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Nine Simple Rain Storage Techniques

Friday February 25, 2011

California rejoices with rain.  Much of our agriculture, development, and industry rely heavily on the snowpack, reservoir levels, and winter precipitation totals.  A “good” year for California is a wet one.

So it is rather ironic when the rain does come to our cities and towns, we treat the water like an unwanted guest and remove it from our sight as quickly as possible.  We direct it to drains and gutters and don’t know or wonder where it goes from there.

But as the water is directed elsewhere, it brings all of the surface pollutants and trash with it on a journey through the watershed, contaminating aquatic habitats and ruining natural spaces along the way.

los angeles river

The mighy LA "river".

In our home landscapes, we treat rain water in about the same, egregious way.  Rainwater is gathered in gutters, piped to downspouts, and directed towards a drain.  It is barely used and rarely honored.  But our landscapes are wonderful assets capable of storing vast amounts of moisture if designed and maintained properly.

Benefits of Storing Rain in the Landscape

Conventional attitudes toward storm water treatment are slowly changing.  Decades of poor decisions have revealed the deficiencies in our current system and the benefits of storing water in our landscape are obvious apparent:

Reduces storm water run-off quantity and velocity:  Many of our surfaces, even in our landscapes, are hard and impermeable.  When rain hits these surfaces it quickly is directed to a low point.  By doing so, the rain picks up speed.  The combination of quantity and velocity of run-off creates major problems downstream that could otherwise be avoided.

When our landscapes are “softened”, they may absorb and retain much more moisture than thought possible.  This sponge-effect greatly reduces the run-off from a site.

Allows for biological and physical treatment of contaminants:  When storm water is moving quickly, the contaminates it has picked up have very little chance to be removed before reaching sensitive areas.  By directing run-off over landscape, an amazing amount of cleansing can occur.  Many plants are even efficient at removing heavy metals and other organic pollutants from run-off.

Allows for infiltration of water > recharges groundwater levels:  Our groundwater levels continue to drop because of overdraft.  More simply put, we are pulling water out quicker than it can re-fill.  And it doesn’t help that a large percentage of our urban areas are paved and impermeable.  Providing space to allow water to infiltrate is essential in replenishing this dwindling resource.

Creates valuable habitat for wildlife:  Wildlife, like humans, flock to water.  Small depressions or basins that hold water and moisture for a few days or weeks after a rain event are critical to the long-term success of wildlife.  
bioswale with native grass, rush, and sedge

A vegetated swale, or "bioswale".

Ways to Store Rain in the Landscape

1.  Install heavy layer of mulch:  Mulch, tree trimmings, or other organic forms of soil cover create a matrix in which moisture can be absorbed.  Mulching bare soil will also reduce the chance that valuable topsoil could be washed away in heavy downpours.

2.  Plant succulents:  Here is an easy one!  Succulents get through the dry season because they store vast amounts of moisture in their stalks and leaves.  Rather than needing moisture in the soil during the dry season, succulents rely on the water they have stored.  Sound familiar?

3.  Plant trees:  Mature trees hold an enormous volume of water-from the trunk to the leaves.  As such, they are very efficient at moving moisture from the soil and transporting it throughout their structure.  The canopy of mature trees also hold moisture and can act as a large drip emitter slowly releasing its bounty over hours and days past the end of a rain event.

4.  Create bio-swales:  Bio-swales are simple, vegetated linear depressions that slow run-off, reduce sediment transportation, and rely on plant material and soil composition to absorb, cleanse impurities, and slowly release run-off into the watershed.

5.  Reduce amount of hardscape areas and replace with permeable materials:  Give rainwater every chance it has to be absorbed by eliminating impermeable surfaces such concrete and replace with gravel or mulch.  Keep in mind:  your lawn may also be an impermeable surface if it has not been properly maintained.  A lawn cut high and well-aerated will provide tremendous absorbtion.

6.  Install rain-barrels or cisterns:  Save what mother nature gives you.  Pipe your downspouts into storage devices that allow you to access the water when you need it in the dry season.

7.  Install dry wells:  A dry well can be an underground structure or gravel-filled pit that is used to slowly dissipate rain water.  If the soil becomes saturated, even the best designed landscapes will produce run-off.  Dry wells provide an underground cavity to hold a large volume of water and allow the water a place to slowly percolate (usually over a number of days) deep into soil.  

8.  Create retention or detention basins:  The main difference between these two storm water components is that retention basis RE-tain the water permanently and detention basins DE-lay the water and release it slowly over time to downstream conveyances.  These basins can be any size but are generally large in order to hold a huge volume of water.

9.  Create infiltration basins:  An infiltration basin differs from the above basins in that it can be any size but its sole purpose is to hold water at the surface in order to allow for percolation into the soil and aquifer below.  Usually these basins have a specific base filled with porous soil or aggregate to facilitate more efficient percolation.

When you garden, consider implementing some above low tech and low cost improvements.  The ultimate aim should be to reduce or eliminate run-off from your property.