The force of water

We've lived in our house since 1978 and during that time we've had 5 different sets of neighbours living in the house at the bottom of the street. The hill is quite steep and our front driveway has a retaining wall on the left to hold up our garden and a retaining wall on the right to stop our driveway from falling into our neighbour's garden. 

Some time last year our neighbour, who moved into his house about 6 years ago, informed us that 1 i/2 paving stones on our driveway belonged to his property and he was going going to retrieve it.  We thought it was a silly idea as he can't make much use of the ground, but  today was the day when the work began. A digger and all sorts of containers arrived at 8am and the work began.  I thought no more of it and went into Glasgow as I had arranged, with my daughter and granddaughter.   
While we were in Glasgow there were very heavy rain showers, but there hadn't been much rain at home.  The removal of the paving stones had also taken place and they were piled up against our garage wall. At 6pm the heavens opened and there was torrential rain for about 30 minutes. The trench that was dug is now full of water, and the front of our driveway has partially fallen into the trench.  I have no idea what will now happen, but my worry is that if the rain continues, the exposed soil under the paving up the side of our garage will be washed away and the garage might collapse.  Hubby assures me that won't happen.

I originally took the blip of the rain on the window to show just how much rain we had today, before the catastrophe happened.