In nature, water is usually given time to slowly absorb into the ground, occasional extreme rainfall can overwhelm the ground causing flooding but nature has developed ways to handle the water. Urban environments containing massive amounts of concrete eliminate the natural watershed, but all of this water has to go somewhere. Any opportunity to use the run-off in the city should be utilized, it’s just common sense… But just incase you are still not convinced…
Excessive urban run-off picks up all of the pollution laying on the ground and fast tracks it past the natural systems of filtration, centralizes it, and dumps it straight into our rivers, streams and lakes. All of the oil and gas that is spilled on our roadways is flushed down the storm sewers, these sewers drain directly into our rivers, and our rivers empty right into the ocean. Normally rainwater has a chance to be absorbed into the ground, the simple act of that water percolating through our soil is what filters the pollutants out… Once they are filtered out, phytoremediation (land remediation using plants) processes can begin and eventually nature would handle or compensate for the load.
When we pave every surface in site, water does not have a chance to be filtered. The theory behind a rain garden is simple, create a place for the water to collect to give it the time required to be properly absorbed into the ground regardless of how long it takes. The concept is simple in that it is just a hole in the ground, as with anything there are grades and scales that need to be considered. Amount of water, soil type, plant types and worst case scenario are just a few things to think about, every site will be different.
Rain gardens are often mistaken as a solution to flooding, although they could alleviate the frequency or intensity of a flood, they will not stop them. Storm water management plans always have a limit to how much water they can handle, nature likes to occasionally show us how limitless she can be. You can only humanly design a rain garden to handle so much water, I have seen them not only flood… but fill to the brim with rocks and mud… on top of $500 in brand new plants. All of the planning in the world couldn’t have prepared us for the 4″ of rainwater we got that morning, I’m going to stress again that rain gardens DO NOT stop floods! I worry people will want to install rain gardens as a solution to floods, only to be discouraged when it fails.
Rain garden design starts with identifying the need for one, and finding the most logical location. Not every site I visit needs a rain garden, rain gardens are not a requirement of permaculture by any means. They are a great solution to design problems that include the shedding of water, a last resort to water collection for other purposes. Urban environments pose an interesting problem due to the pavement to soil ratio favoring pavement, all urban rooftops drain to the same pipes the street runoff drains to… that’s a lot of water! Simply running those gutters to a hole in the ground filled with rocks would alleviate some of the strain, rain gardens just make that concept look nice.
Location is really just a logical decision, look for a place that water regularly pools, usually a depression in the ground or constant wet spot. The location in my experience, has been chosen for me, whether it’s man-made or natural, you will just know that it is the “logical” spot for it. Sloped properties that funnel to a central point also logically benefit from rain gardens, several rain gardens built down a dry valley could give most of the flood water that would otherwise run to the bottom of the property a chance to be absorbed into the ground. Rain gardens built-in a location like this would help control erosion as well, trees established in the “dam” side of the garden would secure it for years. On a larger scale these would be lakes or ponds, just dry “most of the time” and adapted for home gardens.
Rain gardens don’t have to be about necessity, they are also a great way to handle the run-off from your gutters… I need to mention that this will not stop flooding in general, but it might stop your basement from flooding. A medium-sized rain garden properly placed away from your house, could easily handle most rain loads off your roof.
1 inch of rain, on a 1000 square foot roof will produce 600 gallons of water… Think about that for a couple of seconds… I’ll wait… ~~Modern rain barrels are equipped with overflow valves that when full, could flow into a rain garden. Honestly… Most rain barrels I come in contact with are only 60 gallons, have never been used before, and they have usually been full for years… A friend had one installed because they were told it would stop water from leaking into their basement, it worked for a week till the small barrel filled up… They didn’t garden and had no need for the extra water, it filled and the overflow was not set up properly… Sadly this person will not install another rain barrel ever, they would have been better off directing the downspout 5 or 6 feet into the grass… And the rain barrel wasn’t cheap… $150 I think…
Rain gardens can be one of the great features in your landscape, creative colors or river rocks can set them apart. If you don’t want a depression in your yard you can fill it to the top with rocks, the volume will be different but essentially it’s the same thing. If you can dig a hole, $150 can buy a lot of plants, native plants are prefered for their drought tolerance… after all, watering wouldn’t be rain! Trees require mentioning here, willows can absorb enormous amounts of water, so much that they have been known to break through drain pipes with their roots to get access to it.
Rain gardens will not solve all of our watershed problems, though they will alleviate them considerably. Whether used as a solution for erosion, or as a functional focal point in your landscape, rain gardens are here to stay! Although they are currently popular, they have been around for thousands of years in one form or another. I consider rain garden plants to be a post on its own, I guess you will just have to wait for me to get around to typing it up…
whiskeys worth drinking, but waters worth fighting for – chriscondello
The great Whitney Avenue 4th of July 2011 flood, I told the kids sewers are not garbage cans… Did they listen? Obviously not… These sewers are filled to the brim and flood at least once a year! Rain gardens won’t stop this but could lighten the overall load considerably.
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