Watersheds of Cascadia

What is a watershed?  Despite its name, it’s not a backyard shed that holds water.  In its most basic sense, a watershed is an area of land.  It’s a land area in which every drop of rain that falls onto ground or bubbles up from a spring, drains to a common destination.  That destination could be a stream, lake, bay, ocean, or other body of water.  A watershed can be very large (such as the Amazon River – largest watershed in the world at 2.7 million square miles (7 million square kilometers))1, or could be as small as a suburban backyard.  No matter what land you are standing on though, you are in a watershed.

What separates watersheds?  Well, since water only flows downhill, watersheds are going to be separated by high points such as (in the most extreme case) mountains, but more often they are separated by simple hills.  Rain falling on one side of a hill is going to flow downhill into one stream while rain falling on the other side of the hill will go into a different stream.

Watersheds come in various sizes, smaller watersheds will make up larger watersheds.

Watersheds are the backbone of the Cascadia Bioregion.  The region itself is literally defined by the boundaries of watersheds in the northwestern United States, British Columbia, Alaska, and the Yukon Territory.  On the western edge of the Bioregion, we find the Pacific Ocean and the coastline of the United States and Canada.  If we head out Yellowstone National Park, we’ll find the most eastern edge of the Bioregion.  High up near a ridge, at about 9,200 feet in elevation, you’ll find the source of the Snake River which is the easternmost watershed in the Cascadia Bioregion.  On the southern end, the Eel River forms the watershed boundary in northern California.  At the northern end, we find the headwaters of the Aishihik River in Yukon Territory.  These are the cardinal extremes of the Cascadia Bioregion of which 16 million people call home.

Watersheds are important because the streamflow and water quality of a river are affected by things, human-induced or not, happening in the land area “above” the river. Watersheds are so critical for bioregionalism because, like Cascadia, they transcend arbitrary borders, and are critical in understanding where our water comes from, and where it goes, as well as engaging with all of the communities affected by that discussion. Creating these holistic cultural, economic, ecological and democratic systems are why ideas like Cascadia are so important.2

There are 15 major watersheds which make up the Cascadia Bioregion which have been defined and they are listed roughly from south to north:

  • Coastal Northern California – Mattole River, Eel River, Mad River
  • Klamath River
  • Coastal Oregon – Rogue River, Umpqua River, Tillamook River, Nehalem River
  • The Columbia River
  • Coastal Washington and Puget Sound
  • The Fraser River
  • Vancouver Island
  • Coastal Southern British Columbia
  • Haida Gwaii
  • The Skeena River
  • The Nass River
  • The Stikine River
  • Southern Boundary Ranges
  • Northern Boundary Ranges
  • Alsek River and Gulf of Alaska

While there are 15 major watersheds which average about 38,485 square miles (99,676 square kilometers) each – about the size of the US State of Kentucky.  There are a total of 423 smaller-scale watersheds which each measure on average 1,364 square miles (3,535 square kilometers) – a little larger than the US State of Rhode Island.

The Columbia River is the largest watershed in the Cascadia Bioregion, alone comprising about 260,000 square miles (670,000 square kilometers) – approximately 45% of the entire area of the Bioregion; however, the Columbia is made up of many smaller watersheds, the largest of which is the Snake River.  As mentioned, the headwaters of the Snake River begin in the US State of Wyoming and the river empties into the main stem of the Columbia River in central Washington.  The Columbia begins its journey in southern British Columbia (in the Canadian Rocky Mountains) and then flows approximately 1,200 miles until it reaches the Pacific Ocean.  To the east, the Columbia River watershed is delineated by the crest of the Rocky Mountains, in the north by the Monashee Mountains, in Washington, the Cascade Mountains form the western boundary of the watershed.  To the south, the watershed is bounded by the mountains that ring the northern extent of the Great Basin, an endorheic basin draining parts of the western states of Oregon, Nevada, Utah, Arizona, and California.  Finally, in Oregon, the watershed is defined by the crest of the Calapooya Mountains and Oregon’s Coastal Mountain Range.  The Columbia River sneaks through the Cascade Mountains at the Columbia River Gorge before finally emptying into the Pacific Ocean.  In looking at the smaller-scale watersheds within the larger Columbia River watershed, we find that the Columbia has 174 smaller watersheds (approximately 41% of the Bioregion’s total).

The Fraser River watershed is the second largest watershed in the Cascadia Bioregion covering 90,000 square miles (233,000 square kilometers) – approximately 16% of the entire Bioregion.  The Fraser River watershed lies just to the north of the Columbia River watershed and extends up to the Skeena and Hogem Mountain ranges in the north and the Coast Mountains of British Columbia on its western side.  It flows through the gap between the Cascade Mountains and the Coast Mountains before emptying into the Salish Sea near Vancouver, British Columbia.  In looking at the smaller-scale watersheds within the larger Fraser River watershed, we find that the Fraser has 68 smaller watersheds (16% of the Bioregion total).

The Haida Gwaii watershed is the smallest of the major watersheds of the Cascadia Bioregion.  It only covers 3,900 square miles (10,100 square kilometers) – 0.6% of the whole Bioregion.  The Haida Gwaii watershed is bounded on all sides by water.  To the north, the Dixon Entrance – a strait between Alaska and the islands, to the west and south, the Pacific Ocean.  The Queen Charlotte Sound is to the southeast, and the Hecate Strait to the east.  In looking at the smaller-scale watersheds within the larger Haida Gwaii watershed, we find that it has 2 smaller watersheds (0.5% of the Bioregion total).

We all reside in a watershed of the Cascadia Bioregion.  Whether your home watershed is defined by a series of mountain ranges or small hills, whether it is a larger watershed or a smaller one, or whether you live near a river’s headwaters or it’s mouth, is less important in the grand scheme of things because when these watersheds are all combined together, they define the boundaries of the place we call home: the Cascadia Bioregion.



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