The sound of the rain on your roof, lovely umbrellas, the gorgeous smell, going out looking for puddles in your wellie boots…

Traditionally when we develop new urban areas we put a whole series of pipes under the ground to capture all of the stormwater running off from the new surfaces (houses, carparks, roads etc.) , which takes all the water away somewhere else to be managed.

Stormwater is water flowing over ground surfaces in natural streams and drains as a direct result of rainfall over a catchment.

This comes from the fundamental idea that humans must control the environment in order to make it comfortable for civalised society. So we put massive pipes which supposed to be designed to capture the HUGE rain events, the kind we get once every 100 years or so and fair enough, I don’t want my house being flooded, even if its once a century. The problem is that these systems capture the water from all rain events even the little ones we get somewhat frequently in winter. It was believed that all rainfall events posed a flooding risk due to the dregree of imperviousness of the built environment. Why is that a problem? Surely that is a good thing, design for worse case scenario and everything smaller is neligible.

Well the problems occur when you consider where all this water ends up. Down the stromwater drains on the side of the road, into a pipe and off to some drainage sump, constructed compensation basin, bushland or watercourse. Sometimes this is far away from where it fell, mostly it is not treated to get rid of contaminants (like hydrocarbons from the road), often you get very pretty pipes jutting out over the water, and sometimes it causes erosion because all the water is hitting one spot. To be honest, they don’t seem to be doing a fantastic job, given the unbelievable amount of chaos and flooding of roads that happens everytime we get a heavy rain in Perth.

The idea behind ‘Water Sensitive Urban Design’ is to design developments so that the rains which happen most often are dealt with on site, as close as possible to where they fell through either infiltration or water capture and reuse leaving only high intensity rainfall evenst to be managed in the old way (making it a bit less stressful on them).

Need a quick brush up on the water cycle? High school too long ago? Agreed.

Nice things about Water Sensitive Urban Design;

– Water can infiltrate into the ground close to the source (recharging local groundwater aquifers)

– It results in better water quality as water is filtered by plants (less contaminants reaching the groundwater). Plants are really great at pulling yucky stuff out of water, a bit like artifical kidneys.

– No more fenced-off-ugly-weed-infested drainage areas (can you tell I dont like them?), you know the ones I mean.

– Pretty public open space areas with lovely vegetated swale, emphemeral (dry in summer, wet in winter) creek beds with lovely rocks, living streams, wetlands etc.

– It can encourage and supports the growth of large trees which keep the water table down, which means less salt and other nastiest like Acid Sulfate Soils, provide shade, and habitat for animals, children and children-like-adults.

Here are some examples to demonstrate;

These are drainage areas in a public open space development (wet in winter, dry in summer).These are biofilters, which are designed to capture run off from hard surfaces like roads and such.There are other things included in Water Sensitive Urban Design like rainwater tanks, permeable paving (which allows water to infiltrate it) and more hard engineering like underground litter traps and soak wells.

Most importantly its about designing urban spaces to work with water rather than against it. Use it rather than collect it and get it as far away as possible.

Have a look at the New Waterways website, its full an fantastic info on the subject.

Thoughts? Would you like some bigger scale examples? Let me know.