However, note of caution. There's a difference between slight "collecting of water" and creating reservoirs or dams. The common law views creating reservoirs or dams as "abnormally dangerous activity" because of the danger it poses to others. Normally someone doing that is liable for harm if the dam or reservoir brakes no matter how careful the person is. A law limiting this kind of activity is not necessarily unjust.
The heavy rainfall is in the coastal mountains and west slope of the Cascade Mountains. Central Oregon and eastern Oregon have deserts or high deserts with dry scrub most of the year.
Normally someone doing that is liable for harm if the dam or reservoir brakes no matter how careful the person is. ....So? Sue me.