Past land management in the South Fork Trinity River has had a significant effect on present day watershed and stream conditions. The most widespread type of land use has been timber harvesting and the related construction of thousands of miles of forest roads. Erosion and sedimentation impacts from forestry operations, in concert with the effects of large floods, are thought to have caused significant reductions in fish habitat and fish populations over the last four decades.
The South Fork Trinity River is the largest free-flowing Wild and Scenic River in California. Most of the 950 mi2 watershed is managed by the U.S Forest Service (Shasta-Trinity National Forests and Six Rivers National Forest).
Approximately 20% of the South Fork Trinity River watershed (192 mi2) is privately owned (CDWR, 1979; Irizarry, et. al., 1985). Private lands are largely distributed in two locations, with differing land use patterns in each area (Figure 5-1). The Hayfork watershed has a large area of private holdings encompassing the town of Hayfork and agricultural lands throughout Hayfork Valley. A second large "block" of private land is found on the east facing slope of South Fork Mountain. This land is almost entirely timbered and dedicated to commercial forestry operations by a relatively small number of large timberland owners.Figure 5-1. Private and Federal ownership in the south Fork Trinity River basin.
South Fork Trinity River Timber Harvesting History
Prior to the commencement of serious logging in the 1940s, 80% of the South Fork Trinity River basin was covered in fir and pine forest, with 20% in brush, grass and rock. Since that time, human impact to the basin has been substantial. By 1977, 52% of the watershed had already been logged and an additional 4% of the old growth had been burned. Total road length visible on U-2 photos was 3,456 miles, 92% of which were associated with timber harvests (CDWR, 1979). An undetermined, but substantial, amount of additional acreage has been affected by logging, road construction and wildfires in the basin since the 1977 inventory.
Table 5-1 outlines the status of forested lands in 34 watersheds of the South Fork Trinity River as of 1977. No more recent land use inventory has been assembled to track harvesting and road construction since the mid-1970s. It is clear that considerable timber removal (and associated road construction) occurred in many basins both before and following the 1964 storm and flood. The amount of erosion and sedimentation originating from logged and roaded lands was often a direct consequence of the timing of land use in relation to major storms in these sub-watersheds
Table 5-1. Logging history for selected South Fork Trinity River tributary
basins covering 50% of the total watershed area (CDWR, 1979).
Pre-1965 logging Pre-1977 logging
Tributary Basin Area
Basin (mi2)
mi2 (%) mi2 (%)
Madden Creek 24.3 4.4 (18) 9.8 (40)
Mosquito Creek 15.5 1.1 (7) 5.6 (36)
Surprise Creek 1.1 0.2 (18) 0.2 (18)
Hell's Half Acre 2.0 0.0 (0) 1.1 (55)
Creek
Cow Creek 5.4 0.7 (13) 1.5 (26)
White Oak Creek 4.3 1.2 (28) 3.6 (82)
Grouse Creek 58.7 7.6 (13) 26.2 (45)
Bear Creek 7.2 1.7 (24) 5.1 (71)
Eltapom Creek 20.1 5.7 (28) 10.2 (51)
Corral Creek 37.6 12.1 (32) 22.4 (60)
Big Creek 28.0 8.5 (30) 12.6 (45)
Barker Creek 10.7 2.2 (21) 5.9 (55)
Duncan and Carr 28.6 unk 12.9 (45)
Creeks
Lucy Gulch and Big 8.7 1.5 (17) 4.3 (50)
Creek
Mill Creek 2.4 0.8 (34) 1.7 (73)
Kerlin Creek 4.4 1.6 (37) 3.2 (74)
Pelletreau 12.4 9.2 (74) 10.0 (81)
Cold Springs Creek 2.8 1.0 (36) 1.6 (57)
Hitchcock Creek 1.4 0.5 (36) 0.8 (58)
Sulpher Glade Creek 4.5 2.4 (53) 2.9 (65)
Butter Creek 38.0 18.1 (47) 26.8 (70)
East Fork Hayfork 26.5 7.9 (30) 7.9 (30)
Creek
Goods Creek 5.6 2.4 (43) 5.5 (98)
Swift Creek 1.2 0.2 (20) 0.5 (45)
Clear Creek 1.2 0.0 (0) 0.3 (30)
Granite Canyon Creek 1.0 0.0 (0) 0.2 (23)
Glen Creek 2.6 0.0 (0) 0.7 (27)
Collins Creek 1.4 0.0 (0) 0.6 (42)
Farley Creek 2.5 0.0 (0) 0.9 (35)
Marie Creek 1.5 0.2 (13) 0.2 (13)
Cable Creek 4.2 0.9 (21) 0.9 (21)
Bierce Creek 6.3 0.6 (10) 5.4 (87)
Rattlesnake Creek 48.8 41.7 (85) 44.2 (91)
East Fork South Fork 26.1 2.4 (9) 15.5 (60)
and Dark Canyon
Totals 446.8 136.9 (31) 251.4 (56)
Federal lands within the central portion of the South Fork Trinity River watershed were the site of intensive selective logging in the 1950s, under a concept called "unit area control." Much of this area included gentler, upland areas extending from Rattlesnake Creek to Wildwood to Philpot Creek. Management practices were poor, including skid trails and landings located in drainages, and high road densities (USFS, 1990i). Clearcut logging did not commence on National Forest lands in the South Fork Trinity River watershed until the 1970s. Under this silvicultural system, the Forest Service implemented a patchcut grid on much of their ownership. Oversight and control of plan layout, logging techniques and road building practices was minimal during this early period of land use (Veevaert, personal communication).
In the lower basin, timber harvesting began on the upland private holdings on South Fork Mountain in the late 1950s. From 1957-1960 logging on private lands resulted in removal of timber from up to 47% of some watersheds (Table 5-1). Most of the intensive, harvesting of timber from private lands on South Fork mountain was conducted in the 1950's, 1960's and 1970's. Nearly all yarding was done by tractors, resulting in dense networks of roads, landings and skid trails. Road densities ranged from 7.4 to 11.2 miles/mi2, and occupied from 5.8 to 7.8 percent of the area (Haskins, 1983).
In the last decade, there has been reentry to log remaining timber on many private lands on South Fork Mountain (Veevaert, personal communication). The future rate and timing of harvesting on private lands will be naturally limited by the comparatively low volume of timber which remains. To our knowledge, there is no inventory of the remaining volumes and distribution of privately owned timber in the sub-watersheds of South Fork Mountain.
"Human impact on the watershed has been significant and has contributed to the degradation of salmonid habitat in the river" (CDWR, 1982). Logging and road building has likely had the greatest effect on the South Fork Trinity River, while agricultural activities and past mining have strongly influenced conditions in the Hayfork Creek watershed (Irizarry, et. al., 1985).
Some geologic terrains in the watershed appear to be much more resistant or insensitive to timber management than others. These include Hayfork terrane and parts of the Rattlesnake Creek terrane (Figures 4-1 and 4-2). It is thought that properly conducted and controlled timber harvesting in about 2/3 of the watershed does not appear to have serious, long-term consequences (CDWR, 1982). Studies have suggested that over most of the basin, geologically sensitive terrain is not common, and human activities do not cause excessive stream turbidity. "In these more stable areas, timber management can likely be [conducted] on a long-term sustained yield basis" (CDWR, 1982).
In contrast, the most sensitive areas in the watershed occur along the eastern slope of South Fork Mountain and along the oversteepened inner gorge slopes of the South Fork Trinity River and its tributaries (CDWR, 1979). Here, serious on-site and off-site erosional impacts have resulted from harvesting and road building (CDWR, 1982). In fact, nearly 90% of the 40 mile long eastern slope of South Fork Mountain ridge, totalling 100 mi2 of land, is underlain by the highly unstable South Fork Mountain schist (Haskins, et. al., 1980). This terrain is one of the most landslide prone and environmentally sensitive areas in Shasta-Trinity National Forest (Haskins and others, 1980).
Most of the private timber holdings on South Fork mountain occur on what has been classified as highly sensitive terrain (Haskins, 1983). Past timber harvest and related land management activities have had a substantial effect on sediment yield to the lower South Fork Trinity River and its tributaries, and created long lasting impacts to downstream fish habitat (Haskins and Irizarry, 1988)(Plate 2). Cutting of even the isolated, remnant stands of timber on steep inner gorge and peripheral zone locations could have a significant impact on future sediment yield from these watersheds (Haskins and others, 1980).
The effect of forestry operations on erosion and sedimentation in the South Fork Trinity River and it tributaries first received serious attention following the 1964 storm and flood when large segments of the landscape along South Fork Mountain experienced accelerated landsliding and erosion, especially on the flanks of South Fork Mountain (MacCleery, 1974; Kojan, 1974, 1976; CDWR, 1979). MacCleery (1974) found a direct link between past logging (the percent of the watershed logged) and the degree of channel damage following the 1964 flood. Watersheds in which less than 30% of the timber had been logged suffered significantly less damage than the more heavily managed basins.
Severe damage occurred to areas which had been extensively logged before the 1964 flood. For example, South Fork Mountain tributary basins logged more than 30% suffered severe to very severe damage (CDWR, 1979). None of the extensive stream channel damage which occurred on the logged watersheds west of the South Fork Trinity River were duplicated on the unlogged eastern slopes of the basin (MacCleery, 1974; CDWR, 1979). Large delta deposits at the mouths of Pelletreau, Grouse, Cold Springs and Johnson Creeks are indicators of the sensitivity of the South Fork Mountain terrain, as compared to the minor deposits at the mouth of Hayfork, Eltapom and other streams draining less sensitive landscape areas east of the South Fork Trinity River (CDWR, 1979).
MacCleery's (1974) and Kojan's (1974; 1976) pioneering work and observations on the causes, locations and associations of logging, road building and landscape "sensitivity" on South Fork Mountain slopes eventually lead to the development of a cumulative effect methodology for analyzing forest lands management on the National Forest (Haskins, 1983). From this analysis, the U.S. Forest Service has developed management alternatives and land use "zoning" that take into account the sensitivity of each of Kojan's (1974; 1976) landslide hazard zones (Haskins, et. al., 1980). Some of the most sensitive and unstable lands are no longer managed for timber production (Haskins, personal communication, 1992) and these have been removed from the timber base (Veevaert, personal communication, 1992).
Three management factors were found to contribute significantly to the initiation of debris torrents and large scale inner gorge mass wasting on South Fork Mountain (Haskins, 1981). Each of these has been addressed in revised forest practices on federal lands. These factors include:
1. poorly designed stream crossings,
2. clearcutting and tractor logging within the inner gorge zone, and
3. harvest levels in excess of what the watersheds can withstand.
Many stream crossings were poorly designed and too large in number. The use of log fills, log culverts, undersized culverts, poor inlet and outlet structures and excessive sidecasting lead to many stream crossing failures where logging had already been extensive. On private lands, numerous log crossings still exist and many stream crossings are found on roads which have been abandoned for decades. These will eventually fail and wash out, or result in gullies or landslides caused by stream diversions. In addition, many stream crossings which were constructed in the past have a high failure potential since they do not meet current CDF design standards of being capable of passing the 50-year flood discharge.
The vast majority of landslide generated sediment resulting from past management activities originated in valley inner gorges (Haskins, 1981). An extensive inner gorge extends along the main stem of the South Fork Trinity River itself, but tributary inner gorges also extend far upslope into channels as small as second order. The risk of initiating landsliding by management in and near these inner gorges is high. Tractor clearcutting of the inner gorge area, the loss of root strength and great surface disturbance are all factors which contributed to inner gorge debris sliding and avalanching. In areas underlain by South Fork Mountain schist, debris slides and avalanches occur on slopes over 50%, generally along the margins of these incised drainages (Haskins, 1981).
Vegetation plays an important role in stabilizing inner gorge slopes. Once vegetation is removed from the base of the slope, by landsliding or harvest, subsequent landsliding un-weights and destabilizes upslope areas. Debris torrents in steep channels, triggered by excessive harvesting and poor roading practices, cause severe channel damage which propagates into upslope areas. Through scouring miles of channels, many square miles of upslope areas can be destabilized for decades as the hillslope readjusts to a new equilibrium profile (Haskins, 1981). This occurred in many South Fork Mountain tributaries during and following the 1964 flood. Chapter 5 continued