Key Findings

Historical accounts and stream surveys conducted in the 1960s by CDFG indicate that the Northern Subbasin supported populations of Chinook salmon, coho salmon, and steelhead trout. Fishery surveys have been conducted on very few tributaries in the Northern Subbasin in the last ten years. Therefore, current fish population information is poor. However, existing recent biological stream surveys indicate the presence of healthy steelhead trout populations but an absence of coho salmon. Mattole Basin-wide data indicate a depressed population of Chinook salmon, which likely indicates a depressed number of Chinook salmon spawners in the Northern Subbasin;

Erosion/Sediment
Instream sedimentation in several stream reaches in this subbasin may be approaching or exceeding levels considered unsuitable for salmonid populations. Macroinvertebrate data indicate fair to good or good conditions. However, amphibians sensitive to fine sediment were absent from most stream reaches surveyed in this subbasin;

Riparian/Water Temperature
High summer water temperatures in surveyed streams are deleterious to summer rearing salmonid populations in this subbasin;

Instream Habitat
In general, Northern Subbasin pool habitat, escape and ambush cover, water depth, and substrate embeddedness are unsuitable for salmonids. Large woody debris recruitment potential is very poor overall;

Gravel Substrate
Available data from sampled streams suggest that suitable amounts and distribution of high quality spawning gravel for salmonids is lacking in this subbasin;

There is a lack of stream survey and water chemistry information for much of the Northern Subbasin;

This subbasin has the most structurally disrupted and least stable geology in the basin, with approximately 43% of the area underlain by soft terrain. Correspondingly, more than half of the total area occupied by historically-active landslides and gully lengths mapped in the basin are located in the Northern Subbasin. Due to the prevalence of soft terrain with its associated high level of active landslides and gully erosion, it appears that comparatively high rates of natural sedimentation are to be expected in this subbasin;

Stream channels in this subbasin have the greatest total length of features indicative of excess sediment production, transport and storage within the basin, with the smallest reduction in these features observed between 1984 and 2000;

Grasslands are extensive in the Northern Subbasin, occupying 31% of the area. Grasslands are commonly associated with soft terrain. As a result of past timber harvest and conversion activities, 40% of the Northern Subbasin is occupied by small diameter (twelve to twenty-four inches diameter at breast height) forest stands. Only 7% is in forest stands greater than twenty-four inches. The most significant vegetation change in recent years was the result of two 1990 wildfires burning 10% of the subbasin, primarily in the Oil Creek and Camp Mattole planning watersheds;

Over 99% of this subbasin is privately owned and is managed for timber production and grazing. Current timber harvesting is concentrated on industrial timberland subject to both the California Forest Practice Rules and a Habitat Conservation Plan. Existing road location and densities primarily reflects construction related to timber harvest access since the 1940s;

Based on information available for the Northern Subbasin, the NCWAP team believes that salmonid populations are currently being limited by high water temperatures, high sediment levels, and reduced habitat complexity in the subbasin.

Recommendations

Flow and Water Quality Improvement Activities

Where current canopy is inadequate and site conditions, including geology, are appropriate, initiate tree planting and other vegetation management to hasten the development of denser and more extensive riparian canopy. Low canopy density measurements were found in Conklin, Oil, Green Ridge, Devils, and Rattlesnake creeks;

Erosion and Sediment Delivery Reduction Activities

At stream bank erosion sites, encourage cooperative efforts to reduce sediment yield to streams. CDFG stream surveys indicated Sulphur Creek, Sulphur Creek Tributaries 1 and 2, Conklin Creek, Oil Creek, and the lower reaches of the North Fork Mattole River have bank stabilization activities as a top tier tributary improvement recommendation. Rattlesnake, McGinnis, Green Ridge, and Devils creeks also have eroding banks mapped by CGS. These could be of localized importance to reduce stream fine sediment levels;

Continue efforts such as road erosion proofing, improvements, and decommissioning throughout the basin to reduce sediment delivery to the Mattole River and its tributaries. CDFG stream surveys indicated Sulphur Creek and Sulphur Creek Tributary #1 have road sediment inventory and control as a top tier tributary improvement recommendation.

Encourage the use of appropriate Best Management Practices for all land use and development activities to minimize erosion and sediment delivery to streams. For example, low impact yarding systems should be used in timber harvest operations on steep and unstable slopes to reduce soil compaction, surface disturbance, and resultant sediment yield;

Based on the high incidence of unstable slopes in this subbasin, any future sub-division development proposals should be based on existing county-imposed forty acre minimum parcel sub-division ordinances;

Consider the nature and extent of naturally occurring unstable geologic terrain, landslides and landslide potential (especially Categories 4 and 5, page 89) when planning potential projects in the subbasin;

Riparian and Instream Habitat Improvement Activities

Maintain and enhance existing riparian cover. Use cost share programs and conservation easements as appropriate;

Landowners and managers in this subbasin should be encouraged to add more large organic debris and shelter structures in order to improve channel structure, channel function, habitat complexity, and habitat diversity for salmonids. Pool shelter has the lowest suitability for salmonids in Sulphur Creek Tributary #1, Conklin, and Green Ridge creeks;

Education, Research, and Monitoring Activities

Several years of monitoring summer water and air temperatures to detect trends using continuous, 24 hour monitoring thermographs should be done. Continue temperature monitoring efforts in the North Fork Mattole River, Sulphur Creek, and the Upper North Fork Mattole River, and expand efforts into other subbasin tributaries. Study the role of seeps and springs as cold water refugia in Oil and Rattlesnake creeks;

Establish monitoring stations and train local personnel to track in-channel sediment and aggraded reaches throughout the subbasin and especially in the lower reaches of the North Fork Mattole River and the Upper North Fork Mattole River;

Encourage more stream inventories and fishery surveys of tributaries within this subbasin;

  • In order to protect privacy while developing data, the possibility of training local landowners to survey their own streams and conduct salmonid population status surveys should be developed;