Ecohydraulics Research Group, University of Idaho,

800 Park Blvd., Boise, ID 83712, USA

phone: (208) 364 4090; Fax: (208) 387 1246, E-mail: muski@uidaho.edu

Kerry Overton and Bruce Rieman

US Forest Service, Rocky Mountain Research Station, Idaho, USA.

Abstract: Strategies for river restoration or enhancement have evolved rapidly during the past three decades and are usually undertaken to correct adverse impacts resulting from damaging management activities. Initial approaches concentrated on piece-meal restoration of local habitat, frequently undertaken without due regard to hydraulics, geomorphology, sediment transport characteristics or regional ecological linkages. More recent strategies have shown that adverse impacts to the aquatic ecosystem induced by watershed scale changes often require remedial management actions at the watershed scale to address the issues in a sustainable manner. It has also been recognized that the key to many enhancement projects depends upon our ability to restore the physical processes that create and maintain a healthy river system. Development of a sustainable solution often requires a long-term strategy, since some actions may take years to implement and this may be followed by another extensive interval before downstream benefits are achieved. Peer review groups (for example, the Independent Scientific Review Panel (ISRP) within the Columbia Basin) have raised poignant questions about how limited mitigation funds should be invested. In particular, how should potential enhancement activities be prioritized for the greatest benefit of the ecological resources? Secondly, can the ecological benefits of local restoration or enhancement projects be quantitatively proven at the local and watershed scale? A methodology for a decision framework for the selection of sites, examples of specific river restoration strategies, establishment of performance criteria for quantifying the performance at the local and watershed scales is outlined.

 

Keywords: aquatic system review, upper salmon subbasin, environmental impact assessment

Extensive attention has been focused on the restoration or enhancement of river systems during the past two decades. There are very few opportunities to undertake true restoration of a river system to some historical condition. The physical characteristics of the channel may be re-created in the short-term, but the channel will then adjust to current land use, prevailing climate and physical conditions within the watershed. These physical conditions include rainfall-runoff characteristics, sediment delivery, linkages to groundwater and storage functions of floodplains or wetlands. These processes will probably have been altered irretrievably. Most projects are therefore enhancement projects with a goal of assisting the channel to achieve a level of dynamic equilibrium with the current or expected watershed processes. It is then assumed that the prevailing conditions and rates of system change will be close to the conditions that the ecosystem has evolved under. These conditions should then provide the greatest opportunity for the recovery of habitat, vegetation and aquatic species.

As forensic studies of the performance or river and estuarine systems have become available in the past few years, the need for watershed level assessment has become apparent. For example, the intended benefits of a restoration project might not be achieved if the biostabilization is engulfed by a debris flow from upstream, or if a larger pattern of channel degradation undermines stabilized banks. Examples of restoration failures that did not account for physical processes or the larger watershed-scale system appear extensively in the literature. Expenditure for these restoration activities runs into the hundreds of millions of dollars per year in the Western States, but this is insufficient to begin to address all the diverse needs. This poses a dilemma for resource agencies and institutions with mitigation responsibilities. How should restoration activities and specific sites be prioritized scientifically– particularly in a political and social arena? Secondly, how can the benefit of each specific enhancement be proven at the site and watershed scale. This is of particular importance if the restoration plan is part of an anadromous fish recovery where the fish population is subject to natural variability and external factors such as dams obstructing migration, fishing and predators.

(1) When a sub-basin is identified as critical, how should restoration activities be prioritized?

(2) How can the ecological benefit to various indicator species be quantified in the local region of the restoration?

(3) How can the ecological benefits be demonstrated at the watershed scale?

This paper describes a methodology for aquatic systems review that attempts to provide a preliminary approach to addressing the concerns of ISRP. The question of scale is important, and the methodology considers the sub-basin scale evaluated by EDT down to 6^th field HUCs and local channel reaches. Landscape scales included in this analysis are:

(1) Subbasin: 4^th-field Hydrologic Unit Code (HUC) averages 200,000 hectares

(2) Watershed: 5^th-field HUC ranges from 20 – 40,000 hectares

(3) Subwatershed: 6^th-field HUC ranges from 5 – 15,000 hectares

(4) Stream Reach: Length equals 10 – 100 times the average channel width (the usual scale for habitat restoration activities).

The natural condition database has been compiled for stream channels within the Salmon River Basin, Idaho, that represent the natural state (structure and pattern) of streams only influenced by natural disturbances. Using these data, frequency distributions (relative and cumulative frequencies) can be graphed to display the range and distribution of natural variability for percent bank stability, percent bank undercut, water temperature, width-to-depth ratio, width-to-max depth ratio, and percent surface fines. This database is used to develop criteria that represent the natural or potential conditions that would be available in a stream that was not habitat limited. Comparison with existing conditions allows the level of habitat degradation to be quantified and the extent of enhancement required to return a reach to full or partial potential.

The review process comprises fifteen steps:

Step 1. Identify External Factors that Influence the Ecological Health of the Subbasin

Step 2. Develop Specific Objectives for Enhancement/Restoration

Step 3. Identify Subbasin Characteristics

Step 4. Identify Current and Historical Species Distribution

Step 5. Determine Species Status for Spawning and Rearing Subpopulations

Step 6. Identify Stronghold Watersheds

Step 7. Delineate Conservation and Restoration Watershed Areas

a) Conservation areas

b) Restoration areas

c) Marginal areas

Step 8. Develop Conservation and Restoration Plans

Step 9. Perform Detailed Analysis on High Priority Watersheds

Step 10. Review Recommendations and Prioritize Restoration Areas

Step 11. Plan, Design, and Implement Specific Restoration Actions

Step 12. Establish Performance criteria

Step 13. Monitoring and Evaluation

Step 14. Operations and Maintenance

Step 15. Feedback Loop to Step 1

The analysis of fish populations, the risk of extinction and the recovery potential provides necessary knowledge, but insufficient information to prioritize restoration actions. Additional categories include broader environmental considerations, socio-political issues and project feasibility (Figure 1 and Figure 2).

In the case of the Upper Salmon Basin, the Battelle method for environmental assessment (Dee et al., 1973; ?imi?, 1993; DHI, 1998) is being modified for prioritizing these projects. An example of result of prioritization process is shown in Figure 2.

The analyses listed above enables the various actions to be selected, but is it possible to demonstrate benefits on a wider scale? Two indicator variables are the subject of current studies- sediment and temperature. Two sites in the Upper Salmon River subbasin have been selected and established as longterm monitoring sites (Figure 3).

The Yankee Fork site has been subject to extensive dredging and mining activities resulting in an artificially straightened and deepened channel. The 12-mile reach on the Salmon River is about 50 river miles downstream and is experiencing major channel instability. If the Yankee Fork reach is enhanced - for example the floodplain function and riparian vegetation cover restored, will the reduction in temperature and the reduction in the delivery of fine sediment at the 12-mile reach be detectable, predictable and significant? If these changes are measurable and can be simulated, what extent of restoration activities must be completed to reduce the temperature and fines on the bed to levels recommended by federal guidelines?

Fig. 1 Example of elements considered in a prioritization methodology

The effects of fine sediments on salmonids varies with the life history stage of concern. Intrusion of fine sediment in gravel nests (redds) can reduce the egg-to-fry survival by limiting the intergravel dissolved oxygen levels essential for embryonic development or by plugging the interstitial spaces which prevents fry emergence. Fine sediment particles in streams can also limit the feeding efficiency of juvenile salmon and trout, since they rely on visual cues to find and capture prey during the early life stage as foraging fish.

Both chronic and storm-event sources of fine sediment can be exacerbated by anthropogenic activities. This includes elimination of natural floodplain function, removal of riparian vegetation, accelerated bank erosion, seeps and springs, gravel or dirt road surface erosion, shallow rapid landslides in small, steep headwater streams; bank trampling by livestock, failure of livestock manure containment lagoons, soil erosion from tilled agricultural crop lands, irrigation return flows. Biostabilization of the channel and adjacent slopes will reduce the delivery of fine sediment and a restored wetlands in the floodplain is predicted to capture a significant percentage of the suspended sediment load under flood flows. The reduction in the delivery of fine sediments at the twelve mile reach will be simulated by hydraulic models and validated by field observation.

Salmonids have evolved in a climate regime and stream and lake habitats which provide cool temperatures year around. Elevated temperatures hinder salmonids by increasing food requirements, increasing adverse interactions with toxics, and increasing incidence of disease. At cold temperatures, fish cannot avail themselves of the energy in their food because their metabolic rate is too slow and inefficient. Table 1 summarizes temperature requirements for one salmonid species in region.

Table 1  Temperature requirements for Chinook Salmon (independent scientific group, 1996)

The restoration of the Yankee Fork will create a narrower and deeper low-flow channel as well as providing shade from the riparian vegetation canopy. The temperature regime at both sites is being monitored and the downstream extent of reduced temperature through the Yankee Fork reach will be both monitored and simulated by computer model.

The Aquatic Systems Review is typical of the complex questions being posed to ecosystem managers. To begin to address these issues in a defensible and transparent manner, an interdisciplinary approach is required. Further, innovative tools that are understandable to people with a broad range of backgrounds and levels of scientific expertise are essential in translating projects from the design to implementation stages. This is the type of problem originally envisioned by Abbott in the late 1980s that resulted in the evolution of the field hydroinformatics. A preliminary approach is being tested on the Upper Salmon Basin.

This initiative is being funded by several sources including the US Forest Service, Bonneville Power Administration Fish and Wildlife Mitigation Program, and the National Science Foundation award BES-9874754 (Ecohydraulics: simulation of physical processes in river ecosystem management).

Danish Hydraulic Institute, 1998. User manual for MIKE Impact.

Dee, N. et al., 1973. Environmental Evaluation System for Water Resources Planning. Final Report for Water Resources Planning, Bureau of Reclamation, U.S. Department of the Interior. Battelle Laboratories, Columbus.

Independent Scientific Group, 1996. Return to the river: restoration of salmonid fishes in the Columbia River ecosystem. Northwest Power Planning Council. 567p.

Lestelle, L.C., L.E. Mobrand, J.A. Lichatowich and T.S. Vogel, 1996. Applied Ecosystem Analysis – A Primer. The Ecosystem Diagnosis and Treatment Method. Bonneville Power Adminstration, Project 9404600. 95p plus appendices.

Northwest Power Planning Council, 2000. Renewing the NWPPC Fish and Wildlife Program: Multi Species Framework Project. NWPPC, Portland, Oregon. 24p.

Simic, S., 1993. A Decision Support for Environmental Assessment. M.Sc. thesis HH367, IHE, Delft.