Key Issues

High levels of fine sediment input related to very high road density and timber harvest activities on unstable soils;

Altered flow regimes, particularly during low flow periods in late summer, resulting from diversion and reduced winter precipitation patterns;

Addition of fertilizers, pollutants, and sediment to streams from marijuana cultivation operations in watersheds with high residential land use (e.g. Redwood Creek);

Erosion from landslides, roads, construction waste, and ground disturbance;

Poor quality pool habitat (depth, shelter, and quality) in most Western Subbasin streams;

Medium potential refugia habitat in lower Redwood Creek (Redway), which was historically a productive coho and Chinook salmon and steelhead trout stream;

High instream temperatures in many streams, with above lethal temperatures recorded in the late summer in the mainstem SF Eel River;

Sacramento pikeminnow documented in mainstem SF Eel River and in some Western 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 Western Subbasin?

The Western 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 Western 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:

o Historical and anecdotal accounts in 50 Western Subbasin streams dating back to the late 1930s indicate the presence of presence of Chinook salmon in 17 tributaries (34% of streams sampled), coho salmon in 28 tributaries (56% of streams sampled), and steelhead trout in 41 tributaries (82% of streams sampled) in the Western Subbasin; o Current salmonid distribution, based on data collected in 175 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 44 tributaries (25% of surveyed streams), coho salmon in 34 tributaries (19% of surveyed streams), and steelhead trout in 53 tributaries (30% of surveyed streams) in the Western 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;

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 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 Western Subbasin? How do these conditions compare to desired conditions?

Flow and Water Quality:

Instream flow has been reduced through unpermitted diversion for residential and marijuana cultivation uses, particularly in areas where land use is primarily residential (e.g. Redwood Creek near Redway). Reduced flow (compared to historical averages) has been documented in Western 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 the 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 which are now also used to access residential areas in newly developed locations or where subdivision of larger parcels has occurred;

Water quality is reduced by marijuana cultivation operations. Water quality is compromised in these areas by the 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 streams throughout the subbasin;

Road density is high (4.8 miles/square mile) in the Western Subbasin, which is the highest density of all three SF Eel River subbasins, reflecting the dominant land use of industrial timber harvest. Legacy logging roads and use of substandard logging roads for hauling and residential access are sources of sediment input into streams throughout the Western Subbasin;

Soils in the Western Subbasin are prone to erosion, and slides and streambank failures contribute fines to the streams;

During the historic flood events of 1955 and 1964, very large quantities of sediment entered Western Subbasin streams, and legacy effects of the sediment input are still influencing Western Subbasin 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 in the early 2000s in nearly all surveyed streams in the Western Subbasin. Canopy density values increased over time (using habitat typing data collected during two time periods: 1990-1999, and 2000-2010); the largest increase was seen in Low Gap Creek, where mean canopy density increased by 60.2% between surveys conducted in 1990 and in 2007;

In the 1990s, 25% of the stream length surveyed had canopy densities below 50% and only 43% 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, there was no stream length with less than 50% canopy density, and 85% of surveyed stream length met target values of 80% or greater;

Canopy density suitability improved over time, and most Western Subbasin streams were in the highest category in in the early 2000s. Suitability scores were in the lowest category on the lower reaches of Redwood Creek (Redway), and in the second lowest suitability category on lower Sproul Creek;

The average percent of coniferous vegetation increased and percent open canopy decreased considerably in most Western Subbasin streams over time;

Water temperature data collected by HCRCD (between 1996-2003), and ERRP (in 2012) indicated poor (≥66ºF) instream temperatures at 5 tributary sites and 9 mainstem SF Eel River sites; fair (63-65˚F) instream temperatures at 8 tributary and 1 mainstem sites; and good instream temperatures (50-62˚F) recorded at 40 tributary and 1 mainstem locations in Western Subbasin streams. There were two sites where lethal (≥75ºF) conditions were recorded, both in the mainstem SF Eel River near Piercy (RM 54) and Sylvandale (RM 25);

Bouma-Gregson 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 9 days in July 2013 at Standish-Hickey State Recreation Area (RM 66).

Instream Habitat:

Only one surveyed stream met the >40% target value for pool depth: Redwood Creek (tributary to Hollow Tree Creek) had 42% of surveyed habitat length classified as primary pool habitat in 2003. The remaining 43 streams surveyed did not meet target values for primary pool habitat, and values ranged from a high of 34% in Indian Creek in 2008 to a low of 0% in two streams: an unnamed tributary to Durphy Creek in 1993 and Lynch Creek in 1991;

Quality pool structure is lacking in Western Subbasin streams. The average mean pool shelter rating was 43.5 in the 1990s and 36.4 using habitat data collected between 2000 and 2010; these values are well below the target pool shelter value of 100 for salmonids. Pool shelter was the only habitat component analyzed that decreased in both rating 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 SWD, LWD, undercut banks, and terrestrial vegetation. Using data from the early 2000s, other shelter types were LWD, SWD, undercut banks, terrestrial vegetation, root masses, and whitewater;

Although pool depths were generally shallow, pool riffle ratios were above optimal ratios (1:1) in Western Subbasin streams, 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 60:40, which is generally considered to provide suitable holding area and habitat diversity for both juvenile salmonids and benthic invertebrates.


Cobble embeddedness conditions improved in most Western Subbasin streams over time, with average category 1 embeddedness values of 12.7% for data collected in the 1990s and 34.4% 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 nearly 50% between the two time periods. Only categories 1 and 2 are suitable for salmonid spawning;

Low substrate embeddedness suitability for salmonids in Western 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.

Refugia Areas:

Salmonid habitat conditions were generally rated as high potential refugia (38 of 57 rated stream areas), meaning that these streams have diminished but good quality habitat with salmonids present. Most are currently managed to protect natural resources, with the possibility to become high quality refugia;

Five Western Subbasin streams were rated as high quality refugia habitat: Indian, Moody, Anderson, Low Gap, and Upper Hollow Tree creeks. These are creeks have relatively undisturbed habitat, with conditions necessary to support species diversity and natural production;

Only two tributaries were rated low quality (Connick and Little Charlie creeks). These watersheds have few salmonids and highly impaired riparian and instream habitat, mainly because of water diversions for residential and agricultural uses. Current conditions and management practices have modified the natural environment extensively, and major changes are required to improve habitat conditions in these areas;

The remainder of the tributaries rated (12 of 57) were rated as medium potential refugia, meaning that instream and riparian habitat is fragmented, and salmonids are present but in reduced densities and age class representation. Western Subbasin streams in this category were most of the Redwood Creek (Redway) watershed, lower Hollow Tree, lower Connick, Sawmill, Durphy, and Hartsook creeks.

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 culvert barriers, both total and partial, were located at road crossings along the mainstem SF Eel River, where Highway 101 and smaller roads leading into individual basins cross tributary streams. Two partial culvert barriers are located in the Hollow Tree Creek drainage on land owned by MRC;

There are two culvert barriers located on Dinner Creek, both of which are total barriers to fish passage. The first culvert is located 8.3 miles up Briceland Thorn Road from Redway (RM 0.85 from China Creek confluence) and the second culvert is located 8.8 miles up Briceland Thorn Road (RM 1.39 from China Creek confluence). Ross Taylor and Associates (2005) recommended replacing both existing culverts with properly sized new culverts that provide unimpeded passage;

Benbow Dam is located on the mainstem SF Eel River at RM 40. This is not currently a barrier to fish passage, but it has been in the past and is being considered for removal;

One dam was identified on Jack of Hearts Creek. This was an earthen dam that was built in the summer, but is no longer installed and is not currently considered a barrier to fish passage;

Forty gradient barriers, mostly waterfalls, were identified in Western Subbasin streams if they occurred in areas other than natural ends of anadromy in headwater areas. These barriers may be partial (a barrier to certain species or life stages), total, or temporal (only a barrier at certain times of the year).

What are the impacts of geologic, vegetative, fluvial, and other natural processes on watershed and stream conditions?

Natural erosion rates in the Western Subbasin are high due to the following conditions:

o All rock types in the SF Eel River Basin are considered lithologically soft, prone to erosion, and sensitive to land use. The major rock type underlying the Western Subbasin is the sandstone/argillite/conglomerate of the Coastal Terrane, which tends to form sharp-crested ridges with well-incised sidehill drainage and is susceptible to debris sliding especially upon steep stream banks and inner gorge areas; o The Western Subbasin is located in one of the most seismically active regions in North America, and fault movement can result in uplift or subsidence of the local landscape, increasing the potential for erosion or deposition; Floods periodically occur due to high winter precipitation levels and high runoff rates;

During the rainy season, heavily silted water flows from steep upstream terrain, downstream to lower reaches, increasing turbidity and sediment levels in many subbasin streams;

The predominant vegetation type is mixed conifer and hardwood forest, covering 73% of the Western Subbasin area. The average percent deciduous canopy was greater than coniferous canopy in surveyed streams, but the percent coniferous canopy increased between the late 1990s (17%) and early 2000s (22%).

How has land use affected these natural processes?

Changes in basin due to land use:

The majority (75%) of the land in the Western Subbasin is used for industrial timber harvest, and is owned by Mendocino Redwood Company and Hawthorne Timber Company. There is less harvest activity now than in the past, and newer forest practices and management actions (including road decommissioning) have prioritized habitat preservation and fisheries habitat management;

Road density is higher in this subbasin (4.8 miles/square mile) than in either the Northern (3.7 miles/square mile) or Eastern (2.9 miles/square mile) subbasins. Most roads were originally built to access and haul timber, but many are now also used to access marijuana cultivation sites and residences, especially in areas where large parcels have been subdivided into smaller lots;

Sediment input from land use activities, primarily roads and timber harvest, is particularly problematic in this subbasin due to highly erodible soils and active landslides;

In the Redwood Creek (Redway) drainage, the primary land use is residential, and there has been a substantial increase in the number of marijuana cultivation operations in this watershed. In 2012, there were 549 grows (226 outdoor and 323 indoor) identified in this drainage alone, with an estimated 16.5 million gallons of water per growing season required to support these operations (Easthouse 2013). Water sources include direct diversion from streams, groundwater wells, and storage tanks, but little is known regarding how much water is supplied by each source.

Possible effects seen in stream conditions:

Instream habitat conditions for salmonids are poor in some streams:

Low summer flows are exacerbated by diversions, which result in dry or intermittent reaches on streams (especially those that are affected by diversion), which are stressful to salmonids;

In addition to low flows, water quality (temperature, pollution, turbidity) decreases in areas with high levels of instream diversion and input of fertilizers, chemicals, sediment, and waste from grow operations, resulting in decreased habitat suitability for salmonids;

Excessive sediment in stream channels has resulted in an overall loss of spawning, rearing, and feeding habitat for salmonids. Sediment input from both natural (landslides and streambank erosion) and anthropogenic (timber harvest and road failures and/or degradation) sources are high, with correspondingly high turbidity levels which are stressful for salmonids. Substrate embeddedness values were high in most surveyed reaches, but have shown significant improvement over time;

Average pool depth and pool shelter values did not meet target values in surveyed Western Subbasin streams (n = 44);

Boulders were the dominant shelter type in pools, followed by LWD and SWD. Average percent shelter from LWD was less than 5% for data collected during both sampling periods.

Erosion related to timber harvest and roads on unstable soils is a concern:

Industrial timber harvest occurred in most areas in the subbasin prior to the 1960s, and continues to be the primary land use in more than 75% of the subbasin. Historically, and to a lesser extent currently, sediment enters the streams from timber harvest activities and road related input, including both chronic erosion of fine sediments and catastrophic failure of roads prisms during winter storms;

Timber harvest, while less of an issue than in the past, still occurred in the headwaters of nearly all Western Subbasin streams between 1991 and 2013. Erosion related to timber harvest is a concern throughout the subbasin due to highly erosive soils, active tectonics contributing to unstable slopes, and heavy rains received during winter months. Logging roads, which are often also used for residential purposes, are significant sources of fine sediment input to streams;

Timber harvest impacts were magnified by the 1955 and 1964 floods, and sediment pulses from historic land use practices and floods are still moving through Western Subbasin streams.

Based upon these conditions trends, and relationships, are there elements that could be considered to be limiting factors for salmon and steelhead production?

Based on available information for this subbasin, it appears that salmonid populations are limited by:

Low summer flows;

High summer water temperatures in the middle mainstem and downstream, and in larger tributaries;

High levels of fine sediments in streams, mainly from roads and timber harvest activities;

Loss of habitat area and complexity, particularly primary pool habitat and pool shelter;

Competition with Sacramento pikeminnow.

What watershed and habitat improvement activities would most likely lead toward more desirable conditions in a timely, cost effective manner?

Most habitat recommendations from surveys conducted in Western Subbasin streams targeted instream habitat, including pool and cover categories. Most other recommendations targeted erosion/sediment (related to streambanks and roads) and riparian habitat/water temperatures (canopy and temperature);

Road decommissioning projects are particularly important in this subbasin due to the very high road density and intensive historic and current timber harvest activities;

Mendocino Redwood Company, Trout Unlimited, CDFW, and USFWS collaborated on a comprehensive restoration program in the Hollow Tree Creek watershed. This program involves upgrading all roads within the watershed, decommissioning roads that are no longer needed, and installing instream habitat enhancement structures. Three phases of restoration were originally planned, beginning in 2003 and extending through 2008, but additional projects and improvements are currently being completed. Monitoring to determine if these activities result in reduced sediment input to streams is ongoing, and additional problem roads may be identified and projects completed in the future;

Support ongoing efforts by timber harvest review agencies to quantify water usage by industrial timber companies for road dust abatement/sediment control, and support actions designed to encourage efficient use of water;

Ensure that water diversions used for domestic or irrigation purposes bypass sufficient flows to maintain all fishery resource needs;

Support and expand projects designed to address solutions to low flow during the late summer months by reducing the number and magnitude of diversions (e.g. SRF’s water conservation project in Redwood Creek). Public outreach is needed to increase awareness of land use practices and their impacts on the basin’s natural resources;

Restoration activities that will create additional pool habitat and scour existing shallow pools, while reducing sediment input from roads, are highly recommended throughout this subbasin;

Identify areas where marijuana cultivation is occurring and quantify environmental effects at sites, including illegal diversions (especially during low flow times), input of pesticides and other pollutants, and sediment loading from these practices. Enforce existing regulations and develop new environmental regulations to target these activities;

Replace two culverts in Dinner Creek that are total barriers to fish passage. The County of Humboldt recently submitted a proposal for FRGP funding to replace both culverts, in addition to a smaller culvert approximately 700 feet upstream from the second culvert;

Conduct an upslope erosion inventory in order to identify and map stream bank and road-related sediment sources. Sites should be prioritized and improved;

Wood recruitment is low in most Western Subbasin streams, and projects that add LWD to streams are recommended. These projects could be combined with pool habitat creation/enhancement projects, since both primary pool habitat and pool shelter are limiting factors for salmonids in this subbasin;

Consider replanting of native species, like willow, alder, redwood and Douglas fir in areas with little or no native vegetation, or in areas with non-native vegetation;

Consider thinning hardwoods to increase growth of conifers where riparian forest is strongly dominated by hardwoods and shade canopy will not be adversely affected;

Monitor streams near land development activities and existing rural residential areas for turbidity, pollution, and drainage issues;

Continue to conduct biological sampling through the CMP to determine salmonid population abundance and diversity, including but not limited to current CDFW redd counts, adult spawner surveys, and carcass counts, with funding requested to establish and operate of a life cycle monitoring station in Sproul Creek in 2015;

Consistently collect water quality data, including temperature, dissolved oxygen, and water chemistry throughout the year for several years in order to accurately characterize conditions. Support programs and organizations such as SRF and ERRP that develop studies to monitor the flow, temperature, diversion, and water quality of streams throughout the subbasin, particularly in developed areas.