Follow-up on flooding parking lot,

[micky]

This was the first paragraph of my first post about the parking lot that floods.

"How much water can a drain beside the road that is 4 inches high by 6 feet long, that feeds a 22 to 24" diameter pipe that is 50 feet long remove from the parking lot? It used to be as much as could rain on

109 townhouses, plus their yards and streets, but now it doesn't seem to be that much. Or it rains move than it did before. "

A couple days ago it occured to me. Arithmetic!!

The drain opening is 4" x 6' = 4 x 72 sq.in. = 288 sq. in.

The pipe is at least 22" in diameter, = pi x 11^2 = pi x 121 = 380 sq.in, in cross section.

So of course the drain opening limits what the pipe can carry.

288/380 = 0.76. The area of the drain opening is only 3/4s the cross-section of the pipe.

This would all be different if the drain opening were 8" high like it was 35 years ago when the n'hood was built. But two paving contractors putting down asphalt have laid the asphalt right up to the drain, taking off about 3 or 4 inches

Is there any reason the length of the pipe, 120 feet (not what I said before), could provide resistance** to water flow, so that the ratio right above would not be correct. After all the narrow part of the drain opening is only an inch long, and the pipe is 120 feet. If these were two wires of different diameter, the unequal lengths would make a big difference. OTOH, does it matter

**I can't google because I don't know what resistance (in electrical circuits) is called when dealing with water in pipes. ??????

The 2nd repaving was not the whole n'hood, just 2000 square feet that needed repair. Still it was a real paving company. Shouldn't they have known better than to pave riight up to a rain water drain? Doesn't that mean they should come out and cut out the drain obstruction for free? That's 5" horizontal (towards the roadway) x 4" vertical x

6 feet wide, the width of the drain. (only half of the thickness did they do.) How long could that take, an hour?

Then how long would it take to resurface what's left behind where they cut stuff out? That is, what about resurfacing the blacktop that is left, the bottom of the hole and especially the sides of the hole they cut. Won't they crumble if something is not done? Is it necessary? The equivanlent of rolling over the flat part of the road with a steam roller, or whatever they are called now.

That was not done before so of course we never paid for it. How long would that take them?

Thanks.

[dpb]

...

A) above is what I pointed out some time ago regarding the reduction in area. I don't recall the culvert dimensions being given previously but I suppose they probably were; just wasn't paying much attention...

B) flow resistance from surface is basically proportional to "wetted permiter" and it hasn't changed for the culvert. Given the geometry as I understand it, likely the biggest limitation is simply the gravity head as the water isn't channeled to the drain but is of whatever height develops so until it rises in front of the drain the full area isn't available, anyway. But, of course, once it does reach the depth of the full (constricted) height, it's slugged and that's the most it'll be able to take. Another 4" or so of height would add some head (actually

8" would be double that of 4" so while not large in absolute numbers, in percentages it's sizable).

C) The possible limiting factor from a geometrical standpoint other than simply the area constriction is the transition from the rectangular drain to the round culvert--is this just open transition or what?

I gave my opinion on the first step should be in the earlier response so won't repeat it here. I'd only amplify the likelihood of getting joy from the contractor who did it is probably inversely proportional to the length of time it's been since the work was done, and b) the new information that apparently two separate firms were involved so he's not responsible for the first half of it, anyway. So, ante-up and get it done and see if it's sufficient--can't be _that_ expensive even if don't get it gratis.

[micky]

There is a cement or concrete "lid" that's 6' long and about 3' wide. It has a manhole in it that no one ever removes, except perhaps the guy who vacuumed. There is a room below the "lid" that is almost 6 feet deep, so when the room is full, if it gets full, there is almost 4 feet of water above the entrance to the pipe.

But that doesn't keep the horizontal entrance from being obstructed.

There was a 14" whirlpool once the water level was low enough to display the whilrlpool.

It might have been a polar vortex. Have to get an expert to say yes or no.

That's fine. I read it and took notes.

Yes, probably two firms.

Thanks for the advice. I want to be prepared when I talk to the new president of the HOA. Not that I expect any trouble, but one never knows. The previous president didnt' hesitate afaict, to spend money on the vacuum or the little excavator, not because she cares if our 4 cars are flooded or not, but because it makes her feel important to spend money. The new pres could be a woman with 20 times the character of the first, but one of her good qualities might be going slow about spending money.

I don't like to call about business between Friday evening and early Monday morning, and something kept me busy last Thursday. (Did I miss a meeting of the HOA last Thursday? Hope not. ) I'll get her email address and that of whatever committee is responsible for this and then I can write any time.

The HOA may be liable if, after it's been given notice, it doesn't do enough. What it might do is notify the four of us to move our cars if it rains, and that's enough for a while, but after a while a reasonable person wouldl expect more.

Thanks.

[Randy333]

Flashlight. look down pipe. Any obstructions? Mud and silt build-up in bottom of pipe? I've seen pipes 1/2 way full.

Pictures?

Remove 333 to reply. Randy

[Pico Rico]

Best plan: remove the entrance obstruction as I posted weeks ago. Then wait for the next storm. Then tell us what happens. Then we go from there. Why are we beating a dead horse?

[micky]

I can't look down the mouth without lifting up the manhole cover and climbing down. I did look down the ... tail with a light. Could only see 10 feet but basically clean. Maybe a half inch of stuff. Maybe you missed it that a guy with a vacuum cleaner as big as a garbage truck came and vacuumed out the pipe. I couldn't see what was going up the tube, but I could hear it and there was quite a lot, and two chid's scooters got sucked and stuck to the end of his hose.

Now I'm going to find out if he did video of the whole 120 foot pipe. Probably did. Going to get his report. I just remembered that I did write the company name down, but I have no idea where that is.

Anyhow, if the property management office isn't totally mixed up, they'll be able to find the report, or at least the bill.

If they can't find it, that will make some more people want to change companies which woudl be fine with me.

The Baltimore area has about a million people. How many companies woudl own a vacuum cleaner that big?