A Lesson I’ve Learned Several Times

Underside of Bridge

When you’re working on a highway design project, you receive information from multiple sources, throughout the life of the project. It’s important to verify the information you receive so that you are not subject to GIGO1. An example of this is the survey data that you get before you can start any of your design work. The survey crews will go out and locate where the roadway is, the edges of pavement, the location of each utility pole and fence and bush and drainage pipe. All the above-ground features will be found and located to (hopefully) a very tight tolerance. It is usual to take the survey data, put it on the plan sheets, and then walk the project to confirm that A) everything on the survey is located correctly and B) everything in the field is on the survey. Typical problems that arise and have to be corrected are drainage pipes that aren’t found or manholes that aren’t marked. That is one example of field verifying information.

Another is utility information. Utilities include water lines and gas lines and electrical power cables etc. These are fairly easy when they’re strung on overhead utility poles: while I might not know who’s lines are strung on the poles precisely2 I at least can see them, and I know where the poles are. I will know if I have to move one of those poles and that some Generic Utility Company will have to come out and restring their lines.

It gets more complicated with underground utilities. Sure, there are manholes that can be found that identify point-to-point where some things are, but generally we’re dependent on Utility Companies to tell us where the various water lines and gas lines and underground power lines are. There are methods3 for verifying the information received from the Utility Companies but it’s much more difficult.

However, there are times when it’s easy. For example, if a utility crosses a bridge, it has to do so by hanging from the deck or a beam. These are easily found and verified by walking under the bridge and looking up.

Just yesterday I discovered that some utilities that we’d been working on feverishly did not actually exist.

They may be somewhere, but they’re definitely not where we thought they were, i.e. they’re not hanging off the bridge we are working on. This makes life much easier, but it also means we did a lot of work for nothing.

So, once again, always verify your information in the field, to the extent possible. I hate learning lessons I already know.

  1. Computer Science term: Garbage In, Garbage Out []
  2. could be power, or cable tv, or telephone, or fiber optic []
  3. in Georgia this is called Subsurface Utility Engineering and has four different “levels” of quality. Qual D is just a records search. Qual C is a site survey as I’ve described above. Qual B is when an underground utility is located via a magnetic cable finder or other method and then the location of that pipe or cable is surveyed on the surface. This is what you see when you see yellow or red or blue paint on the ground marking utilities. Qual A, the best level, is when a hole is vacuumed in the ground and the actual cable, pipe or whatever is physically surveyed for exact X, Y, Z coordinates []
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A Post about Drainage – In Which I Opine with No Real Knowledge about the Legalities

Last weekend, I attended Momocon at Georgia Tech, primarily to see The Extraordinary Contraptions play.1 I went down a bit early from the start time so I could wander around that part of Midtown Atlanta and just see what could be seen (and take pictures).

I happened across this particular situation in an alley.
Drainage 1

I noticed the eroded watercourse as I walked over it and looked to see where it was coming from. I followed the water back to the hole in the concrete wall shown on the top left of the image. You can see a closeup of the hole in the following image.

Drainage 2

You’ll notice that this hole was not created at the time the wall was constructed. You can see rebar within the hole and it’s a rough-hewn rectangle. It’s obvious that someone came along and knocked it out to allow for water to leave the parking lot and drain away. There has been significant erosion underneath the hole. You can see a line on the wall where the level of ground used to be. This has all been caused by the drainage from the parking lot.

Here’s a picture of the parking lot.

Drainage 3

You can see, in the center of this image where some debris is against the wall, the low point in the parking lot where the hole was knocked out of the wall to allow water to escape. It’s hard to tell elevations from this picture but when I was standing there, it was obvious that without some sort of drain inlet, the parking lot would develop a very deep pond until the water could seep through the cracks in the asphalt.

Drainage 4

This image shows where the water eventually ends up going. It drains across the alley and into a drop inlet where I assume it meanders its way through the Atlanta stormwater system to the Chattahoochee.2

Questions that immediately jumped to mind when I saw this were:

  • What are the legalities of the owner of the parking lot arbitrarily knocking a hole into the wall (which is owned and maintained, I’m sure, by the parking lot)? Should a permit have been obtained? Is there anything actually unlawful about this situation?
  • Who owns the swath of land between that wall and the alley? If it’s the owner of the lot, then I don’t think there’s anything going on here that is wrong, per se, although the condition of the eroded drainage course isn’t something that qualifies as “good”.
  • What are the permit responsibilities for property owners within the City of Atlanta for maintaining the drainage of their properties? Is the property owner responsible for the damage that the water is causing to the alley or is that the city’s responsibility?

Now, if I were the City, I’d want to make it the property owner’s responsibility to address the problems I see in these images. There’s obviously too much water coming through that drainage hole to be handled by a grass or dirt drainage course. The erosion demonstrates that. There should be a properly piped outlet or paved ditch that takes the water to the stormwater drainage3. Unfortunately for the property owner, I can tell that there would have to be some significant pipe installation to address the drainage here. You couldn’t just pave a ditch from the hole to the drop inlet because that would cross the alley, impeding traffic. The most proper way would be to take the water into a pipe, which is installed underground and connected to the box the drop inlet is attached to.

If I were the property owner, I’d want the city to handle and maintain the drainage because that’s an expensive proposition. From my own experience4 I’d say that if this became an issue, the property owner would be stuck with the cost of addressing this problem. I think there are plenty of city ordinances and regulations that would place the onus on the property owner.

But would such a condition arise unless someone made an issue? Probably not. I mean, the only reason I happened to be talking about this is because I was walking down the alley and noticed it. The drop inlet to which the water was draining seemed to be functioning fairly well (although a lot of that sand-colored stone you see in the image was piled up on leaves and other debris, blocking half the grate). So long as the amount of water being handled by the inlet exceeds the amount coming off the parking lot and alley, no problems will occur to the other property owners adjacent to this drainage feature, notably the apartments and houses on the left side of the image.

I took a close look at that drop inlet to see if it had been overwhelmed during our last rain incident and it seemed like no problems had occurred. However, the inlet is in a slight declivity, which is the low point of the alley, but not the low point of the entire area. There is a small berm, shown against the rock wall in the mid-bottom-left of the image above. The other side of that berm is the back yard of a private residence which slopes toward the house, and not toward the alley. If enough water comes to that drop inlet to overwhelm its capacity (and that’s easy to do if it has a clogged grate) then the majority of that water could spill over the berm and into that yard.

The clever or close-reading among you will immediately object to the inference I’m drawing here: “But the amount of water going to that drop inlet is independent of whether that parking lot has a properly designed outlet!”

This is true. However, let’s postulate the following: The homeowner was flooded because the drop inlet couldn’t handle the rainfall because it was blocked. Who’s fault is that? The city’s because it didn’t properly maintain the inlet or the adjacent parking lot for causing a condition that drove significant amounts of material into the inlet?

That, of course, would be something for the courts to decide.

It may be that these questions have already been answered. I’m not experienced with City permitting and drainage/erosion/stormwater issues. That’s more of site engineer’s bailiwick than an transportation engineer’s. These are the kinds of things I think about as I move around our built areas5.

  1. Momocon is an Anime convention and what I know about Anime can be fit onto a 3×5 index card []
  2. You can also see an attractive woman who is suffering from a charisma modifier of -5 because she’s smoking. Why do people smoke anymore? I don’t get it! It’s expensive, a lot of people like me find it a huge turn off, and it’s being aggressively shoved out the door and into the street. Oh, and it will kill you []
  3. This feature is what we call the difference between sheet flow and concentrated flow. Sheet flow is what you get from water draining over ground without being concentrated by natural or built features. Think a hillside or a smooth parking lot. Concentrated flow is just that, where water is channeled into a course, such as a ditch or a pipe and becomes concentrated. Concentrated flow can be very destructive if not properly handled []
  4. very limited. I haven’t handled much in the way of local jurisdictional permitting and nothing to do with site plans and drainage []
  5. Yes, I’m a geek []
Posted in government, legal, opinion | 4 Comments

Better Titled "Hemingway's Takes on Classic Bar Jokes"


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Episode 37 – Georgia Transportation Funding

Topics: Transportation Funding


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Episode 36 – HAWK Pedestrian Beacons

Topics: HAWK Pedestrian Beacons

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I Learn my Job Every Day (Cross Post)

This is Cross Posted from the Evil Eyebrow. Please leave comments over there
2010-10-17_IMG_2436

If you had asked me yesterday, “Bill, can you prevent pedestrians from crossing a bridge during construction?” my answer would have been “Sure.” And I would have been wrong wrong wrong:

From the 2009 Manual on Uniform Traffic Control Devices (MUTCD):

04. If the TTC [Temporary Traffic Control] zone affects the movement of pedestrians, adequate pedestrian access and walkways shall be provided. If the TTC zone affects an accessible and detectable pedestrian facility, the accessibility and detectability shall be maintained along the alternate pedestrian route. [emphasis added]

Aha! This has implications because on one of my projects. I am proposing to close a bridge across an interstate for a weekend. During this time, I have to figure out how to get people over, under, around, or through the construction.

One idea is to set up a van shuttle from one side to the other, using the detour route. We shall see.

I had not been aware of that particular mandate in this most recent version of the MUTCD. Just goes to show that even “experts” don’t always know everything.

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Microblogging! Follow me on Twitter

I have found that the majority of the items I want to put up on the blog here, rather than the podcast, end up being eminently Twitterable. Thusly, I’ve decided that Talking Traffic needs a twitter feed! This serves the purpose of letting me tell you about fast turnaround items that aren’t really appropriate for the nature of the podcast.

If you’ve only heard about Twitter and never used it, or are possibly confused about it’s purpose or utility, fear not! Twitter is what you make of it. It is a service that allows people to post updates or information 140 characters at a time. Think of it as Facebook or Blogging in an extremely abbreviated form.

So if you want to get quick, late-breaking updates on transportation and traffic related items, go sign up for a twitter account and follow Talking Traffic.

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Twitter Question?

I’m going to ask this question in the next podcast also:

“Would you, the reader/listener, find a twitter feed dedicated strictly to Talking Traffic to be useful?”

I’ve found recently that there’s been a lot of items that could have been efficiently posted via Twitter regarding news stories or interesting things highway-related. These are things that don’t lend themselves well to the Podcast and I may not have the time to do a proper blog posting about them.

I could, of course, put them up on my personal Twitter account (and I have), but that stream is filled with all sorts of random garbage that you’ll probably not be interested in if you don’t know me personally.

Thoughts?

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Episode 35 – New Drivers Experiences

Topics: New Drivers, Interview

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Xkcd to the Rescue

Randall Munroe is the man.

Xkcd # 781

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