We live in a side-split and have a problem with shingle damage caused by water run-off from the upper roof to the lower roof. The damage is so bad that we have a large patch over the damaged shingles until our new roof is installed. What has me confused is that our previous roof handled water run-off without a problem. Why are the shingles we have now being damaged so badly? -- an installation problem? bad shingles? something else? I'm hoping someone can look at the pictures below and suggest cause(s). I would also like to hear suggestions of things we can do when we replace this roof so that we don't have this problem again. As I said, our house is a side-split. In the first photo you can see how water from the upper roof is directed down a small section of roof that links the upper roof to a valley that then channels the water in the opposite direction and down the lower roof. On the extreme right side of this picture, you can see the top of the patch covering the worst of the damaged shingles. Here is a shot of the lower roof and the 2-foot wide pathway where the run-off from above runs down to the bottom of the roof. The second photo shows the shingles at the bottom of this 2-foot wide pathway. These photos show the valley between the upper and lower roofs in more detail. Any ideas about the cause of this problem and how to avoid it in future would be very much appreciated. Thanks.