The concept of watershed is a very important one because it pertains to everyone. No matter where someone lives, they live in a watershed. A watershed (also called a drainage basin or a catchment) is defined as an area of land that intercepts and drains precipitation through a particular river system or group of river systems. In other words it is a region of interconnected rivers and streams which functions as a unified system for water transport. The term can be used with reference to a particular stream, river, lake or ocean (although it is sometimes also confusingly used to describe only the high point of land which divides two regions of drainage).

A watershed is the land area that drains into a body of water. For example, imagine that a bowl is a watershed. The rim of the bowl represents the highest peaks of the mountains surrounding a valley with a river below, the bottom of the bowl. The inner walls of the bowl represent all of the smaller hills and mountains in the valley. Only water that falls on the rim and the inner walls of the bowl will enter the river, all other water that falls outside of the bowl rim and inner walls will flow in a different direction, or to a different watershed. Watersheds are so important because water that is polluted anywhere in the watershed, even if it is hundreds of miles away, will eventually flow into the estuary. It is crucial to keep the water in the estuary clean, as well as all of the water that will eventually flow into the estuary, to maintain a healthy environment for the plants and animals that live there.

You're Sitting In A Watershed Now

• Everyone resides in a watershed. 

• Every place on the earth is a part of a watershed. Homes, farms, ranches, forests, small towns, big cities and more can make up watersheds. 

• Some cross parish, state, and even international borders. 

• Watersheds come in all shapes and sizes - some are millions of square miles &  others are just a few acres. 

• There are many living and non-living things in watersheds. 

• Watersheds are constantly changing.   

A watershed is like a bathtub. The watershed outlet - the mouth of a pond, lake or river- is the tub's drain. The watershed boundary is the tub's rim. The watershed's drainage system consists of a network of rivers, streams, constructed channels, storm drains, wetlands, and the underlying groundwater.

Gravity and topography are the two major factors that define a watershed.  Gravity is the unrelenting force of nature that pulls all water downhill. Topography describes the form of the land: the hills, valleys and other features that influence where and how water will flow. After saturating the ground, rain or meltwater trickles downhill in tiny rivulets that coalesce into larger ones that eventually combine into streams. These then merge into rivers that finally flow into the ocean. (Perhaps stopping temporarily in water bodies such as lakes.) Gravity and topography help define these channels of water from the tiny to the huge and cause them to join together into stream networks. These water-flow structures frequently resemble the branching pattern of trees or blood vessels.

The term watershed or catchment basin refers to the entire physical area or basin drained by a distinct stream or riverine system, physically separated from other watersheds by ridgetop boundaries."

Every channel (or lake) of a given stream network drains an area of land around it known as its watershed. Like a stream network is made up of component channels, a given watershed is also comprised of component watersheds. These, in turn, are made up of still smaller component watersheds, and so on. (See red boundary lines in image at left) Watersheds can range in size from tiny to many thousands of square miles.

Watersheds allow us to evaluate the quality and quantity of our water resources geographically. Only by knowing our local watershed and the system of watersheds in which it resides can we begin to understand why and where small changes can have huge impacts on our state's water. Human and natural modifications made in one watershed may be spread many miles downstream to another. Understanding this "domino-effect" is critical to the monitoring and managing of our state's water resources.

Watersheds may be of various forms: a closed watershed empties into an inland body of water, whereas an open watershed drains to the ocean. A multiple open watershed empties into the ocean through more than one mouth. A watershed is defined topographically by break points or ridges (e.g., mountain crests) which separate it from the next watershed.

What Is A Watershed?

Watersheds 101

Watershed Connections

Where The Rivers Meet The Sea: 2. Watersheds

Forest Hydrology and Watersheds