What is a watershed?

A first step in watershed exploration (like most any academic or professional pursuit) is to define what you are exploring and explaining.  A simple definition:        A watershed is the area of land where all of the water that is under it or drains off of it goes to the same place.

John Wesley Powell, scientist geographer, described a watershed as:

    "that area of land, a bounded hydrologic system, within which all living things are inextricably linked by their common water course and where, as humans settled, simple logic demanded that they become part of a community."

Watersheds, sub-watersheds, and micro-watersheds:

Larger watersheds such as the Chesapeake Bay Watershed can encompass many hundreds of
smaller watersheds (tributaries of the Susquehanna River, Elk River, Potomac River, Patapsco, Patuxant, James and others).  Even these tributaries include many smaller watersheds, including micro-watersheds that may not even be named.  

One strategy for appreciating the relationships of smaller watersheds and larger watersheds is to imagine the flow of water resulting from rainfall on a specific place. One could follow the flow from a yard or parking lot to a drainage “ditch” or swale to a small, identified stream.  This small stream may travel several miles until its “mouth” or confluence with another or larger stream.   

That stream may flow toward a river that joins a larger river and even a larger river before it empties into the Chesapeake Bay or Gulf of Mexico.

In urban areas, watersheds often begin as storm sewers that are aggregated and may be “daylighted” as they feed into small streams, often in urban parks.