10 May 2010

Permeable Pavements

I've been noticing the City's Engineering Department has initiated a project to install water permeable pavements in some locations. This is a fantastic development.

Solidly paved surfaces treat rainwater as a waste product. Rain is typically channeled and piped away as quickly as possible. This is a problem because the vegetation (street trees mostly) needs that water.

Also, all that channeled rainwater overwhelms our combined sewer system during heavy rains. Any water diverted from the storm pipes save the City headaches.

So I noticed that last week during a heavy rain, that no water was being channeled down Comer Alley. Comer Alley is a one-block alley that parallels Race Street and runs between 14th and 15th. It was re-built last year as part of the OTR Community Housing Project "City Home". It was rebuilt to make it easier to use so that vehicles could access new rear garages. Before, the alley was only eight feet wide between granite curbs, and this made it very tight in which to drive a car.

The Alley bricks were removed, and a permeable gravel base was installed. Then the old bricks were re-installed level with the granite curbs. When the bricks were reinstalled, slight gaps were left between the bricks and filled with gravel. These joints absorb all the water and direct it into the ground. It is a beautiful solution to several problems.

Here is a picture of nearby Osborne Alley, half-done:


See here for some during construction photos of the alley.

I also noticed that a similar effort was made at University of Cincinnati, near trees. Notice that here, the pavers are laid in a different pattern above the tree roots, allowing water to enter the ground:

UPDATE: Here is a great article about permeable alley pavements in Chicago


Jeffrey Jakucyk said...
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Jeffrey Jakucyk said...

Rebuilding the alleys like that is so indescribably awesome I can barely believe we're seeing something like that here. It's great also to see how the city has embraced reusing the old granite curb stones in recent streetscaping and rehab projects such as Woodburn Avenue, Oakley Square, and St. Gregory Street.

This approach is an interesting way to combat the problem of the alleys being so narrow, but I do wonder if it won't cause problems in the future. The brick surface still has a crown to it, so if the gravel gets saturated, then water is still going to run to the sides, and it could pool in places that could cause a hazard. This would be especially problematic in winter if ice forms. Many alleys in other cities (even Covington and Newport) are pitched in towards the middle, especially ones that don't have curbs. I wonder why they didn't do that here.

Many of the alleys do have drains at intersections, so I wonder if they've planned it such that runoff would flow through the gravel under the bricks to the drains rather than on the surface. It would be interesting to see how this performs after years of use has let small particles of grit, dirt, and plant detritus to clog up the gravel.

CityKin said...

Yes, it is an experiment, so it will be interesting to see how it works. There are still drains at the ends, where the alley meets the street. I never thought about the crown, but it kinda makes sense to try low in the center instead of high in the center.

catherine said...

I love people that love alleys!