental penalties, every development must factor sustainability and resilience into its water and drainage design or face increasing costs.
Over recent decades, knowledge of sustainable drainage systems (SuDS) or water-sensitive urban design (WSUD) methods and techniques has matured, and many examples around the world have demonstrated great success and benefits for the environment and communities. These environmental and social benefits are very real, and are certainly valued by communities and regulators, but they can be hard to quantify in monetary terms except by considering the costs of remediating the alternative scenarios, such as dealing with pollution, or cleaning up flood damage.
For designers and developers, the slow rate of adoption of sustainable solutions is likely due to a combination of factors, including preferences for the familiar, a perception of higher costs of construction compared to traditional approaches, and a lack of comprehensive understanding of interactions in a wider catchment.
The good news is that sustainable drainage features can be easily integrated into urban development without undue excess cost. Even at a very small scale, sustainable drainage can provide significant benefits in terms of water quantity, water quality, amenity and biodiversity.
Defining sustainable urban drainage solutions
In essence, sustainable drainage is about coping with the quantity of water (such as how to handle large volumes of rainfall and stormwater to avoid flooding) as well as preserving or improving the quality of water (such as by filtering pollutants and contaminants out of stormwater before it returns to waterways).
Urban development replaces natural ‘soft’ surfaces with artificial and nonabsorbent ‘hard’ surfaces. This means that rainfall and runoff can no longer soak into the ground and instead need to be captured and transferred away. Traditional drainage systems do little to prevent the runoff mixing with sediment and other pollutants, so adequate water treatment is needed for urban runoff, and that comes at significant cost.
Sustainable drainage alternatives allow integration of more ‘soft’ surfaces which can act as sponges and filters. This restores some of the natural elements of the water cycle. Water is able to be stored or slowed, which helps prevent flooding and promotes absorption. The permeable surfaces and vegetation also provide a series of simple treatment stages to maintain or improve water quality, including filtration, insect and microbial activities, and UV radiation.
Sustainable road drainage involves greater use of swales and permeable paving, alone or in combination. For buildings, sustainable drainage practices move beyond the traditional methods of diverting water from roofs and driveways into the underground stormwater system, and embrace features such as green roofs and rain gardens which reduce the speed and quantity of runoff and provide natural filtration for better water quality. Swales can be combined with these features to collect the drainage from individual buildings.
Many of these features can be integrated into developments at comparable construction and maintenance costs to traditional approaches.