Emerging Coastal Network | Pacific Coast Watershed Partnership

Lower Columbia River Watershed | Columbia River National Scenic Area


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	Skagit Dungeness Lower Columbia Siuslaw Umpqua Coquille


	6th field HUC Maps:

	Skagit Dungeness Lower Columbia Siuslaw Umpqua Coquille

The lower Columbia estuary (lower 145 miles to Bonneville Dam) is one of the largest and most important salmonids rearing areas in the North Pacific (LCREP ). The surface geology of the Coast Range portion of the estuary is dominated by Miocene and Pliocene sedimentary and volcanic rock (Schuster 1992, Walker and Macleod 1991). The upper portion of the estuary cuts through the Andesite and basalts of the High Cascade Mountains to form the Columbia Gorge. The dominant salmonids found in the estuary are: Chinook, coho, chum, steelhead, and cutthroat trout. It has been said that historically there was a run of salmonids returning to the Columbia estuary every month of the year (Northwest Power Planning Council 2000) . The dominant cause of habitat destruction in the lower Columbia has been associated with draining and diking the wetlands and floodplains for agricultural uses and urban development (LCREP). Also, the constructions of the mainstem Columbia River dams has lead to significant changes in the magnitude and timing of floods and the amount and nature of the organic matter entering the estuary.

The lower Columbia is one of the largest estuaries in the North Pacific. It is generally defined as the lower 145 miles of the mainstem up to the Bonneville dam. It also includes portions of the Willamette River up to the falls at Oregon City (LCREP). The zone of salt-water intrusion is considered to generally include the lower 46 miles of river.

The Columbia estuary cuts through the Coast Range and High Cascades Mountains. Below Bonneville Dam for about 20 miles the river is narrow generally less than 1,000 feet. This reach is now the designated as the Columbia River Scenic Gorge, with its steep canyon sidewalls and high waterfalls. The surface geology of the High Cascades is primarily Pleistocene and Pliocene basalts and andesites. More than 20 miles downstream of Bonneville Dam the river widens out with a broader floodplain. Numerous sloughs and islands are located from St. Helens to the mouth. Below St. Helens, the floodplains are broad with steep bluffs as the river passes through the Coast Range. The surface geology of the Coast Range includes Miocene marine sedimentary rock and Miocene Columbia River basalts.

The dominant salmonids of the lower Columbia include: chinook, coho, chum salmon, steelhead and cutthroat trout. The Columbia was one of the greatest salmonids fish producing rivers in the world and it was considered to have the world's largest Chinook salmon run (NWPPC 2000). It has been estimated that 16-18 million salmonids annually entered the river. It is claimed that during each month of the year some life-history of Pacific salmon were returning to the river. Currently, 12 species of salmon and steelhead are listed as threatened or endangered. Overall production of anadromous salmonids is under 10% of the historical levels and hatchery production accounts for approximately 75% of the returning adults.

In addition to the salmonids, the lower Columbia river estuary is an important feeding and breeding grounds for shellfish (oysters, clams, crab and mussles) and sturgeon. It is also one of the most important sites on the Pacific Flyway for migratory birds. Over 175 species of birds use the lower Columbia (LCREP).

Much of the lower estuarine floodplain, wetland, and riparian habitats have been widely lost to diking, filling, and shoreline development activities. Historic diking, filling, shoreline development, and other activities have removed many of the shallow, wetlands and isolated the lower Columbia River and estuary from its floodplain. Since 1870, more than 50% of the tidal marsh and swamp habitat has been lost in the lower Columbia (NWPPC 2000). Also, 70% of the tidal wetland in the lower 46 miles of the estuary as been lost since 1948 (NWPPC 2000). As of 1980, only 35% of the former area of marsh and swamp habitat remained in the Columbia River estuary (NWPPC 2000). In addition, the upper river dams have significantly altered the magnitude and timing of floods and it has altered the amount, type, and timing of organic matter entering the river.

Economically the lower Columbia is also important nationally. Five deep-water ports are located in the lower Columbia between the mouth and Portland, 110 miles inland (LCREP). These ports comprise the 2nd largest port on the West Coast. Approximately 40% of the nation's wheat exports are shipped via the lower Columbia. Other major exports include corn, logs, and paper. The lower Columbia is a major import site for automobiles.

Literature Cited:

Lower Columbia Estuary Program. Lower Columbia River Estuary Plan.

Northwest Power Planning Council. 2000. Return to the River. Council Document 2000-12. Schuster, J.E. 1992. Geologic Map of Washington. Washington Department of Natural Resources.

Walker, G.W. and N.S. MacLeod. 1991. Geologic Map of Oregon. U.S. Dept. of Interior. Geologic Survey.