Flooding Streets to Control Storm Water 6

[TBCEng07]

Our City fathers have come up with the idea of flooding the streets to help eleviate basement flooding. The area of concern has combined storm and sanitary sewers, so when the sewer becomes overloaded it floods into the adjacent homes.

I am sure that I am going to be asked to study the feasibility of this effort.

Has anyone else had any experience or guidance for me?

I admit this approach sounds counter-intuitive. I mean the purpose of storm sewers is to convey water from the streets. I think the real answer is to install new sanitary sewers and separate the systems.

 

[bltseattle]

Interesting subject. It is a good thing to think outside the box. Here are some ideas, some rehashed from the above:

A street storage system would have to operate by detaining the street runoff before it is combined with the sewage.
There is an EPA factsheet at:

http://www.epa.gov/watertrain/smartgrowth/resources/resident.htm

The EPA example is (a) a residential street, not major arterial, and (b) in a sag condition.

I don't think this idea is practical on a continuous grade or on a higher use street, but could be used in certain instances to make "self mitigating" streets. I think street edge "rain gardens" ala Seattle "SEA street" is a preferable system because you can maintain traffic flow and get more storage in a sunken landscape than the 6-inch max you would be able to store in the sag of a typical curbed street.

For two 12-ft lanes with typical 6-inch curbs, at 2% cross-slope and crowned in the center, your average storage depth would be about 4.4 inches, which is not too shabby so long as there is not much run-on from adjacent surfaces. Maybe that's why the increased the curb height in Skokie and Wilmette.

I assume this would work by putting orifices/flow regulators at catch basin outlets (NOT by allowing combined sewage to back up, which as noted above would never be allowed and would be a huge public health hazard). Who would be responsible for maintaining/cleaning these flow restrictors?

I'd provide an overflow grate (or two or three) outside the roadway "prism" because this type of system will tend to overflow the curbs and flood adjacent properties when storms exceed the volume or intensity of the design storm used to size the orifice/restrictor devices.

Maybe your City founding fathers should consider some incentives for private property owners to implement "source controls" such a green roofs or porous pavement. I've heard that Minneapolis recently restructured stormwater utility fees so that those contributing the most runoff pay the highest stormwater fees, and fees could be reduced by implementing stormwater control measures. Previously, their stormwater fees were linked to water bills and usage, so a single family residence was paying a higher stormwater fee than a pay-parking lot that did not use water at all.

That said, our research has shown that as much as 40% of all urban land is public street and right-of-way, so for most combined sewerage areas, controlling discharges from private properties is only part of the solution, and managing street and sidewalk runoff may have to be addressed sooner or later, as would be done by using street storage.

I would prefer a big underground detention tank to retrofit a street if I was an agency, however, because it would require less maintenance overall (one-stop shopping vs a multitude of flow restrictors at every inlet). Maintenance could be one of the ultimate factors for deciding that street storage is not a practicable solution.

 

[RWF7437]

From all of the previous responses I'd be willing to bet this scheme cannot work, cannot be shown to work, cannot be approved by any State or Federal agency having jurisdiction; including the EPA, FEMA, State Health Agency, State Environmental Agency, State Highway Department and others too numerous to list.

And your town probably can't afford it. This is not just out of the box but it is out of somewhere. If you actually proceed with this be prepared to talk to Lawyers the rest of your life.

 

[civilperson]

The practice of using curb deep storm water flows in the street is normal for storm events greater than the pipe system can handle. The combined sewer and storm systems are prohibited and existing combined systems are require to split the two types of flows under threat of fines from EPA.