Lifestyle: Swale use a watershed in drainage solutions

It is encouraging to see the number of people engaging in meaningful dialogue about important local issues through the letters page of the Chronicle.

Sadly, too often these letters include references to failed attempts to work with Wanganui District Council on strategies that work with nature instead of against it.

For some reason, our council appears stuck in the past on many issues of infrastructure and economic development. From most accounts, the 1950s were a great time to be alive, but in many cases these days 50s' thinking no longer applies.

So it is particularly significant that council chief water engineer Kritzo Venter has been active and vocal about promoting progressive water management strategies that "mimic" those that nature itself has developed over millions of years (that is some investment in R&D, ain't it?).

One of those water management strategies, swales, has been in use for decades in some places around the world.

A swale is a long, narrow earthwork that runs perpendicular to slope. They slow the flow of surface runoff and facilitate infiltration into the ground. They are perfectly level, unlike ditches, which are sloped to drain water away like a river.

Water in a swale soaks into the ground instead of running over it. A carefully-constructed swale includes a level-sill spillway that gently allows it to be overtopped in a controlled manner in the event of extreme rain.

The use of swales is the type of win-win-win situation I write about in this column.

It reduces stream and river levels during flood events.

It increases groundwater reserves that can be called upon during periods of drought.

And significantly, it reduces the overall cost of infrastructure - eco-thrifty at its best.

For example, two years ago I was asked to consult on a proposed residential development in Kaiwhaiki that had significant drainage problems.

I was told the 10-year-old quote to solve the problem the old way using pipes and culverts was for $500,000.

After picking my jaw up off the floor, I told them that good eco-design, which would include cluster housing and the use of swales, would significantly slash that price.

The other strategy promoted by Kritzo Venter - and praised by Chronicle deputy editor Anna Wallis - is the use of rain gardens.

A common use of rain gardens is to absorb and filter runoff from new parking lots or other such impermeable surfaces. In this way, rain gardens function like wetlands: sponging up excess water and cleaning it through natural processes.

I first learned about rain gardens in 2005 while taking a certificate programme in the United States on organic land care. Shortly thereafter I advised a school to install rain gardens in a number of locations where they had persistent drainage problems. It became a relevant learning experience for students.

In 2009, while living in Raglan, I built a small management system to control an excess of runoff coming from the roof of a newly-built outdoor kitchen at a campground.

The system consisted of a swale, a level-sill spillway, and a rain garden. We planted the swale with feijoa trees and the rain garden with plants that tolerate periods of wet and dry.

While in Raglan, I also used swales as a metaphor for eco-design during a Pecha Kucha night, where artists and designers share their work through 20 slides with narration of 20 seconds per slide.

That presentation, Thinking Like a Swale, became the inspiration for a programme I offered at the Josephite Retreat Centre earlier this year to acknowledge the United Nations year of water.

Hopefully, when River Week 2014 comes around next year, I'll get a chance to present it again to complement and support the education efforts Kritzo has already made in the community.

Nelson Lebo consults businesses, schools, and home-owners on all aspects of sustainability - email: theecoschool@gmail.com or phone 06 3445013 or 022 6350868.