Bioswale, Vegetated Swale, or glorified drainage ditch?

Vegetated Swale or Bioswale
As a landscape company, we install a number of different elements in order to create a fantastic landscape. Some of the requests don't come from the designer or even the client but from the city in which we are working. Recently, we were requested to install a Bioswale or Vegetated Swale into which all the rooftop rain drainage would be directed via gutters, drains and drainage pipes.
The City of Encinitas was very specific about this item, its incorporation into the landscape, and its construction. I personally had to do some research for our client to see why this Bioswale was so important.
Bioswales were developed in the States of Washington and Oregon for a specific purpose: to clean contaminated run-off from parking lots and industrial areas so that once the water and pollutants percolate through the swale, the subsequent run-off is 'clean' to continue down to the water table.


I found it strange then that we would need to build something of this magnitude on a private residential property with no contaminated run-off (no lawn that may have excess fertilization, no contaminated industrial water, no chlorine because the pool being installed is salt-water).
Bioswale Diagram (not by City of Encinitas) 
But because the owner of the property mentioned to the soils engineer that she would like to retain her rooftop rain water and use it in the garden to water some trees and plants, this is what was developed and put onto the plan. With plenty of arguing with the planning department about the Bioswales (2 of them) being overkill, our client really only wanted to drain the water over to the tree and planted areas, and a couple of perforated pipes would be all that was necessary for what the owner wanted to do. The city finally concluded that the Bioswale had to stay on the plan and to be installed and approved before the pool could be finalized. So, we built them. 


Trench
First we had to trench out a 2 foot drainage ditch with a 4" lip for the swale to be 4 feet wide then we ran drainage into it from all the gutter downspouts into a perforated pipe that runs the length of the swale.
 We then filled it with 3/4" gravel and then 3/8" gravel and topped it with "Engineered" Bioswale Soil that is meant to never compact and to drain run-off and rain water through the swale without filling the gravel with silt. It is basically a giant multi-substrate filter.
Gravel Added
Engineered soil and plantings
The Bioswales do nothing to retain water for the trees and plantings that our client originally wanted this rain water to help irrigate. And, ironically, in order to keep the swale plantings alive through the summer months, we will have to irrigate - does anyone think that seem a little strange for what this landscape element is supposed to do? But really, who am I to argue with the progressive nature of a Southern California city? I'm just a landscape contractor, people in offices are the ones who decide what will or will not work for the given drainage situation.

Comments

Anonymous said…
I hear you. It is so pointless and frustrating, not to mention expensive. We are going through this same issue on a small residential lot in Santa Barbara. It borders on ridiculous in our situation, but they are demanding it regardless of it being needed. I can see it being pertinent in many situations, but on a small residential lot with no drainage issues to begin with it costs a LOT and does basically nothing. I came to ýour site in the hopes of finding the best succulents to use on this bioswale that must run down our driveway.
April 11, 2013 at 7:38 PM
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