Ooh! an old stone-built box-culvert! Underground history!, this'll be early1800s, let's take the top slab off-
The bright green is drain-tracing dye, we'll be looking for it in the drain to which we THINK this might connect...
Oh dear... It's going nowhere, just filling up the trench. More excavations then... better go get a mini-digger.
Let's play "Pass the Buck".
We can, legally, says the water-board man, just leave a hole and let the water spill out over the city's unmaintained land.
And if it floods a house, rented from the city, then there's no claim against us, because it's just surface water, and it was running through this land long before the city built houses on the farmland, and they failed to identify and locate all pre-existing drainage. And they allowed trees to grow over the drains/sewers/culverted water-courses.
Still, every cloud has a silver lining. From old experience I know this makes good earthenware potting clay, maybe I'll get a trailer-load.