Incidence and Causes of Physical Failure of Artificial Habitat Structures in Streams of Western Oregon and Washington

Abstract

In recent years an increasing share of fishery management resources has been committed to alteration offish habitat with artificial stream structures. We evaluated rates and causes of physical impairment or failure for 161 fish habitat structures in 15 streams in southwest Oregon and southwest Washington, following a flood of a magnitude that recurs every 2–10 years. The incidence of functional impairment and outright failure varied widely among streams; the median failure rate was 18.5% and the median damage rate (impairment plus failure) was 60%. Modes of failure were diverse and bore no simple relationship to structure design. Damage was frequent in low‐gradient stream segments and widespread in streams with signs of recent watershed disturbance, high sediment loads, and unstable channels. Comparison of estimated 5–10‐year damage rates from 46 projects throughout western Oregon and southwest Washington showed high but variable rates (median, 14%; range, 0–100%) in regions where peak discharge at 10‐year recurrence intervals has exceeded 1.0 m3·s–1·km–2. Results suggest that commonly prescribed structural modifications often are inappropriate and counterproductive in streams with high or elevated sediment loads, high peak flows, or highly erodible bank materials. Restoration of fourth‐order and larger alluvial valley streams, which have the greatest potential for fish production in the Pacific Northwest, will require reestablishment of natural watershed and riparian processes over the long term.

Developing a broader scientific foundation for river restoration: Columbia River food webs

“…For example, field experiments in the US Pacific Northwest have shown that trophic manipulations (e.g., nutrient additions or salmon carcass introductions) that boost the abundance of potential prey organisms also boost subsequent fish growth (7)(8)(9)(10). In contrast, restoration of physical habitats by creating pools or adding structures yields ambiguous evidence that such efforts increase subsequent fish abundance and biomass (11)(12)(13)(14)(15)(16)(17). Although it may be premature to conclude from these studies that food availability and species interactions are more limiting to fish than the quality or quantity of the physical habitat, evidence is mounting that many habitat restoration activities are not always as effective in meeting stated goals and objectives as originally anticipated.…”

Libby Mitigation Program, 2007 Annual Progress Report: Mitigation for the Construction and Operation of Libby Dam.

“…Most of the stream restoration activities that others report either the successes Binns and Remmick 1994;Burgess and Bider 1980;Hunt 1976;House andBoehne 1985 and or failures (Frissell and Nawa 1992;Pattenden et al 1998;Hamilton 1989) typically implemented what we would consider habitat enhancement activities rather than stream channel reconstruction as was the case with each of the projects we completed. Frissell and Nawa (1992) and Pattenden et al (1998) agreed that the risk of failure of stream restoration activities is highest in streams with recent watershed disturbance, high instream sediment budgets, and unstable stream channels.…”

“…Grave, Libby, Young and Therriault creeks are good examples of streams that fit both sets of circumstances. Frissell and Nawa (1992) and Pattenden et al (1998) also noted that when failure or impairment occurred in stream restoration projects, it generally was a result of watershed driven aspects of stream channel dynamics rather than internal structural failures, and that rain on snow events produced some of the highest incidences of structure failure. This was certainly the case with the three restoration projects on Libby Creek in November 2006, in which case a rain on snow event occurred throughout the watershed.…”

A geomorphic assessment to inform strategic stream restoration planning in the Middle Fork John Day Watershed, Oregon, USA

“…For instance, the U.S. Pacific Northwest is replete with examples of large wood placement projects that aimed to enhance salmonid habitat but failed due to a lack of consideration of local geomorphic conditions and watershed hydrology (e.g. Frissell & Nawa, 1992). By formally considering a reach's natural behavior, trajectory, and capacity for adjustment, such assessments can help restoration practitioners to 'work with nature' (Brierley, Fryirs, Outhet, & Massey, 2002) leading to longer lasting and more appropriately sited restoration treatments.…”