What is a watershed?

Watershed Perspective Courtesy of Lane Council of Governemnts

Watershed Perspective
Courtesy of Lane Council of Governemnts

A watershed is the entire area draining into a specific body of water, such as a river or creek. Watersheds are composed of uplands, riparian areas, wetlands, lakes, streams, and rivers. One watershed is separated from another by ridgetops.

How big is the Tualatin Watershed?

It is 712 square miles (455,680 Acres)

The Tualatin River is approximately 83 miles long and flows from the eastern side of the Coast Range to the Willamette River.

The Tualatin River is a fourth-field hydrologic unit (HUC 17090010)

What type of climate does the watershed have?

Mediterranean climate with prolonged winter rainfall and summer drought

Hillsboro Yearly Temperature

Hillsboro Yearly Temperature

Mean winter air temperatures in the valley floor:  32º F to 63º F (0º C to 17º C)

Mean summer air temperatures in the valley floor:  41º F to 83º F (5º C to 28º C)

Hillsboro Yearly Rainfall

Hillsboro Yearly Rainfall

Rainfall varies from 100” to 120” in the Coastal Range to 48” to 36” in the valley (inches per year)

What are the major tributaries?

Tributary Statistics

TributaryDrainage Area
Square Miles
River Mile of
with the
Tualatin River
Scoggins Creek45.119.260.0
Gales Creek77.923.556.8
Dairy Creek23110.5545
.......West Fork Dairy Creek25.6
.......East Fork Dairy Creek22.9
Rock Creek75.619.338.1
Fanno Creek32149.3

Are there any reservoirs in the watershed?

Scoggins Reservoir (Henry Hagg Lake)

Barney Reservoir on the Trask River releases water to the Tualatin River during the summer months.

Where is the Tualatin River Watershed located?

Most is in Washington County

Small sections are in Clackamas, Tillamook, Multnomah, Columbia, and Yamhill counties

How do I find out the current flow of the river?

The river’s flow is measured in cubic feet per second (cfs) and can be found at these sites: US Geological Survey http://or.water.usgs.gov/tualatin/ and the Oregon Water Resources Department flow site: http://apps.wrd.state.or.us/apps/sw/hydro_near_real_time/Default.aspx.

The first time you go to the Oregon Water Resources Department flow site on a given computer, it is helpful to set it up so it goes directly to the Tualatin Basin flow stations.  This only has to be done once per computer.

      • Click on (Login)  under My Stations on the right side of the page
      • In the box for your email address type: OWRD_Hydro_predefined_district_18
      • Click on Return to Gage Search Menu
      • Now it will say (Manage) under My Stations on the right side of the page
      • Click the drop down menu for My Stations and click on District 18
      • Now only the Tualatin River flow stations will be listed (Both OWRD sites and USGS sites will be listed).

What Cities are located in the Tualatin Watershed?

Banks, Beaverton, Cornelius, Durham, Forest Grove, Gaston, Hillsboro, King City, North Plains, Sherwood, Tigard, Tualatin, West Linn. A large portion of the urbanized area is in unincorporated Washington County.

What is the population of the Tualatin Basin?

Approximately 450,000 (US Bureau of Census, 2001)

Washington County has grown 43 % in the last 10 years

What are the predominant uses of the land in the Tualatin Watershed?

20 % Urban

30 % Agriculture

50 % Forestry

Who owns and/or manages the land?

93% is privately or municipally owned

5% is managed by the State of Oregon

2% is managed by BLM

What are the water quality issues?

The Department of Environmental Quality issued Total Maximum Daily Loads for Dissolved Oxygen (excess oxygen-consuming organics and ammonia), Temperature, Bacteria, and Chlorophyll a (excess phosphorus) for the Tualatin Basin in August 2001.

Are there species on the Endangered Species List in the Tualatin Basin?

Winter Steelhead are listed as threatened

What types of wildlife can be found in the basin?

Roosevelt elk, black-tailed deer, and black bears are found in the Coastal Range

An estimated 5,000 Canada geese and 65,000 ducks winter in the basin.

Bald eagles, osprey, herons, hawks and many more birds live in the basin.

What are the recreational opportunities?

Canoeing on the Tualatin River

Canoeing on the Tualatin River

The Tualatin Riverkeepers have a recreation guide.

There are many parks and trails.

Hagg Lake is open to boating and fishing.

Many people enjoy canoeing on the Tualatin.




What are the economic drivers in the Tualatin Basin?

Agriculture; horticulture; forest products; food processing; high-tech, including software and electronics; sports equipment; and apparel (Oregon Blue Book)

What is the economic productivity?

Washington County is ranked 4th in state for gross farm and ranch sales with $204 million (Oregon Department of Agriculture 2001)

Washington County is ranked 2nd county in state for retail sales (US Census Bureau: 1997 Economic Census)

Per capita personal income $30,621 compared to Oregon average of $23,920 (1998 figures)