Stabilizing and Replanting Riparian Zones to Improve Fisheries

The Trinity River Task Force (TRTCC, 1989) has become increasingly interested in restoring riparian areas in the South Fork Trinity River basin. Cost-efficiency of riparian restoration projects can be quite good since a healthy riparian zone can provide steadily increasing benefits for streams and fish into the future. As stream side trees become re-established, their roots prevent erosion of valuable agricultural land and sedimentation of the stream (Cheney et al., 1990). Riparian trees help form a more well defined stream channel, which increases the stream's ability to route sediment. As fine sediments are scoured away and riparian trees provide large organic debris to the channel, increased channel complexity and greater pool depth will result.

Alder and willow have been used in most projects to restore a primary shade canopy. Coniferous species or big leaf maple can be planted in upslope areas or on terraces to develop a secondary over-story. The CCC has planted thousands of trees on many tributaries throughout the South Fork Trinity River basin (Table 10-1). On Tule Creek, the CCC planted trees and built one mile of fence to allow re-establishment of the riparian zone (Flosi, 1992).

Six Rivers National Forest is conducting a study to see if a large gravel bars in the lower South Fork Trinity River gorge can be revegetated with conifers (Chuck Glasgow, personal communication). In Grouse Creek, stream side landslides are being planted in an attempt to stabilize these features and reduce sediment input into the creek (Mike Furniss, personal communication). Matthews et al. (1990) conducted research to discover which plant species are hardy enough to colonize harsher upland sites in the Trinity River basin. In a related project on Grouse Creek, the USFS contracted with the CCC to plant various brush species and coniferous trees on unstable inner-gorge areas (Flosi, 1992). The CCC have also planted trees on smaller stream-side slides along the East Fork of the South Fork Trinity River (Lisa Heiki, personal communication), although lack of fencing and subsequent cattle grazing decreased project success.

Evaluating the Benefit of Fish Habitat Improvements

Although over $3 million have been spent on various South Fork Trinity River basin fish habitat improvement projects since 1985, evaluation of the effectiveness of restoration efforts to date is limited. Instream structures are somewhat experimental in nature and more evaluation needs to be done to discern whether continued heavy investment in such projects is wise. Some investments, such as improved fish passage, undoubtedly have pay back as fish colonize new habitats or return to areas that have been blocked. The benefit of in stream structures is less clear. The following discussion will address what we know about various salmon and steelhead habitat improvement projects both in the basin and in other areas that have been better studied.

Riparian Restoration Proven Effective

Dale (1990) thought that a CCC riparian planting project on Madden Creek had helped decrease the stream temperature substantially.The combination of log bank revetments in conjunction with willow planting on Barker Creek is thought to have greatly improved fish habitat (Tom Stokely, personal communication). The benefit of restoring riparian zones for fisheries, water quality, and soil conservation have been demonstrated in many other areas (Cheney et al., 1990).

Binns (1986) found a significant increase in native trout in a Wyoming stream as riparian zones were restored. Platts (1981,1982) also found that fish populations increased measurably in response to riparian improvements. Beschta et al. (1991) described additional benefits from riparian restoration such as a rise in the water table in response to channel adjustments, increased base flows, and improvements in water quality. Todd (1988) installed low cost electric fences to exclude cattle from riparian zones, and installed grade control structures, in Fish Hole Creek in the upper Klamath basin. He found that the forage base for grazing improved in upland areas away from restored riparian zones, as a result of a rise in the local water table.

Effectiveness of Instream Structures Remains Unclear

In the summer of 1992, Shasta-Trinity National Forest began a field survey to determine whether or not instream structures in various South Fork tributaries on USFS land have remained in place and functioned as intended. Prior to recent winter storms of 1992-93, a large majority of structures were still in place and most had created the intended changes in stream morphology (Ron Toroni, personal communication). However, most structures have been installed since 1986, and they have not been tested by high flows at the time of the inventory.

While structures installed in recent years seem to be used consistently by older age steelhead (Toroni, personal communication), fisheries studies show decreasing trends in total fish abundance in several streams that have been heavily treated with instream structures. Van Deventer (1992) compared population estimates and biomass of steelhead trout gathered from 1985-1990 in five South Fork Trinity River tributaries: Big Creek, upper Hayfork Creek, Rattlesnake Creek, Rusch Creek and upper Salt Creek. The fish population estimates were not specifically designed to gauge the effectiveness of channel treatments, but rather to provide an index of abundance in each drainage.

Van Deventer (1992) found that the standing crop of juvenile steelhead in most of these streams declined during the time of the study (Figure 10-1), although the average size of fish increased. Rusch Creek steelhead juvenile populations have shown little variability while Hayfork Creek showed a dramatic drop in 1987 and a gradual rebuilding since that time. Rattlesnake Creek showed a consistent declining trend in juvenile fish abundance from 1985-1989 with a slight rebound in 1990. Standing crops of juvenile salmonids on Big Creek have shown no clear trend but populations in 1989-1990 are down from 1986-1988. Population trends on Salt Creek are also difficult to discern but numbers of young steelhead have decreased substantially from their high in 1986. All of the streams under study have been treated with instream structures.


Figure 10-1. Estimated juvenile steelhead of all age classes, sampled by electroshocking in Big Creek, upper Hayfork Creek, Rusch Creek, Salt Creek and Rattlesnake Creek, 1985-1990. NOT AVAILABLE IN ELECTRONIC FORMAT


Because of the complex life history of salmon and steelhead, many factors can affect their survival and abundance (Fontaine, 1988). Short term natural variations in fish populations can mask any differences that might be caused by stream habitat changes (Platts and Nelson, 1988). However, it is also possible that Big Creek, Salt Creek and Rattlesnake Creek juvenile steelhead population decreases may be in response to reduction in spawning related to drought conditions during the time of the study.

An alternative hypothesis to explain the increase in size of steelhead and decrease in over-all abundance would be that older age steelhead are displacing younger age fish in these streams. The work of Olsen and West (1991) on Klamath River tributaries suggests that older age steelhead juveniles (1+ and 2+) strongly favor log covers. It is possible that intensive treatment with cover logs could decrease preferred habitat for younger steelhead juveniles by increasing niches for 1+ and 2+ steelhead.

Klamath Basin Cost/Benefit Study

Olsen and West (1990) evaluated structures in various Klamath River tributaries. They counted spawners and juvenile fish in the vicinity of ten structure types. Their evaluation did not involve pre-project and post-project comparisons at the treated site, but rather between project areas and untreated sites with similar habitat characteristics. They found more use by spawners and juvenile fish in treated areas, but whether there is a net increase in fish production as opposed to a shift in their use to treated areas is unknown.

Low cost structures such as "digger logs" were judged to have the best cost efficiency. Cover logs actually showed a decrease in use by young of the year steelhead and chinook salmon, although older age steelhead showed a preference for these structures. Weirs had a low cost/benefit ratio because of the substantial cost of construction. Olsen and West (1990) estimated the potential life of structures from 18 years, for a large weir, to 57 years, for a digger log, but they acknowledged that no structure in their study had yet experienced more than a two year recurrence interval storm.

Failure of Instream Structures a Common Problem

Frissell and Nawa (1992) described extensive damage or failure of instream structures in southwest Washington and southwest Oregon. Widespread problems occurred as a result of moderate flows during a storm event in February 1986, which was judged to be of 2-10 year recurrence interval. The authors considered a structure which was dislodged to have failed. Structures which were still in-place, but no longer functioning as intended, were classified as damaged. Mean failure rates for southern Oregon streams was 48% and mean failure/damage rates were 67%. In southwest Washington failure rate median was lower (6%) but the mean failure/damage rate was 46%.

Simple structures, such as cabled natural woody material, experienced much lower failure rates than complex structures such as log weirs which spanned the whole stream. There was also a positive correlation between increased channel width and structure failure rate. Frissell and Nawa (1992) concluded that the half life (the time elapsed when 50% of structures will be destroyed) was 10 years for southwest Oregon and 15 years for southwest Washington. Failure of structures was typically caused by major changes in stream morphology during flood events. Most structures were not designed to withstand the large organic debris and high volumes of sediment which are routed down the channel during storms.

Failure of instream structures was also documented in the Klamath basin during the February 1986 storm. Six Rivers National Forest had to replace and reinforce structures on Bluff, Camp and Red Cap Creeks as a result of damage from high flows (USFWS, 1991). In the South Fork Trinity River basin, one group of instream structures experienced problems similar to those described above. Large boulders (3-4' in diameter) were cabled together and placed in the channel of the upper South Fork Trinity River, just below the East Fork confluence in 1985. After the February 1986 storm event, these structures disappeared due to substantial aggradation at the site. They later re-emerged as material that had buried them was washed downstream (Dick Irizarry, personal communication).

Increased Fish Production Rarely Shown in Evaluations

The South Fork Trinity River basin study on production of juvenile salmonids (Van Deventer, 1992) is not the only study to show appreciable decreases in fish populations in areas treated with instream structures. Hamilton (1989) found a decrease in trout abundance in a northern California stream reach treated with boulder clusters. Fontaine (1988) found that structures in the Umpqua River failed to achieve increases in juvenile steelhead because warm water temperatures conferred a competitive advantage to redside shiners in the treated reaches.

The most extensive study to date of instream structural improvement and changes in juvenile salmonid production took place on Fish Creek in Oregon (Everest et al., 1988; Reeves et al., 1990). Downstream migrant traps allowed a complete count of juvenile coho salmon and steelhead juveniles emigrating from the basin. Baseline data was collected for several years before any fish habitat improvement projects were installed. When a total of 5% of all habitats in Fish Creek had been modified, no increases in coho salmon or steelhead trout were measured.

Subsequently, nearly 20% of the entire length of Fish Creek was treated, with an emphasis on creation of edgewater pools which favor coho salmon juveniles. A moderate gain in coho salmon juvenile production was achieved but no change in steelhead numbers was apparent (Reeves et al., 1990). Creating and enhancing side channel pools to increase rearing area for coho salmon also proved effective on the Clearwater River in Washington (Cedarholm et al., 1988). Ward and Slaney (1981), working in the Clackamas River, Oregon, found moderate or slight increases in fish population in response to fish habitat improvement projects. McCain (1992) found that boulder clusters in Hurdy Gurdy Creek (Smith River) attracted juvenile chinook salmon, but couldn't determine if they represented increases in total population or merely shifts in utilization from poorer quality habitat.

Transition in Restoration Strategies

"There are tremendous and persistent forces in [the]flow of water down steep channel gradients thatmove large and abundant material. Forces that can annually transport many tons of cobbles andboulders can make short work of any poorly designedand placed structures...Because fish densitiesin nutrient poor streams is low even under thebest conditions, it takes a large number ofenduring structures to make a significant difference...Some workers contend that habitat enhancementis rarely cost-effective and that we should placegreater emphasis on protecting stream habitatsthrough better management of hillslopes andriparian areas." Lisle (1988)

There has been an increasing awareness that fisheries restoration must take a watershed approach if it is to succeed (Orsborn and Anderson, 1986). The work of Frissell and Nawa (1992) demonstrated that we run a high risk of losing our investments in instream structures, even during low recurrence interval storm events, if we ignore sediment potential upslope and focus our attention only on improving stream channels. The costs and logistical problems associated with treating enough of a stream to make a significant difference in fish production may also be prohibitive. Chapter 10 continued.

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