Oakland county MI has had some major floods recently, e.g. August 2014. That flood sent raw sewage 1 1/2 feet into people’s basements and buried cars past their roofs on the main highways of the county (Hwy 696 is shown below). We also sent near-raw sewage into Lake St. Clair, just upstream of the water intake. This is the effect of county-wide wealth above ground, and third word drainage below; 8 mile road in the west of the county regularly floods, and our beaches are closed every other week in the summer.
Fishermen report giant, black mats of sewage floating in the lake to Detroit, and the metro beaches are closed in the summer as often as not. These are symptoms of bad plumbing and they need to be addressed. I have a few engineering solutions. Some that do a lot and cost less; others that do more and cost more. They deserve consideration.
The best long-term solution is to separate the storm from the sanitary sewage. Not that it should be done all at once (that would be costly and disruptive), but it’s a direction we should be heading in. I’ve suggested to the county executive that we use the expansion of I-75 as an opportunity to lay a large storm-water drain that could serve nearly the entire county. This is a cheap and basic building block, and a once in a generation opportunity (he agreed).
We will want to have storm retention on the pipes that feed this drain. This allows one to slow the flow going the rivers. Without retention, the rivers become ‘flashy’ and we’ll have erosion every time there is a big rain. Cheap retention can be done with weirs, with small wetlands, or by French drains in places were space is more limited. French drains are basically ditches filled with rock, typically 3/4″ rock, often covered by a parking area, walkway or bicycle lane. There is a perforated pipe at the bottom, sized so that the flow out will be acceptable. The ditch provides absorption into the ground, and the cost is low, about $100/ lineal foot, or 25¢/gallon. This is about 50 times cheaper than the tunnel cistern being built under Middlebelt road. In a tunnel cistern, the storage is in the tunnel tube. There is no absorption or remediation, and the cost is more like $13/gallon.
Some designs of French drains include wood chips and loam. This further improves absorption and bio-remediation, an important consideration for dealing with mall parking lots – places where you can expect the storm water runoff to mix with spilled food, motor oil, and bird poop. Some designers like to grow water-tolerant trees or grasses above a French drain (I prefer trees). When the area is indented below grade and seeded with grasses, it’s called a rain garden. These can become animal habitats, a welcome thing in some areas, not so welcome in others. Some rain gardens are attractive, some not so much. Most designs provide significant absorption into the ground and into the foliage, but they have to be designed right.
Another option, cheaper than a French drain, is a ditch. They cost less than a French drain, only about $10/lineal foot, 3¢/gallon of storage. Ditches are used in rural areas where there isn’t much traffic and land values are low. They tend to be rather ugly, to my eyes. They’re often highway safety hazards, too. A car that runs off into the ditch can kill the driver. A driver is much more likely to survive hitting some small trees growing above a French drain. Where ditch drains are used, I’d like to place a permeable curb and small gravity dams to increase the residence time and provide some oxygen. Oxygen is a key element to sewage treatment. The dams can allow ditch retention to provide bio-treatment, e.g. to bird poop and spilled motor oil. Oxygen in the water is the difference between a living river with fish, and a smelly sewer that can not support life.
One final issue is de-bottlenecking. Every system has a bottleneck, a slowest part that limits the amount of rain flow we can get rid of before it backs up in our homes. You want to find the slow spots and expand them in a responsible way. There is an art to finding these spots and to choosing a fix that doesn’t cause problems elsewhere. That’s why you want an engineer as water commissioner.
For more about my approach to engineering (or science), or roads, or education, or statistics, or anything else, you can check out my campaign Facebook page, facebook.com/electbuxbaum, or my blog with 250 entries. If you like what you see and want to volunteer to my campaign, or contribute, go to www.electbuxbaum.com/volunteer, or write a check to “the Committee to Elect Robert Buxbaum,” 12851 Capital St., Oak Park MI, 48237. For nearly any amount, you’ll get a campaign pin, my thanks, and my blessing.
Robert Buxbaum, May 20, 2016. My blessing does not require an action or donation. You have to do something to get my thanks, though.