but how do mature trees stop run off? in general ground cover - grass and other low growing, dirt-covering plants are what stops sheet erosion and run off. Trees don't actually protect the surface of the soil from run off much, though their canopies do protect soil from hard rainfall, hail, etc.

as to basement, can you pin point where water comes in? is it a leak situation, under a door/window or is is seeping through masonry or other construction? surface run off can be diverted if it has someplace else to go, but if it is seepage below ground level that seems to be a situation where underground barrier/waterproofing would be needed.

The slope is gradual to my house and yard, and then gets very steep. The trees that were cut were in a row up the street just past my house. From what I remember from school, trees slow down runoff, either by the root system making it easier for water to absorb into the ground and by the canopy slowing the falling rain.

I'm on a corner lot. I used to watch the rain come flowing down the hill on the street past the trees. It stayed on the road in front of my house. During heavier rains, water would also flow down the side street and into my yard. We have railroad ties lying on their sides, partially buried in the ground. The water runs alongside and when it gets to the last rail, it goes into my yard. There's is a gap between the corner bed and the 1st rr tie, and I think they water is coming in there. Our neighborhood is built on sand. The next road is called Sand Hill.

The other neighbor has been cutting the cover on the other side of the street for years as well. I wouldn't be surprised if the whole hillside slides down someday.

There isn't a particular place the water comes in. Definitely on the corner and sides that face the hillside. The contractor is coming out and see what can be done.

Shrubs are faster growing than trees and closer to the earth.
Evergreen shrubs, not seasonal types.

I have a corner bed with several low trees and shrubs. I have to keep it cut way back so the neighbors have a clear view as they turn the corner.

The contractor iis coming out and I'll see what he has to say.

Thanks!