Tuesday, November 26, 2013

Akira Toki School--stormwater problems & rain garden locations

I had a chance to observe the parking area and athletic field during moderate rain on November 17.

Carlene Bechen told me that stormwater puddling in the parking area was a problem.

The puddling is caused by...

  • A large area that collects runoff--especially the large parking area closer to the school.  Parts of the athletic field, and the walkway between the woods and the school, also contribute runoff.
  • A very gradual slope in the drainage way.  The puddle should drain to the west.
Puddling is not caused by a shallow water table.  Since the school is located on the "divide" between drainage basins, the water table should be well below the surface.

The parking area should drain to the west, but the slope is too shallow.
  • Utility maps should be checked for an existing stormwater drain underground.  There may be one that has become clogged or buried.  I saw no sign of a drain.
  • Digging a shallow ditch or swale to the west is an obvious solution, but would be expensive.
  • A rain garden just north of the puddle location would drain the puddle, except during winter.  Additional rain gardens "upstream" would reduce water flowing into the puddle.
The rain garden's basin would be lower than the parking lot.  This would draw off water, until the basin is filled.  After that, the plants will absorb water, and their roots will channel it into the ground.

A rain garden would do more than eliminate the puddle.  It would increase biodiversity, which brings educational and health benefits.

A second rain garden at this location would reduce runoff going to the puddle, and would stop erosion.

Small rain gardens could be located below downspouts.

Puddle area during the summer of 2013.

Photos showing stormwater opportunities elsewhere on school grounds.

Friday, November 22, 2013

Lincoln School--stormwater problems & rain garden locations

I observed the school twice during moderate rain.

Parking area

The main parking area has a perfect spot for a rain garden, with no excavation required!  The parking area drains to the north, into a swale (depression) between the parking and the sidewalk.

This swale was designed to infiltrate stormwater--so why do you need to do anything?  First, the gaps in the curb that admit water to the swale are blocked in many places by debris or weeds.

Second, grass in the swale is not very effective in infiltrating water.  From the pattern of debris (below), you can see that in heavy rain, the swale is completely overwhelmed.

It floods heavily, then overflows the drain and out into the street.  In heavy rain, the swale is simply not working.

To hugely improve how the swale works, simply plant it with prairie (or rain garden) plants.  You may need to create some shallow dams along the swale, to slow the runoff.  No sweating to dig a basin is required!

The swale could be planted in segments--a small addition each year until the whole swale is done.

Paved playground

Teacher Josie Igielski.said that stormwater pools here.  During winter, ice prevents children from playing on some areas.

I looked to see if runoff could be diverted before it reaches the playground.  The answer is no--there are no downspouts emptying into the playground area.

All the water that pools comes from the paved playground itself.  The pooling results from the very gradual slope of the surface, which isn't enough to drain the area quickly.

However, there is some backup of water at the southern edge of the playground, where raised turf makes a low dam.  Digging some ditches here, or placing a rain garden at the edge, would prevent pooling there.  But ditching or rain gardens would not prevent ice or pooling in more central areas of the playground.

A concrete gutter drains water to the east (right).

The east end of this gutter is clogged with leaves or turf--which should be cleared out.  But this would only reduce flooding during very severe storms.

To prevent ice buildup on the playground during the winter, I recommend...

  • A ditch or garden where water pools at the edge (see above).
  • Always clear the playground as soon as possible after any snow, even very light snowfall.  This will help the sun to evaporate any remaining snow and ice--even if temperatures are below freezing.
  • If meltwater accumulates during the day, sweep any pooling water towards the south drain with a large broom.
Of course, you can't clear the playground by hand after a heavy snow.  But we rely on mechanized equipment and salt too much.  Ten kids with brooms could be surprisingly effective, for light snows or days when snow is melting and pooling.

Summary--good rain garden locations

  1. Along S border of paved play area, where water pools to the E
  2. Same, were water pools next to the round stormwater inlet.
  3. In the swale that borders the parking area.  This one has the potential to infiltrate the most water, for the least effort.