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Harvest Storm (D)rainwater with “Soil Sponges”

March 07 2014 | Ocean Friendly Gardens, Lawn Patrol,
by Paul Herzog

Rainwater falling off a roof like a waterfall onto a sidewalk, then to a stormdrain: it's too valuable to waste (pictured at right and below). Rainwater is a resource in Ocean Friendly Gardens, whether they're landscapes, street trees or parking lot planters.

Removing sections of concrete and asphalt and creating "soil sponges" can slow, absorb and filter water. This helps to reduce pollution, flooding and the need for imported water. It's helpful in dry months, too, when more runoff occurs due to sprinklers that overshoot into streets or are broken, or people washing off cars or driveways.

How much can we harvest? As this link on the OFG homepage says, 600 gallons of water is generated by every 1-inch of rain that falls on 1,000 square feet of hard (impervious) surface.

To get a sense of how much water landscaping can need, a 1,000 sq. ft. grassy yard uses approximately 30,000 gallons of water a year. In a warm climate like Monrovia, CA, every square foot of a 1,000 square-foot yard of cool-season turf grass needs 57.06", equalling 35,000 gallons. Imagine if it's a 10,000 sq. ft. yard: 353,772 gallons! Add to this that as much as 50% of water is wasted due to inefficient irrigation.

How do we utilize it? Low Impact Development (or Design), or LID, is typically just removing concrete and asphalt and creating an OFG. It's just landscaping. Healthy, biologically-active soil acts like a sponge to: filter pollutants, absorb water for use by plants, and let excess water flow down to acquifers or laterally to creeks and rivers.

The OFG parkway curb cut (one of four in this parkway), at right, sponged up its part during the last rain. Click here to read about how the residential curb cut happened.

The school OFG pictured at left used to be mostly asphalt, and instead absorbed and filtered lots of the recent rains. Click here to read more about how that project happened.

What could not be absorbed by both was directed off site...and someday to another OFG!

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