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June 3, 2013 / Brandon

Parking Lot, Swales, and Drainage Driveability

Parking Lot, Swales, and Drainage Driveability

I like to drive around and look at how different designs work on different projects. Driving a parking lot designed by someone else can give great incite to what we can possibly change or do better on our Civil Engineering designs than what is already out there.

I am not sure who the original designer was for this particular parking lot located in the City of Pasadena on Arroyo, and we had nothing to do with this project. While waiting to get some Hawaiin Food from L & L Hawaiin Barbecue, I decided to walk around the parking lot taking notice of where the swales were routed and take some pictures that were more interesting to what I was looking for. We at B+W Engineering like to design a parking lot with driveability in mind. That means not having a low car scraping anything or bumps and humps all over the place making the car’s suspension work overtime. We do so much design for custom houses that exotic cars always come into mind. And since we live in Southern California, with its car culture, these exotics most likely will travel into any random business. Driveability also means that walking around the parking lot should be easy to do.

The first picture shows the swale that leads from the trashcan area which is one of the highpoints on the property. This is pretty typical, though I would prefer to slope the whole area towards where this swale is routing to. That cuts down on building cost and doesn’t need to be there. What happens over time is that where the asphalt meets the concrete swale, over time starts to get damaged, which is happening here. Nothing wrong with this at all, but there is extra maintenance or just can look ugly faster. And like I mentioned more expensive to build this portion of concrete swale.

The next picture shows something that I really like. The way the swale is coming from another highpoint on the lot. As the water travels from the back of the property, the water goes into the parking spaces that have a swale running through where the car is parked. To outlet from that area the swale goes right through the curb and landscaping. This helps keep the site lower which means less fill in most cases. Otherwise the swale would have most likely been placed between the parking stalls and the back of property line adding more linear feet of swale. So less earthwork fill and less swale means cheaper cost to build. This isn’t always possible to implement depending on the site layout, but works very well on this particular site.

This picture shows how the swale from the trashcan area connects with the swale from the parking stalls. As I mentioned the swale coming from the trashcan area could have been eliminated to have all of the water flow graded directly at the curbface that is painted red. On a plan this looks more elegant. But driveability is more key to me, and this means cars have to cross the swale. Just a little touch we like to do is have as little crossing of cars over the swale whenever possible. Once again nothing wrong with this design as it works well.

Here we have a picture of the other lower point of the parking stalls against the front of the property along Arroyo. The drainage concept for this project was to put a swale at the front of the parking stalls which works well. This also can give a natural place for a car to rest if the parking brake isn’t set and the car rolls forward. This also cuts down on that thing I mentioned above about crossing swales while driving through a parking lot. I like this type of design when it can be implemented.

This is where all of the drainage gets tied together from the entire site to outlet to the street. I do not particularly like this as driving feels odd over this as someone is either exiting or entering the property. The good thing is that the swales aren’t deep which isn’t as bad as some other parking lots I have driven on. I drive a Honda S2000, a small 2 seater roadster, which I can feel some of the imperfections more than say an SUV. Always in the back of my mind I am thinking can a Ferrari, Lamborghini or other exotic drive what we design easily?

This picture shows the end of the drainage pattern for the parking lot. I don’t see this too often and with Pasadena’s newer more strict SUSMP requirements this can’t be built anymore. I don’t see any filter devices for the stormwater from the asphalt whatsoever. So most of the property is draining dirty water into the street which goes to the storm drain system directly into the ocean. Filtering the water using fossil filters is a minimum standard before any water exits a commercial lot. Newer codes are requiring tanks that take the first 3/4″ storm and infiltrate the ground underneath the parking lot to help from over utilizing the storm drain system, and also recharging the earth underneath the property.

The other part that I do not like about this design is the trip hazard this produces. Not only would this be easy to fall into, but worse is that this is sitting up against the sidewalk and almost feels like its part of the sidewalk. Also looking from the picture debris can easily clog this outlet.

The pictures to the left shows how we normally place a trench drain along the parking entrance width and pipe the trench drain out with a rectangular pipe through the curbface. Inside the trench drain is the fossil filter cleaning the stormwater. If this was to clog or overflow the stormwater will take the natural path right over the driveway preventing the property from flooding or pooling up anywhere.

I like to drive around to see what we can pick and choose from existing projects to use on our plans. I also like to drive around the lot to see how a car feels through the property. This ends up helping us come up with better designs, especially with the newer SUSMP/LID requirements that make some designs very hard to work with what we are trying to accomplish. Our Civil Engineered Grading Plans still look elegant on paper but the better part is that the finished design can be that much better for everyone visiting the location. Stormwater drainage is very important and there is a lot of thought put into what we think is the best design for our clients.

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