Topics: Interview with Steve Williams
Topics: Interview with Steve Williams
Topics: Mast Arms, Strain Poles, Span Wires and other Signal Structures
Hello all. Here’s a list of what’s coming soon. The delightful news is that I have a lot of this in the can, and I just need to edit it down and get it up on the podcast.
So stay tuned!
Topics: “Child at Play” Signs, Sharrows, and Jewish Crosswalks
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.
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 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.
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.
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.
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:
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.