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June 22, 2012 6:24 PM

Why would a short section of street have 8-10 manholes?

There's a stretch of road about 4 blocks or so in length (for the Portlanders: SE Powell between 82nd and 86th, give or take) with nearly a dozen manholes. They aren't even in a straight line, but seem to wave a bit within the lane (which is a center/left turn lane). What purpose would there be for that many covers?

posted by curious nu to Technology (10 answers total)

Apart from providing access to sewers or storm drains, manholes often lead to concrete boxes the size of small rooms that are maintenance / junction points for various utilities - electrical, phone, or cable TV wiring, water or gas pipes, etc. I'd guess that if this group of access points are for different uses, they wouldn't have to match up exactly; in fact they might need to actually be staggered on purpose. Why all in that one clump, though, I couldn't tell you...maybe just coincidence? It looks like (via Google Maps) there's some sort of large residential or office building nearby as well as a fair number of businesses; perhaps that area experienced bit-by-bit growth so multiple expansions of multiple utilities were necessary over time.
posted by Greg_Ace at 7:10 PM on June 22, 2012

I just looked in that area in Google street view and I didn't see anything really out of the ordinary. I've got two in the intersection of 86th & Powell, and a couple more further down the street.

They aren't even in a straight line, but seem to wave a bit within the lane (which is a center/left turn lane).

Code requires some kind of cleanout at every turn for sewer lines, so that might be your answer right there.
posted by LionIndex at 7:46 PM on June 22, 2012

Two at 88th, two in front of Campbell's BBQ, and two at 86th. Going down Powell street, each pair seems to be in the same location.

It may be that one hole at each of the locations is for a turn in a branch line to intersect the main line running down Powell; the other hole is the actual intersection.
posted by LionIndex at 7:51 PM on June 22, 2012

There is a collection of 4 a bit further down the street. But yeah, I think this isn't really so odd and there may just be a gigantic sewer main below Powell.
posted by LionIndex at 8:00 PM on June 22, 2012

Response by poster: These are of very recent construction (3-4 months or so); I don't know whether or not the satellite imagery has been updated in that time and so that may not be a useful reference.
posted by curious nu at 8:27 PM on June 22, 2012

OK. I was looking at the street view, but that doesn't really contradict your point about the photo dates.
posted by LionIndex at 12:44 AM on June 23, 2012

I do not know the reason for a surfeit of manhole covers, but I would point out that until you give some thought to their presence and frequency (as you just have), it is very easy to not notice them. A few years ago I was living in Ottawa and read a news story about a rash of manhole cover disappearances which meant you need to watch your step in Ottawa in the most literal sense. 150 gone in one month, including 30 in one day. I initially thought that you would have to travel pretty far and wide to round up 150 manhole covers, until I took a look at the next corner I passed through (Somerset and Metcalfe, for those playing along at home on Google street view).

Counting anything within a car length of the intersection (and admittedly counting sewer grates as well), there were twenty-three at that corner alone.
posted by ricochet biscuit at 7:56 AM on June 23, 2012

There is more than one system underneath most older cities. Under the street of a city there can be electric, gas, sewer, storm sewer, fresh water, telephone/cable/internet, steam plus things that I'm forgetting. These things need to obviously be kept separate. (When sewer meets electric that's when underground explosions happen. You haven't lived until you've seen a manhole cover flying outside your third floor window.) In general each has it's own access/inspection point. If you can, take a look at the names on the manhole covers, they'll often tell you who owns what's underneath.

There could be an entire substation of some kind under there. Just because its paved over doesn't mean there isn't all kinds of construction down there. These things are generally placed under the street because they need to be within a certain area and there's no other reasonable place to build the service.
posted by Ookseer at 11:19 AM on June 23, 2012

Because I'm a giant dork, I went on Google Maps to look at the manholes. This one with a big S suggests Sewer, ditto this one.

And then I hit the manhole goldmine, because there was construction on Powell when Google drove by, so the utilities are all spraypainted on the street!

These three manholes are connected by green spraypaint, which indicates sanitary or storm sewer -- following the Z, there's 12" and 18" COPper STorm sewer, and then if you rotate clockwise you can see the 18" ST connect to a drainage grate. If you rotate counterclockwise you can see it extends over to actual construction in front of the little white and red sushi restaurant.

You can also see along there that electrical and phone run along the side of Powell (red and orange, respectively) so that plus all the manholes I could find having the matching "S" covers suggests that it's all sewer. I bet with Powell being so wide that there's a lot feeding into it that needs separate access.

There's also a water main running down the center of Powell (blue), which might explain some other manholes I couldn't see, but it's unusual to have a lot of manholes for fresh water midblock, just those tiny little access covers.

So from everything I can see marked there, most of the covers in that area are small (12-18") storm drains.

(I know nothing of Portland other than what I saw in those Street View pictures; the paint colors are a North American standard.)
posted by mendel at 4:21 PM on June 24, 2012 [1 favorite]

(Also this confirms that S manholes in Portland are sewer, not that there was much doubt. Incidentally, while you've got your eyes down, it appears that Portland's electrical manholes are pretty.)
posted by mendel at 4:25 PM on June 24, 2012