Free-running creeks and rivers with their rapids and waterfalls aerate the flow, increasing its water purification and supporting salmonid fish. Watershed plant life modulates solar energy collection by shading the ground, humidifies and filters the air, and changes the color of the watershed surface compared to surface textures such as asphalt. The Forest Service has estimated that tens of millions of dollars in cooling bills could be saved by urban and desert-city reforestation and many millions saved in health costs. Watersheds act as valves of waterflow. They can convert runoff to storage in wetlands or percolate water into soil and bedrock reducing, for free, peak flood damage and flows.
Stable watersheds are the ultimate production systems for all animals, their food and shelter.
They are the most logical geographic unity for ecosystem management. They are the local green machines of photosynthesis. They prosper when the drainage net, channel, and hillslopes detain water and encourage growth. Green growth is a basic production, ultimately more important than industrial production. In short, drainage nets etch an equilibrium pattern into the watershed s surface.