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.

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