Sat 17 Jan 2009
To: Mr. Hartman with GPD Engineering
From: Terry Casey
cc: David Mackey, Doug Roberts
Thanks for your call today. Glad to learn that the City is doing an in-depth, independent evaluation of the new culvert on Overbrook Drive between Cooke Rd. and Lenappe. As I understand, your work will look at the effectiveness of the recent fixes, actual water flow history and needs, future maintenance questions/costs, etc.
At your request, attached are five of the pictures I took on June 26, 2008, including the up to 30″ of pavement “undermining” that happened during that three-inch rainfall incident that had closed this new construction project. Since that incident, the City did have a firm do work to clean up some of the build-up under the bridge and upstream.
The key question, of course, is whether that is a real, long-term solution or just a temporary “Band-Aid”.
Let me know if you have any added questions.
Many in the area will look forward to seeing the results of your report and the options being considered for long-term maintenance.
I have more pictures and at higher resolutions, if needed. Let me know any other background/history needs on this project.
A few email responses:
Kenn Cahill says, 1/16/09
Terry, I agree with you that cleaning out under the bridge is short term damage control. The stream ultimately re-establishes its “bed”.
Terry Casey says, 1/16/09
It’s good that the City is doing this study . . . and by an independent firm from Akron. I’m checking with some key sources on this firm who have worked with them up in Summit County.
You’re 100% correct on nature and the tendacy for the “re-bedding” of the creek over time. You can clean it as they did this past summer, but it fills up again.
JUNE 26 FLOODING: The engineer was asking about flooding on the morning of June 26. It was a three inch rainfall and happened at night. My sense was that most of the big stuff and problem was on the new bridge, not on the other three bridges to the west along Overbrook Drive. Any re-call you have with the bridge below your house on that am? Am copying to some of the neighbors on their re-call.
Bill Burns says, 1/16/09:
From Kip Patterson dated 1/16/09:
I disagree in part with Ken’s comments as follows:
Moving water picks up sediment and larger material in an amount that is largely governed by the speed of the current. It deposits those materials when something causes the current to slow down. You will recall that the stream bed at the bridge site showed little or no sediment, in fact the billiard-table smoothness and cleanliness of the black shell was a big part of its attractiveness.
The problem started with a simple engineering error. The hydraulic calculations were based upon a rectangular bridge channel, 24 x 4, for an area under the bridge of 96 square feet. The bridge as designed and constructed used pre-cast arch sections. Without detail drawings of the arches, we can only estimate the actual flow area. I bet it is the area of 64 square feet, or two-thirds of what it should have been. Once the flow reached the top of the arch, it slowed down and dumped its contents above, under, and below the bridge.
We, especially the city, should be happy about this fortuitous error. I looked at the culvert under High street after the flood. It was immaculately free of debris, but an examination of trees and shrubs in the area showed that the water came within a few inches of filling the culvert. If the upstream culvert had not served as a detention structure the overtopping would have been at High street, and the first floor of 4100 High, built directly over the culvert, would be lying in the middle of High Street.
What is needed is upstream detention in areas before the stream is exposed to debris. Unfortunately, there has been a great deal of construction upstream. In particular, the city constructed a new storm sewer without detention, contrary to their own rules.
Kip Patterson, PE (ret)