Key Subbasin Issues

Altered flow regimes, particularly during low flow periods in late summer, resulting from reduced winter precipitation and an increase in the number and magnitude of diversions;

High instream temperatures in many streams, with above lethal temperatures recorded in the late summer in Tenmile Creek, the East Branch SF Eel River, and the middle and lower mainstem SF Eel River;

High levels of fine sediment input related to high road density and erosion from landslides, construction waste, and ground disturbance on unstable soils;

Low percent canopy density and poor quality pool habitat (depth, shelter, and cobble embeddedness) in most surveyed Eastern Subbasin streams;

High gradient streams with natural (primarily waterfalls) or anthropogenic (culverts) barriers limiting anadromy;

Addition of fertilizers, pollutants, and sediment to streams from marijuana cultivation operations in watersheds with high residential land use;

Sacramento pikeminnow documented in mainstem SF Eel River and in some Eastern Subbasin tributaries.

Responses to Assessment Questions

What are the history and trends of the sizes, distribution, and relative health and diversity of salmonid populations in the Eastern Subbasin?

The Eastern Subbasin supports populations of Chinook salmon, coho salmon, and steelhead trout;

Using data from one long term data set for salmonid populations in the SF Eel River Basin (Benbow Dam counts occurring from 1938-1975), trend lines for Chinook salmon, coho salmon, and steelhead trout abundance all show significant decreases throughout the sampling duration. These trends are most likely similar for salmonid populations throughout Eastern Subbasin streams;

Populations of all three salmonids appeared to decline abruptly following the 1955 and 1964 floods;

Current salmonid populations are not only less abundant, but they are less widely distributed than they were historically:
  • Historical and anecdotal accounts in 46 Eastern Subbasin streams dating back to the late 1930s indicate the presence of presence of Chinook salmon in 12 tributaries (26% of streams sampled), coho salmon in 25 tributaries (54% of streams sampled), and steelhead trout in 36 tributaries (78% of streams sampled) in the Eastern Subbasin;
  • Current salmonid distribution, based on data collected for 167 Eastern Subbasin streams from a variety of sources (CDFW, USFS, tribal fisheries monitoring, university research, local watershed stewardship programs, and additional fisheries stakeholders) indicate the presence of Chinook salmon in 27 tributaries (16% of streams), coho salmon in 17 tributaries (10% of streams), and steelhead trout in 44 tributaries (26% of streams) in the Eastern Subbasin;

Historically and currently, steelhead trout have been found in more tributaries and in areas further upstream than both Chinook and coho salmon. This is due to their preference for habitats that are located farther inland, in smaller streams than Chinook and coho salmon (Moyle et al. 2008), their ability to tolerate a broader range of instream conditions, and their comparatively superior jumping abilities;

Eastern Subbasin streams have higher gradients than most Northern and Western subbasin streams, but steelhead are able to access high quality habitat in upper areas in many tributaries (e.g. Tom Long, Cruso Cabin, and Cedar creeks);

Non-native Sacramento pikeminnow have been documented in most surveys beginning in the late 1990s and are now common in areas of the mainstem SF Eel River and in lower reaches of many tributaries. Pikeminnow compete with and prey upon juvenile salmonids, and are adapted to withstand warmer water temperatures than native salmonids.
What are the current salmonid habitat conditions in the Eastern Subbasin? How do these conditions compare to desired conditions?

Flow and Water Quality

Instream flow in many streams has been reduced through unpermitted diversion for residential uses and marijuana cultivation, particularly in areas where land use is primarily residential (e.g. near Garberville, Redway, and Laytonville). Reduced flow (compared to historical averages) has been documented in Eastern Subbasin streams during the late summer and early fall;

Low summer flows result in dry or intermittent reaches on streams, which may be stressful to salmonids and lead to juvenile mortality;

The recent increase in industrial marijuana cultivation coupled with several drought years has led to increased development or reliance on groundwater wells, which will only further exacerbate low flow conditions in the summer and early fall;

Water diversion by industrial timber companies for road dust/sediment control has been estimated at 2,000-4,000 gallons/mile/day between May 15th and October 15th. The amount of water used may be substantial at a time when stream flow is already low, particularly in areas with multiple users with high water demand;

Water quality is reduced by input of fine sediments from roads throughout the subbasin, primarily seasonal roads that were originally used to access or haul timber. Many of these roads are now also used to access residential areas in newly developed locations or where larger parcels have been subdivided;

Water quality is also reduced by marijuana cultivation operations, which may input of fertilizers, pesticides, rodenticides, diesel fuel from generators, and sediment from improperly constructed roads, and clearing and construction activities at grow sites;

Increased turbidity is stressful to salmonids, especially during the rainy winter months. High levels of turbidity occur during salmon and steelhead spawning season.


Excessive sediment in stream channels has resulted in an overall loss of spawning, rearing and feeding habitat for salmonids. High sediment input from natural and anthropogenic sources have resulted in low suitability pool habitat and reduced water quality in Eastern Subbasin streams;

Road density is relatively high (2.88 miles/square mile) in the Eastern Subbasin, which is the lowest density of all three SF Eel River subbasins but is still high enough to negatively affect the ecosystem and aquatic species by reducing water quality and increasing watershed degradation (Carnefix and Frissell 2009). Legacy logging roads and the use of substandard logging roads for hauling timber and for residential purposes are a significant source of sediment input to streams throughout the subbasin;

Pacific Watershed Associates (2001) stated that the most important element necessary for long term restoration of salmon and steelhead habitat in the East Branch of the SF Eel River is the reduction of accelerated erosion and sediment delivery to the stream system. Upgrading and decommissioning existing roads were the primary recommended treatments;

Soils in the Eastern Subbasin are prone to erosion, and landslides and streambank failures contribute fine sediments to streams throughout the subbasin;

Two streams in the southern part of the subbasin, Mud Creek and Mud Springs Creek, receive constant fine sediment input from natural mud springs near Cahto Peak, but Mud Springs Creek has substantially less suspended sediment than Mud Creek, which appears milky throughout the year;

During the historic flood events of 1955 and 1964, very large quantities of sediment entered Eastern Subbasin streams, and legacy effects of the sediment input are still influencing these streams;

Increased fine sediment in stream gravel has been linked to decreased fry emergence, decreased juvenile densities, reduced diversity and abundance of invertebrates, loss of winter carrying capacity, and increased predation (Gucinski et al. 2001).

Riparian Condition/Water Temperature:

Canopy density met or exceeded target values (>80%) in more than half of the streams sampled in the Eastern Subbasin in the 1990s and early 2000s, however, values were significantly below target values in Tenmile Creek during both sampling periods.

In the 1990s, 51% of the stream length surveyed had canopy densities below 50% and only 49% met target values of 80% or greater. Coniferous canopy cover was relatively low (< 50%) in most streams, and was less than 10% in Bond Creek, Hollow Tree Creek, Michaels Creek, and an unnamed tributary to Durphy Creek;

In the early 2000s, 40% of the stream length surveyed had less than 50% canopy density, 20% had canopy densities of 50-79%, and 40% of surveyed stream length met target values of 80% or greater;

Canopy density suitability improved or stayed the same over time in most Eastern Subbasin streams, but decreased in areas of Cahto and Big Rock creeks. In the early 2000s, suitability scores were in the lowest category in upper and lower Tenmile Creek, and in the second lowest suitability category in the middle reaches of Tenmile Creek and the lower reach of Big Rock Creek;

Coniferous canopy was very low (<25%) in most Eastern Subbasin streams during both sampling periods. The percent coniferous canopy decreased over time in Bear Canyon, Cahto, and McCoy creeks, and increased over time in Milk Ranch, Mud, SF Bear Canyon, and Tenmile creeks;

Water temperature data collected by HCRCD (between 1996-2003), and ERRP (in 2012) indicated poor (≥66ºF) instream temperatures at 11 tributary sites and 9 mainstem SF Eel River sites; fair (63-65˚F) instream temperatures at three tributary and one mainstem sites; and good instream temperatures (50-62˚F) recorded at 12 tributary and one mainstem locations in Eastern Subbasin streams. There were four sites where lethal (≥75ºF) conditions were recorded: two in the mainstem SF Eel River near Piercy (RM 54) and Sylvandale (RM 25), one in Tenmile Creek, and one in the East Branch SF Eel River;

Bouma-Gregson (UC Berkeley) recorded average daily temperatures above lethal levels (≥75˚F) on 15 days between July and August 2013 in the mainstem SF Eel River at Richardson Grove (RM 49), and on nine days in July 2013 at Standish-Hickey State Recreation Area (RM 66);

High temperatures in Eastern Subbasin streams are a result of a combination of reduced riparian cover, lower summer flows, warmer air temperatures due to the lack of influence of the coastal marine layer, and aspect (little afternoon shade).

Instream Habitat:

Three Eastern Subbasin streams met the >40% target value for pool depth when sampled between 1990 and 1999: Cahto Creek (1996; 45% primary pool habitat), McCoy Creek (1995; 48% primary pool habitat), and Tenmile Creek (1996; 64% primary pool habitat). All three of these tributaries were sampled again between 2000 and 2010, and percent primary pool habitat dropped well below target values. The remaining 7 streams surveyed did not meet target values for primary pool habitat, and values ranged from a high of 38% in Tenmile Creek in 2009 to a low of 0.4% in McCoy Creek in 2007;

Quality pool structure is lacking in Eastern Subbasin streams. The average mean pool shelter rating was 69.1 in the 1990s and 27.0 using habitat data collected between 2000 and 2010. These values are well below the target pool shelter value of 100 for salmonids. Pool shelter decreased in both rating value and suitability between the 1990s and early 2000s;

Boulders were the dominant pool shelter type during both sampling periods. Using habitat data collected in the 1990s, other shelter types were terrestrial vegetation and undercut banks; in the early 2000s, other shelter types were terrestrial vegetation, root masses, and SWD. LWD was not documented as a pool shelter type in the 1990-1999 sampling period, and was only the dominant shelter type in one reach surveyed between 2000 and 2010, indicating that LWD is lacking in all sampled Eastern Subbasin streams;

Although pool depths were generally shallow, pool-riffle ratios were above optimal ratios (1:1) in Eastern Subbasin streams during both sampling periods, and the percentage of pool habitat relative to riffle habitat increased slightly in recent years (2000-2010) compared to percentages recorded on surveys in the 1990s. In the 2000s, the pool riffle ratio was 61:39, which is generally considered to provide suitable holding area and habitat diversity for both juvenile salmonids and benthic invertebrates;

More than 50% of the total stream mileage in Eastern Subbasin tributaries is >10% gradient. Many ends of anadromy occur at boulder roughs or waterfall barriers.


Cobble embeddedness conditions improved in all Eastern Subbasin streams over time, with average category 1 embeddedness values of 10.5% for data collected in the 1990s and 28.5% for data collected between 2000 and 2010. Although embeddedness values increased, they were still below target values (>50% category 1) during both time periods;

The percent of pool tails surveyed in cobble embeddedness category 1 nearly tripled between the 1990s and early 2000s. The percent of pool tails in category 2 stayed nearly the same, and the percent of pool tails in embeddedness category 3 was reduced by more than 50% between the two time periods. Only categories 1 and 2 are suitable for salmonid spawning;

Low substrate embeddedness suitability for salmonids in Eastern Subbasin streams in the 1990s was due to extensive sediment input from highly erosive soils, active landslides, roads, and historical flood events. Suitability scores increased as a result of sediment from historic floods moving through the system, and restoration projects including road decommissioning and bank stabilization. Most of these restoration projects have been completed as part of the East Branch SF Eel /Reed Mountain Watershed Restoration Implementation Project.

Refugia Areas:

Salmonid habitat conditions were generally rated as medium potential refugia (21 of 31 rated stream areas), meaning that most Eastern Subbasin streams have degraded or fragmented instream and riparian habitat, with salmonids present but reduced densities and age class representation. Salmonid habitat may improve with modified management practices and restoration efforts;

Elder Creek was the only Eastern Subbasin stream rated as high quality refugia habitat. This creek is part of the University of California Natural Reserve system, and the habitat is relatively undisturbed, with conditions necessary to support species diversity and natural production;

Three streams were rated high potential refugia: McCoy Creek, Cedar Creek, and the upper mainstem SF Eel River (beginning at RM 92). Cedar Creek flows primarily through land managed by the USBLM (the Red Mountain unit), and this stream contains excellent steelhead habitat. The upper mainstem SF Eel River provides good salmonid habitat due to cool instream and air temperatures, topography that includes many steep walled canyons and narrow valleys, and fewer diversions than in other areas within the Eastern Subbasin;

Six tributaries were rated low quality: Dean Creek, lower East Branch SF Eel River, Fish Creek, Cummings Creek, Mud Creek, and Cahto Creek. Most of these creeks are located in residential areas and are heavily diverted. Instream habitat is characterized by high stream temperatures, poor canopy cover, low flow, high sedimentation rates, and poor water quality. Current conditions and management practices have modified the natural environment extensively, and major changes are required to improve habitat conditions in these areas.

Barriers and Other Concerns:

Both natural barriers (landslides, gradient, and LDA) and anthropogenic barriers (culverts and dams) were mapped using information from stream inventories, field reconnaissance, and the CalFish Passage Assessment Database;

Most of the barriers identified were gradient barriers (n = 28), followed by culvert barriers (12 partial and 15 total);

The most common type of gradient barriers in Eastern Subbasin streams were waterfalls, and the largest waterfall (22’) documented by CDFW crews is located on Fish Creek;

Most culvert barriers, both total and partial, were located at road crossings along the mainstem SF Eel River, Rattlesnake Creek, and Tenmile Creek, where Highway 101 and smaller roads leading into individual basins cross tributary streams. Three culverts that are partial barriers to fish passage are located in the headwaters of the SF Eel River, where Branscomb Road crosses Rock Creek, Kenny Creek, and Wise Gulch;

There are two dams in the Eastern Subbasin, one of which is considered a total barrier (Grapevine Creek) and one is currently unassessed (unnamed tributary to Cahto Creek);

Benbow Dam, located on the mainstem SF Eel River at RM 40, is not currently a barrier to fish passage, but it has been in the past (when flashboards were installed each summer to form a recreational dam) and it is currently being considered for removal.