Drainage Issues From Neighbor
Since we moved into our property 8 years ago our neighbours have leveled and paved their entire garden and path which leads down the side of both our properties. They are at a higher level than us by about 2 foot. Outside their back gate they have placed what looks like guttering which feeds onto our property outside our backgate. Whenever they hose down their garden (which is quite frequently) all of their rubbish (which has recently included dog poo) drains into our back garden and across the patio then drains slowly into the grass.
As we need to approach them about this I was wondering what advice you could offer to help them with their drainage as I feel what they have done is not appropriate!
I can't really give advice to your neighbors as I would have to see there property and what areas (other than your property!)they could divert their water too.
However, I will tell you that in the U.S. it is illegal for someone to change their land in any way so that water from their property flows onto an adjacent neighbor's property in a capacity that is more than before any changes were made. If that is true where you live, legally they are in the wrong.
I am sure the best route (as you have indicated) is to talk to them to see if they will change things. I doubt it, as it sounds like they went through an expense to create what they did. How far you want to go legally is up to you, but I do believe you have legal recourse.
If you would like to send me photos I'd be happy to take a look though.