Benefits

The parking lot at Toki produces large amounts of runoff during rain storms and spring snowmelt.  Because there is almost no slope, plus an underlying clay soil, the water would create an enormous puddle in the parking lot that persisted for days.  This mega-puddle, dubbed "Lake Toki," was an annoyance and hazard for teachers and visitors alike.

Parking lot at Toki Middle School, Nov. 17, 2013.

On a visit to Toki in 2013 looking for rain garden locations, David Thompson realized that a rain garden located along the edge of the parking lot could drain Lake Toki and eliminate the problem.  With a basin located lower than the parking lot, the rain garden drains the parking area immediately.  After the storm, the roots of plants in the garden provide a pathway for water into the ground through otherwise impervious clay.

"Impervious surfaces" are the bane urban streams and lakes.  These surfaces are the pavement and roofs that cause rainwater to quickly flow to the stormwater system.  The main result of rapid runoff is flooding after a storm, when all the dirt, salt, oil, brake dust, and pet waste winds flushes to our lakes.  Another result is that rainwater can't soak into the ground, causing springs and creeks to dry up.  Rain gardens are one way to restore health to urban waterways.

Benefits of rain gardens

• Soaks rainwater into the ground, replenishing lakes and streams with clean spring water.
• Slows runoff and helps prevent flooding.
• Provides habitat for wildlife (mostly insects).
• Increases biodiversity (especially if native plants are used).
• Traps pollutants and cleans the air, improving community health.
• Beautifies the neighborhood.
• Encourages neighbors to work together, creating community spirit.

Before our rain garden was built, this area was mostly bare dirt, because it was too shady for grass to grow.  Bare soil led to dust blowing about on windy days.  Uncontrolled runoff was also causing an ugly gully--and more dust.  Now the garden prevents dust and turns any muddy runoff that enters the garden into soil.  In addition, foliage of plants in the garden filters dust and other pollutants from the air.  Air pollution is a threat to public health that most people underestimate.

Green areas improve student performance

A scientific study found that "Green spaces have a range of health benefits, but little is known in relation to cognitive development in children. This study, based on comprehensive characterization of outdoor surrounding greenness (at home, school, and during commuting) and repeated computerized cognitive tests in schoolchildren, found an improvement in cognitive development associated with surrounding greenness, particularly with greenness at schools. This association was partly mediated by reductions in air pollution. Our findings provide policymakers with evidence for feasible and achievable targeted interventions such as improving green spaces at schools to attain improvements in mental capital at population level."   Link to source.

Rain gardens soak up stormwater

First the garden traps the rainwater, then it soaks in.  The deep roots of native plants provide a pathway into the soil.  Even before the water soaks in, the plants absorb runoff and store some of it in their tissues.

I watched how both rain gardens worked during a number of heavy storms.  Within about five minutes from the start of a downpour, water begins to rush from the playground's pavement into the upper rain garden.  Even after the water flows in, it doesn't immediately reach the downstream end of the first garden, because the plants are absorbing it.  The water magically vanishes!  Once the plants drink their fill, the garden begins to fill with water.

After about 15 minutes, the first garden begins to overflow.  From there, runoff flows to the second garden downhill.  Again, it takes 15 minutes or more for the plants to drink and for the basin to fill.  It's rare for the second garden to overflow--the two gardens stop all the runoff except in the most severe storms.