Lower Gales Creek Enhancement Planning
Geomorphic Assessment • Technical Study

Table of Contents

Table of Contents
1.Introduction
2. Setting
3. Channel Conditions
4. Existing Conditions
5. Salmonid Restoration
6. References

5. Salmonid Restoration

5.1 Past Enhancement/Restoration Work

Historically, very little focus has been given to salmonids restoration on lower Gales Creek due to the perception that high summer water temperatures combined with low flow summer conditions have resulted in conditions that limit salmonids recovery. The restoration and/or enhancement work that has been completed through the study reach has focused primarily on reducing sources of fine sediment from bank erosion, implementing best management practices to control runoff of nutrients and sediment from adjacent agricultural lands, planting of riparian vegetation, and removal of non-native vegetation. Much of this work has been initiated by landowners with technical assistance from agencies such as the National Resource Conservation Service.

5.2 Evaluation of Recommended Restoration Sites

A primary objective of this study was to evaluate the feasibility of salmonids enhancement and restoration projects proposed in the Lower Gales Creek Habitat Enhancement Plan (LGCHEP) prepared in March of 2003 in relation to existing channel morphology and geomorphic trends. Though each of these projects would undoubtedly benefit salmonids if they were implemented, questions remained about their compatibility within the geomorphic setting and the likelihood of long-term project success given the dynamic nature and extensive bank instability of several of the reaches.

In the LGCHEP, projects were organized by reach. In most cases the recommended projects focused on riparian plantings and outreach programs with the community and landowners. Other project sites included recommendations to enhance instream habitat conditions such as large woody material installations or retrofitting of existing bank protection structures to include habitat enhancement elements. These projects were general in the sense that an entire reach was called out for treatment rather than specific project locations. Site specific projects were recommended based on discussions with landowners and often included bank protection work that could be integrated with habitat enhancement elements. Our analysis evaluates each of the instream projects and includes a discussion of the appropriateness of each of these projects and recommended modifications to improve their effectiveness. In Section 5.3 we provide a summary of the projects and provide additional project recommendations, where appropriate, to improve salmonid habitat.

Reach GL01 (Geomorphic Reach 2)

The LGCHEP recommended that large woody material be placed in this reach to increase instream complexity and provide refuge areas from high water temperatures. The initial focus of this work would be near the confluence of Clear Creek. The geomorphic analysis for this reach suggests that this area, especially near the confluence with Clear Creek, is depositional. The location of the low flow channel, bar deposits, and pools and riffles, are ephemeral in a strongly depositional environment. The location of these morphological features shifts during high flow events which may limit the success of installing large wood structures that are static. Given the presence of bridges and other infrastructure, large wood structures would need to be secured in order to gain landowner approval, meaning in some cases they could be left high and dry as the bar forms shift. There may be an opportunity to install large wood structures at the lower end of the reach or in areas where channel dynamics have been constrained by bank protection structures such as rock revetments. In that case, large wood structures could be integrated into these existing structures to improve localized scour and provide cover habitat for fish.

Reach GL02 (Geomorphic Reach 3)

Recommendations in GL02 are similar to those proposed for GL01. The focus would be on riparian revegatation and installation of large wood structures. Since this reach has been determined through the geomorphic assessment to be a transitional reach, large wood structures integrated into existing bank protection structures and/or strategically placed to encourage pool scour could be successful. Installation of large wood structures should be avoided in the vicinity of the bridge crossing through this reach given expected high velocities and the presence of easily erodible bedrock on the bed which would make it difficult to secure each element.

Reach GL03 (Geomorphic Reach 4)

No recommended actions.

Reach GL04 (Geomorphic Reach 4)

No recommended actions.

Reach GL05 (Geomorphic Reach 4)

This reach is located just upstream of the Roderick Road Bridge through a highly confined section of channel with extensive resistant bedrock exposures along both the bed and the banks. The LGCHEP recommends installation of large wood structures along this reach to enhance in-stream complexity. Given the confined nature of this reach, the lack of access, and bedrock exposures (implying high velocities), we do not recommend installing structures through this reach. It may be possible to anchor existing large wood that exists through the reach but bringing in new material may be difficult from an access standpoint.

Reach GL06 (Geomorphic Reach 4)

This reach is located downstream of the Roderick Road Bridge and consists of a straight section of channel that is transitional to the depositional reach downstream. The LGCHEP recommends installation of large wood structures through this reach as a way to enhance connectivity between the channel and floodplain. Conceptually, enhancing connectivity would be achieved by adding large wood as roughness, causing the stream to backwater under high flow conditions, thereby raising the water surface, which would increase the frequency at which water accesses the floodplain surface. Though there appears to be some floodplain through this reach, the channel is still fairly confined and much of the floodplain surface consists of low benches or terraces rather than abandoned secondary channels. Improved floodplain access should be one of the salmonid restoration goals but any recommended project should focus on reactivating an existing secondary channel rather than just improving floodplain surface connectivity. Secondary channels would provide the most benefit to salmonids as refuge habitat from high winter flows.

Reach GL07 (Geomorphic Reach 5)

This reach has been affected by recent channel incision and bank erosion. Sediment eroded from the banks has deposited as bars along this reach, exacerbating the channel widening phase. The LGCHEP recommends a combination of large wood structures and activation of a secondary channel in Reach GL07. Given the fact that this reach could provide high quality salmonid rearing habitat if enhancement measures were implemented, we support these proposals. In addition, where opportunities exist, floodplain areas should be created by cutting back vertical banks and creating benches located at the bankfull flood elevation.

The secondary channel identified as an opportunity on the left bank, appears to already have access with the primary channel. This interaction could be enhanced and habitat elements and large wood structures could be placed in the secondary channel to encourage its use as a refuge area for fish. In addition, large wood structures could be integrated into bank protection projects along the right bank. The bank protection projects would consist of toe protection with large wood and bank recontouring to reduce the slope angle. If space is available, a low bench could be built at the toe of the bank to provide additional protection and improve revegetation success.

Reach GL08 (Geomorphic Reach 5)

This reach consists of a relatively short section of channel with extensive bank erosion, primarily along the left bank. The prominent feature through this reach is a tortuous meander that is armored with rock along the outside of the bend. The point bar, which is now a terrace due to recent channel incision, constricts the flow through this meander bend. The result is a backwater condition during high flow conditions that has resulted in the formation of a large gravel bar at the confluence of Roderick Creek. As the gravel bar grows the point bar it forms is inducing severe erosion along the left bank, just upstream of the meander. The LGCHEP recommends enhancing the meander pattern upstream so as to slow the water, lengthen the flowpath and reduce the amount of energy directed at the eroding bank. If opportunities exist to increase the meander pattern upstream they should be pursued, but we feel that this approach will not reduce the amount of energy directed at the downstream bank. The problem lies with the channel constriction at the tortuous meander which has created a large, persistent bar deposit. The best approach to fixing this site would be to remove the constriction by cutting down the terrace to the bankfull elevation so it can act as floodplain. The existing steep bank could be cut back with large wood installed at the toe.

Reach GL09 (Geomorphic Reach 5)

The main recommendation along this reach is to reduce vehicle access and install large wood structures, where appropriate. Given the potential for this reach to support rearing habitat if water temperatures are reduced, we support this recommendation. Site access would be straightforward and the lack of high velocity conditions would allow for anchoring of any installed structures.

Reach GL10 (Geomorphic Reach 6)

The LGCHEP recommends installing large wood structures to increase in-stream channel complexity along this reach. Given the confined nature of this reach and the lack of a riparian corridor, any large wood structures installed along this reach should be integrated with bank recontouring and riparian revegetation.

5.3 Additional Restoration Recommendations

Figure 12 summarizes our review of the LGCHEC project recommendations and adds additional project opportunities based on our field visits. Figure 12 breaks the projects up into four categories and was meant to focus some of the recommendation provided in the LGCHEP. Consequently, some of the project recommendations may overlap:

Large wood structures: These projects consist of stand-alone installations of large wood to improve in-stream complexity, scour pools, and provide cover habitat.

Riparian plantings: These projects consist of riparian plantings to fill gaps in the riparian corridor. Riparian planting should focus on a mix of hardwoods and coniferous species so as to increase the diversity and provide future large wood to the channel.

Reactivate secondary channel: These projects consist of enhancing existing floodplain features to increase the frequency of primary and secondary channel interaction. Enhancements would be directed at both the primary channel and the secondary channel to encourage refuge areas for salmonids.

Bank recontouring: These projects are intended to reduce fine sediment erosion from steep banks. The techniques would vary depending on space available. Ideally the bank would be pulled back to provide a floodplain bench, the toe would be protected wilth large wood, the remaining bank would be angled to a 3:1 slope or less, and the site would be revegetated.

Additional projects, beyond what was reviewed from the LGCHEP and discussed in Section 5.2, include a recommended project in Reach 1 (Project #1) and a recommended project in Reach 4 (Project #6). Table 8 summarizes the objectives of each of the recommended projects.

Table 8: Potential habitat enhancement project opportunities for the Gales Creek study area. Project recommendations are based on field work, review of projects recommended in the LGCHEP, and a geomorphic evaluation of reach dynamics with regard to planform stability and sediment transport.

6. References

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