Water run-off, drainage, SINK HOLES?!

[IamwhoIsayIam]

We have two holes that have appeared in our garden over night, both about 1ft in diameter x 1ft deep. I was looking at them today in the rain, a little stream was running along the the path leading behind all our terraces then ran down into it and literally disappeared. The path is just hard pack soil, and the holes are in the edge of our lawn.

Problem is the holes are very close to my neighbours wall, although in my garden. I need to get it investigated/fixed whatever but I have no idea who to call. Any ideas on a) what might cause this suddenly happening and b) what expert or trade needs to come and take a look.

Terrace is 100 years + old. Could be an old soak-away drain? Filled in well or just natural water action?

Is this one for @PigletJohn

I think you need to contact your insurers in the first instance. They should be able to advise you further. You need to find the cause be it a collapsed sewer or something else.

Are you in an old mining area? I had a 30ft hole which opened up overnight in the garden around 20 years after we had the house underpinned due to a collapsed mineshaft under the kitchen whilst renovating it.

First stop insurers, then you may be asked to get a surveyor. We used a specialist mining engineer.

@HewasH20 - that sounds frightening! There is no record of mining in the area on historical maps and nothing came up in searches so I don't think it will be that. (I hope!)

I was hoping to find a bit of advice and someone to look at it before I got in touch with insurers so I have a rough idea what I'm dealing with.

Structural engineer? Drainage engineer? I honestly I have no idea even what to google.

I've known broken drains cause cavities in the ground, commonly they are next to a house and the paving (or sometimes the wall) collapses into it when the hole gets big enough.

If it's a broken drain or waterpipe, the old pipe is visible at the edges of the hole, with water coming out of it either during rain, or when you pull out the bath plug. Broken drains are fairly straightforward to repair, but old unsuccessful attempts will have to be dug out and renewed. There is often old concrete or mortar in an attempt to fill or hide the hole or patch the break.

I've also seen holes open up where an underground structure has been covered over or filled in, and the earth has settled. Here you can see the old brickwork or concrete in the hole

I have no experience of underground streams or mining work. A local surveyor or builder should know if they are found in your district, and, if so, some knowledge of what to do.

Insurance may help, especially if the house has been damaged.

There's no damage to property and the area around the two holes seems stable - I have prodded and stood on it.

I have gone for a drainage and ground works engineer as a starting point.

The house near to the holes is a second home with owners not seen from one month to the next. No one near by has contact details from them. I'm going to investigate a little bit further then see whether it needs insurance. At that point I'll put a note through the door or try to find a mailing address through land registry.

I'd call my insurance as they would appoint a suitable engineer themselves, be careful that it doesn't get worse as you don't know what has caused it. Yours or a neighbouring house could end up damaged and then you will need to engage insurance and I'd think they would ask why this wasn't your first call tbh.