Drainage channels refer to pathways or structures designed to collect and carry away water. They are like "canals" that help prevent water from flooding or pooling in certain areas. Full definition
Not only are there the different levels and kinds of browsing and grazing, but mechanical effects such as pan-making, path - making, soil aeration, seed dispersal, keeping waters open, maintenance of drainage channels (the hippopotamus) and fertilization of waters (the hippopotamus, waterbuck and lechwe antelope). (scientificamerican.com)
Build an ice cap on that; you get water and silt being extruded out of the basins, even flowing «uphill» under that pressure; look at the radar maps, the ice may have pushed a lot of silt out to its edges over time, you can see the pattern of river drainage channels in the radar imagery. (rabett.blogspot.ru)