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Friday, 7 February 2020

What's a Watershed?

King City, Ontario
Depending on where you live, "watershed" may be a term you hear often. However, many people do not know what a watershed is, or how it is relevant to them.

Not long ago I had the opportunity to learn all about watersheds, but from the start found myself asking what constitutes as a watershed.

What is a watershed?

"the area of land that catches precipitation and drains into a larger body of water such as a marsh, stream, river, or lake" (SEAWA, 2014).

"A watershed is a topographically bounded area... that possesses a measurable drainage area (eg. 100 hectares), where all runoff from a precipitation event will be conveyed downstream, ultimately reaching the outlet of the area" (Introduction to Watersheds, 2020).

Imagine you are sculpting a shallow bowl with gently sloped sides. Now, if you were to add little peaks and indents on the inside of the bowl, you have just modified the topography of your bowl. After the bowl is finished, if you were to leave it out in the rain any rain that fell along the sloped edges would be funneled through the indents down to the lowest point in the bowl, maybe leaving other little pockets of water here and there.

topography: the physical appearance of the natural features of an area of land, especially the shape of its surface. - Cambridge Dictionary

In this analogy, not only middle pool of water but the entire inner surface of bowl is the the "watershed". It is an entire area of land that collects precipitation such as rain and drains it to a common place.

Watersheds exist in many different shapes, and can drain into many different types of water bodies. They are not limited to inland water bodies either; amoung water bodies such as lakes and large rivers, precipitation may also drain towards an ocean (Missouri Botanical Garden, 2002).


Cambridge. (n.d.). TOPOGRAPHY: meaning in the Cambridge English Dictionary. Retrieved from

Missouri Botanical Garden. (2002). Retrieved from

SEAWA. (2014). What is a Watershed? Retrieved from

Introduction to Watersheds. (2020). Introduction to Watersheds. Slide 3.

American Psychological Association 6th edition formatting by

edited 2020-02-11

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