Key Findings

Dewatered stream channels are a serious problem during summer low flow periods in the mainstem Mattole River and select reaches of many tributaries;

No systematic, scientific studies have examined the size or health of salmonid populations in the Southern Subbasin. However, historical accounts and stream surveys conducted in the 1960s by CDFG indicate that the Southern Subbasin supported populations of Chinook salmon, coho salmon, and steelhead trout. Recent biological stream surveys indicate the presence of steelhead trout and coho salmon throughout the Southern Subbasin. This subbasin supports coho salmon in more tributaries than the other Mattole subbasins. Low salmonid populations throughout the Mattole Basin indicate that salmonid populations in the Southern Subbasin are also likely to be depressed at this time.

Erosion/Sediment
As indicated by the Potential Stream Sediment Production EMDS, potential fine sediment delivery to streams due to road runoff is high in the Southern Subbasin. Although there are few roads on unstable slopes, there are many roads positioned low on hill slopes and many road crossings of streams throughout the Bridge Creek and Thompson Creek Planning Watersheds. The types and variety of macroinvertebrates indicate fair to good, good, or good to excellent instream conditions. Additionally, amphibians sensitive to fine sediment were present in several stream reaches surveyed in this subbasin;

Riparian/Water Temperature
Available data suggest that summer water temperatures support rearing juvenile salmonid populations in most reaches of most streams with summer flow in this subbasin;

Based upon 26 miles of surveyed stream habitat in the past 10 years, the Southern Subbasin is considered to contain some of the best salmonid habitat in the Mattole Basin. The utility of this good habitat for salmonids is compromised because of summer de-watering of the upper mainstem reach and many subbasin tributaries;

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

Most creeks in this subbasin are considered good refugia;

The geologic conditions in the Southern Subbasin are the most uniform and stable in the Mattole Basin. Nearly all the hillside areas are underlain by hard terrain. Correspondingly, this subbasin has the lowest density of mapped landslides, and stream channels within the Mattole Basin, and is the least impacted by features indicative of excess sediment production, transport and storage in the basin;

Redwood stands occur in this subbasin because of favorable conditions, including summer fog. As a result of past timber harvest and conversion activities, over 60% of the Southern Subbasin is occupied by small diameter (twelve to twenty-four inches diameter at breast height) forest stands. Another 22% is in forest stands greater than twenty-four inches. Industrial timberlands on the eastern side of the subbasin have been intensively managed in the past decade and are characterized by young, even-aged conifer stands;

This is the most densely populated area in the Mattole Basin. Many of the landowners have conservation easements as a part of Sanctuary Forest. Roads, abandoned after early timber harvest activities, are being upgraded and stormproofed by landowners. Many of these roads are now used as residential and parcel access roads and are located near streams.

Recommendations

Encourage reducing the unnecessary and wasteful use of water to improve summer stream surface flows and fish habitat;

Increase the use of water storage and catchment systems that collect rainwater in the winter for use in the drier summer season;

Support local efforts to educate landowners about water storage and catchment systems, and to find ways to subsidize development of these systems;

Ensure that this high quality habitat is protected from degradation. The highest stream reach conditions as evaluated by the stream reach EMDS and refugia analysis were found in the Bridge, West Fork Bridge, South Fork West Fork Bridge, South Fork of Vanauken, Mill (RM 56.2), Stanley, Baker, Thompson, Yew, and Lost Man creeks, the Upper Mattole River, and Lost Man Creek Tributary;

Improve the culvert on Stanley Creek that is blocking juvenile salmonids from accessing high quality rearing habitat;

Establish monitoring stations and train local personnel to track in-channel sediment and aggraded reaches throughout the subbasin and especially in Bridge and Thompson creeks;

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;

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;

Expand road assessment efforts because of the potential for further sediment delivery from active and abandoned roads, many of which are in close proximity to stream channels;

Continue efforts such as road improvements, and decommissioning throughout this subbasin to reduce sediment delivery to the Mattole River and its tributaries. CDFG stream surveys indicated South Fork Vanauken Creek, the Upper Mattole River, Stanley Creek, Thompson Creek, and Yew Creek have road sediment inventory and control as a top tier tributary recommendation. In 2002, road erosion assessments and road erosion control projects were underway in the upper Mattole Basin;

Further study of timberland herbicide use is recommended;

Follow the procedures and guidelines outlined by NCRWQCB to protect water quality from ground applications of pesticides;

A cooperative salmonid rearing facility exists in the headwaters, operated since 1982 by the Mattole Salmon Group. This operation has been successful and should be continued on an as needed basis in order to supplement wild populations of Chinook salmon;

Initiate a training program for local landowners to survey their own streams and monitor salmonid populations. This will provide important data and protect privacy;

Monitor summer water and air temperatures to detect trends using continuous 24 hour monitoring thermographs. Continue temperature monitoring efforts in Bridge, Vanauken, Baker, Yew, Thompson, Helen Barnum, Lost Man, Dream Stream, and Ancestor creeks, and expand efforts into other subbasin tributaries.