Its always hard to catch a recently constructed project during the rare storms in Southern California. Recently, I was able to catch stormwater running through a bioswale.
This is what a bioswale looks like. A bioswale is used for Low Impact Development (LID) to pick up the stormwater from the entire site where new construction occurs. The grassy swale is designed to collect and filter the first 3/4 inch storm. During any small storm, all stormwater will stay on site which will help keep the storm drains from pushing more water to the ocean. A new Church was being built so quite a bit of water will be flowing through this swale.
The above picture shows that all water will make its way to the swale sitting near the sidewalk. To help prevent infiltration from going towards the street, the sidewalk side is lined with plastic. If we lined the entire swale with plastic we would need a perforated pipe to outlet somewhere to the street. There was not enough fall to do this with gravity so we chose to line only one side. Also this allows the water to percolate through the soil giving much more chance to capture even more stormwater on site. The builder was very happy at how well this worked, so that in turn made me happy hearing that.
I am a stickler for trying to follow the rules as close as we can and we had a problem that the bioswale was not the required 100' minimum length. The City allowed us to chop this up with a concrete pathway. I came up with a way to drain over the path, but the builder decided to put a small pipe to get from one side of the other. My way was cheaper, but I prefer their method, and both would work.
The catch basin against the property line on our plans always gets questioned. I put this hear to connect drains to and also have a way to connect the drainage pipes going from the property under the sidewalk through the curb face to the street. While its not always visible why these are here, its all under ground. Technically the grate should be picking up the overflow from the bioswale, but the lid grate was built slightly higher than the existing ground. Not a problem as we can soak a bit more of the front lawn before the storm water outlets to the street. I look at that as a win win when trying to keep as much stormwater on site. The grass and topsoil will also act as a natural filter. Being a Church I also doubt that this will clog with trash, so the whole system does not need a backup, though the catch basin can also act as a backup. If the water from above connecting to the catch basin through a pipe system clogs then the water will pop out above or possibly pop out of the lowest point. Like I said there is a bit more going on than what this looks like.
Onto seeing the parkway drain coming out of the sidewalk during a storm. Notice there is no water coming off the site. We are collecting close to an acre of water and not a drop in the street.
Like the builder, I was also impressed at how well this worked so I need an angle shot to show this better. We rarely have enough room on a site to put these in, but this is always the first thing I try to design in. We will be placing another bioswale in not too far from the Church, down the street in Montrose.
To get a better idea of how this works I took a couple of quick videos. The downspouts from the building and upper walking areas outlet at the start of the bioswale.
From there the storm water makes its way towards the end of the grassy swale to the catch basin. From the catch basin a rectangle parkway drain outlets the storm water to the street. In this example no water flows off site. As you can see how much water is flowing down the street gutter, we help just a little.
Eventually all new construction will be going this direction and the only water in the street will be strictly from the street drainage or very large storms. I did hear in the distant future that 100% of onsite stormwater will have to be converted to potable water. But I doubt that will happen over the next 40 years. We are talking massive pumps and complex filters to make that work. Where what we have today is very simple and easy to maintain.