I have stone-and-cement retaining walls on two sides of my sloped driveway; they're new, and have cement caps. There's a long wall on the side of the driveway that's sloped about 1:20, and at the bottom end is a shorter wall that is sloped at about 1:40. The walls slope towards their mutual corner.
Water runs down the driveway towards both walls. The long wall is protected from water by a granite curb, but that just directs the water over the short wall. The water pours over the top of the wall and runs down the face and through the stones. I'm worried that this will harm the wall, especially with all the freeze cycles we endure in New England.
I want to add a second curb that protects the shorter wall from water, but which ends about 2' from the corner. Water would be directed through this gap, and somehow be brought away from the wall so it doesn't run down the face.
I can figure out how to choose and fasten the new curb (or I'll post a separate question): for the moment I'm looking for ideas on keeping the water away from the wall. An example would be to take some heavy rubber sheeting, glue it to the top of the wall, and drape it down the back of the wall, with the bottom edge ending in a trough to take the water away. But, I doubt the glue joint would last more than a season or two.
So, any ideas on how to protect the wall from water? (I'm also interested in comments on whether my worry is valid; it's a well-built wall, and perhaps it will just shrug off the water.)
Here are some pictures. First, from the driveway side; note the curb down the wall on the right:
Second, from the back of the shorter end wall. I'd want to have water coming over the corner at the left, but protect the wall from the water: