How would you handle this drainage problem?

[Plombob]

There are two holes in the backyard of a property I own that I need to resolve before they get any larger. It's been developing for over a year.

When I first saw these holes, I thought an animal was digging in the yard, so I put gravel down to discourage them. We've had some heavy rains and the holes enlarged quite a bit. That's when I realized that one hole is possibly a drain pipe and the other is a drain that routes under the driveway.



The reason I believe one hole is a drain pipe is that it goes straight back 4 feet. The tape measure shows the direction of the hole. There is no evidence of an intake anywhere in the yard.

The direction doesn't make sense for a drain because it is going across the yard, not downhill to the street, unless it was connected to the drain under the driveway. But there is no evidence of a broken pipe that connected the two holes.



Closeup of the entrance to the 4 foot hole.



The other hole appears to be a drain which runs under the sloped driveway. There is a ditch at the end of the driveway by the street. I ran water into the drain for a half an hour and could not find any water in the ditch. I could not find where the water went.



I'm thinking of running 4" drain pipe into the hole the water comes out of, to a catch basin, and then from the catch basin to a pipe that goes into the drain under the driveway. I could skip the catch basin and just run a pipe between the two holes.

How can I determine if I run a risk of undermining the driveway if I connect the two holes?
Is there an advantage to placing a catch basin before the drain that goes under the driveway?
Would you dig up the drain and reroute it? I'd like to avoid this because of the expense. The distance from the yard to the ditch at the street is very long.
How would you resolve this?

 

[The Cobbler]

maybe someone in the drain cleaning business with a camera & locating probe could help you find out what's what .

 

[whitesco]

Throw a handful of lady finger type firecrackers in there and listen for the echo…





That will have no helpful information for you at all to the best of my knowledge, but that’s what I’d do for the entertainment value.

 

[carlaisle]

The first thing I would do is figure out what is actually happening. You have evidence that dirt is moving, but no evidence of how this occurring. You suspect water erosion. Some smoke and a fan can be a big help in determining if there is any connection between those two holes. If you asked this a month ago I would have suggested visiting the nearest fireworks stand. You can also buy smoke candles that are made for this purpose. Any small fan will do. A poncho and downpour could also prove instructive, although scheduling could be less convenient. The camera mentioned above and/or a shovel could also help shed some light on the matter.

 

[ALinCarolina]

Not sure what kind of soil you have there but we have heavy clay. Where the power company plowed in the cable to our house took over 10 years to collapse down in spots and show up. It will be interesting to find out what that is.

 

[Plombob]

Throw a handful of lady finger type firecrackers in there and listen for the echo…





That will have no helpful information for you at all to the best of my knowledge, but that’s what I’d do for the entertainment value.

Well, you aren't far off from what carlaise proposed!

The first thing I would do is figure out what is actually happening. You have evidence that dirt is moving, but no evidence of how this occurring. You suspect water erosion. Some smoke and a fan can be a big help in determining if there is any connection between those two holes. If you asked this a month ago I would have suggested visiting the nearest fireworks stand. You can also buy smoke candles that are made for this purpose. Any small fan will do. A poncho and downpour could also prove instructive, although scheduling could be less convenient. The camera mentioned above and/or a shovel could also help shed some light on the matter.

That's some good advice. We can get fireworks all year round (go figure!) but it's a bit of a drive.

Not sure what kind of soil you have there but we have heavy clay. Where the power company plowed in the cable to our house took over 10 years to collapse down in spots and show up. It will be interesting to find out what that is.

The soil isn't heavy clay, but it has some clay. This is an old area, the lines are all above ground, so it can't be a cable. I doubt it would be a gas line because they typically run up from the street, not across everyone's backyard.

I don't know why I didn't think of having a plumber come out with his scope. I'll

 

[Rusty Wrench]

Some smoke and a fan can be a big help...

+1 on the smoke.

A fiberglass probe rod ($10-15) is what I've often used. If the soil is hard; keep a gallon jug of water handy. work the rod in a couple inches. add water- work the rod, add water. You'll know if your hitting hard pipe. Place a pin flag at the hole to see how direction and depth is trending. It goes quicker than you'd think.

How can I determine if I run a risk of undermining the driveway if I connect the two holes?
Is there an advantage to placing a catch basin before the drain that goes under the driveway?

Any drainage conduit under the drive needs to be hard piped. It can be drain pipe w weep holes but you gotta have pipe.
Catch basin at the start of the drainage is always a good idea.

Do you currently have a drainage problem?

I'm thinking of running 4" drain pipe into the hole the water comes out

I ran water into the drain for a half an hour and could not find any water in the ditch. I could not find where the water went.

Having trouble reconciling these 2 statements. I think a sketch would help

Edit to add: You can buy smoke bombs for the purpose finding blind sewer runs/connections. Our surveyors supply store stocked them.

 

[Plombob]

I had a plumber run a scope down the two holes in the yard. Turns out the one under the driveway wasn't a drain. It didn't go very far. We enlarged the opening of the other hole and discovered it was a massive gopher den.

I filled both holes with 12 bags of large river rock, small river rock and crushed rock. Then I topped them off with concrete, then put topsoil over the concrete. The concrete will keep gophers from opening it up again.

 

[ybnormal]

I had a plumber run a scope down the two holes in the yard. Turns out the one under the driveway wasn't a drain. It didn't go very far. We enlarged the opening of the other hole and discovered it was a massive gopher den.

I filled both holes with 12 bags of large river rock, small river rock and crushed rock. Then I topped them off with concrete, then put topsoil over the concrete. The concrete will keep gophers from opening it up again.

so where was all the dirt they were digging out being moved to?

 

[Plombob]

That's a very good question. There was no pile of dirt around the hole. That's what got me thinking it was created by water and not an animal.

 

[racecougar]