I wouldnt either, but if youre looking for the cheapest option that would be it.
This neighbor obviously gives zero fucks and just didnt want the water on his land anymore.
So the options are:
1. Wait for it to dry up to be able to mow, then deal with the creek anytime it rains heavy enough to overflow his retention pond.
2. Build a berm along your property about a foot higher than his property so all the water stays in his yard.
3. Dig a tench through your yard, fill it with rock to make a dry creek bed.
4. Dig a big ass trench, fill it with a culvert to bring water from his property under the road and out the other side, regrade and re sod/seed on top of culvert.
5. Raise enough hell that the DNR, and a bunch of people come out and agree with you that he re-routed a waterway and he has to fix it.
6. Ask him to dig it deeper and make a hydro-electric dam to power up a new building on the property.
Number one is obviously not an option if he's already aggravated at the water coming through the yard.
Number two shouldnt be THAT expensive, would block the water from coming into your yard, and once you put trees on top of the berm would look good as well.
Number three, would be not great looking but effective at being able to mow still instead of having a soggy moat in the middle of the lawn.
Number four would be a really good option, but ridiculously expensive.
Number five doesnt sound like much will happen based on the city phone call, but he might get lucky.
Number six is because I was bored.
Personally, I call everyone possible, if they tell me its not a problem I got to number 2 if I cant deal with it. Likely the cheapest option, wont look bad, and is also a big fuck off dickhead to him for trenching that shit over to your yard.
20 yard dumpster is 22' x 8' x 4.5' in size. 20 yards of fill dirt would be $400. Buying in bulk likely cheaper. I don't know how long his property line is, but a few 22' long, 8' wide, 4.5' berm would go a long way.