Answer:
The legal definition of a drainage can be found in Idaho Administrative Rules (IDAPA) at 13.01.11.004.10 which says:
10. Drainage. All water flowing into a common river or stream system, either above or below ground, due to area geography.
You can find other common definitions used to craft fish rules in this same section of IDAPA.
Answered on:
Monday, September 28, 2015 - 8:19 AM MDT