Watersheds

Why do you think this drain is lower than the ground around it? Think about what happens if you are washing your car and splash some water onto the street. You will probably notice that the water does not flow outward in all directions, but instead goes in only one direction and ends up in one big puddle at the end of your driveway.

Why is this so?
 

The answer is gravity—water always flows downhill, and it will follow the one path that goes from a higher elevation to lower elevation, even if the difference is only a few centimeters.

Likewise, on a larger scale, all water on Earth follows a downhill path as it runs over the ground surface. Like the puddle at the end of your driveway, the water that runs downhill will congregate in one place. The place where all the water drains to is called a watershed. All the water from a watershed will eventually end up in a river, lake, or ocean. It is like the drain in the picture—a place to where all the water flows.

Why is the term "drainage basin" an appropriate synonym for the term "watershed?"
 

Think of a basin like a large tub or bucket. A watershed is really like a large precipitation collector, or a large basin in which water collects after running over the land’s surface.

All watersheds are a system made up of parts that work together to do work. They comprise both living (biotic) and non-living (abiotic) factors. The work done by watersheds includes:

• transporting water
• transporting energy
• carrying sediments (all the particles of soil and rock carried by steams from one place to another)

What are biotic factors of a watershed?
 

Biotic factors include all the living things, like aquatic organisms that live in rivers, like fish and alligators; trees and shrubs; the deer and rabbits that live in a forest around a lake; and of course, the humans that interact with the watershed environment.

What are the abiotic factors of a watershed?
 

The abiotic factors are the non-living things, like the air, the water, the rocks, soils, and sediments.