Basin Overview

The Eel River catchment is large and complex, and it has been divided into several basins for assessment: the South Fork (SF) Eel River Basin; the Lower Eel River Basin (including the Salt River), and the Van Duzen River Basin. The SF Eel River Basin assessment area makes up approximately 19% of the entire Eel River catchment and is defined as the watershed area from the confluence with the Mainstem Eel, upstream approximately 105 miles. The mainstem SF Eel River receives flow from 450 tributaries, adding up to 885 miles of stream. The South Fork of the Eel River runs from its headwaters near the town of Branscomb, located in northern California, approximately 140 miles north-northwest of San Francisco at latitude 39° 36' 37" N, longitude 123° 30' 07" W, to its mouth near the town of Weott approximately 200 miles north-northwest of San Francisco at latitude 40° 21' 22" N, longitude 123° 55' 06" W. The SF Eel River Basin lies within Humboldt and Mendocino Counties.

For the SF Eel River assessment, the basin was divided into three subbasins: Northern, Eastern, and Western.  In general, these subbasins have distinguishing attributes common to the CalWater 2.2.1 Planning Watersheds (PWs) contained within them. These subbasins were designated based on several attributes, including geography, geology, climate patterns, aspect, vegetation, and land use; variation among subbasins is a product of both natural and human disturbances.

General attributes of the South Fork Eel River Basin
Attribute Northern Subbasin Eastern Subbasin Western Subbasin
Area (square miles) 149 320 219
% of basin 22 47 32
Miles of stream 216 435 387
Principal Communities Weott, Myer’s Flat, Miranda, and Phillipsville Redway, Garberville, Benbow, Piercy, Leggett, Laytonville, and Branscomb Briceland
Dominant Geology Yager terrane Central belt mélange Coastal terrane
Dominant Vegetation Mixed conifer and hardwood forest Mixed conifer and hardwood forest Mixed conifer and hardwood forest
Dominant Land Use State Parks, Forestry Forestry, ranching/timber, residential Forestry
Salmon Species Coho, Chinook, Steelhead Coho, Chinook, Steelhead Coho, Chinook, Steelhead

Coho salmon and steelhead populations in the SF Eel River and Mattole River were selected by the North American Salmon Stronghold Partnership as “strong populations”, populations considered critical to sustain viable salmon populations throughout their range. Chinook salmon, coho salmon, and steelhead have been documented in fish surveys in all three SF Eel River subbasins, but salmonid distribution and abundance are greatest and habitat conditions are most suitable for salmonids in Western Subbasin streams.