El Niño in the garden

In October, a typhoon dropped four inches of rain on downtown Oakland, CA in twelve hours, and the “Pineapple Express” has brought lots of rain ever since. The rains brought permanent mud puddles to the Casita–until students at a February rainwater harvesting workshop dug a rain garden.

We first dug a channel between the casita and the chicken coop–as far from the slab “foundation” as possible. Now rain runs away from the slab, rather than under it!

grading soil around building

Digging diversion channel and grading so that water flows away from slab

Using a bunyip–a water level made from clear vinyl tubing and scrap 1 x 2–we made sure that the broad channel sloped down at a 2 % to 4 % grade. Sedges and wildflowers will eventually inhabit the channel (Landscape architects call this a diversion swale).

using a water level

Using a bunyip to check channel slope and level the berm

Rain runs down the channel into a rain garden–a basin large enough to hold 200 gallons, or 1″ of rainfall on the casita roof. The soil here is heavy clay, so I decided to dig a 18″ (30 cm) deep basin, then fill it in with 12″ (25 cm) of well-draining soil. We used a mix of 30 % native soil (which is approximately half sand and half clay), 30 % sand from Alameda Beach, and 40 % compost from our bin. I want the rain garden to drain within 24 hours–any longer and it would attract mosquitos. The berm around the rain garden is level, except for a low spot that acts as an overflow in typhoons or extended storms. The overflow on my rain garden sends water towards a blueberry bush.

shallow ditch sloping to rain garden

Water flows down the shallow channel to the rain garden basin

We chose plants based on our observations of plants growing along Sausal Creek–rushes, lupine, (miniature) cattails, and creek monkeyflower, for starts.

rushes, lupine, and monkeyflower

Riparian plants tolerate flooding--plant ones that like less water higher in the rain garden

A few weeks later, the rain garden filled up in an overnight storm. The water sank in after 4 hours.

rain garden full of muddy water

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~ by waterunderground on March 23, 2010.

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