Off-Channel/Floodplain

Floodplain restoration has been shown to be an effective technique for increasing rearing habitat for Chinook salmon and other species (Sommer et al. 2005). Fish that rear in floodplains have shown significant increases in growth compared to those rearing in mainstem habitats, likely due to favorable velocities, temperatures, and available food resources (Sommer et al. 2001, Sommer et al. 2005, Urabe et al. 2010).  Riverine species benefit from having access to floodplains for rearing and spawning and as refuge from high velocities (Jeffres et al. 2008).  New floodplain channels were associated with higher numbers of juvenile coho, cutthroat, and steelhead (Solazzi et al. 2000 as cited in Pess et al. 2005), and groundwater fed channels have supported increased numbers of chum, coho, pink, and sockeye salmon (Hall et al. 2000 as cited in Pess et al. 2005).

Common techniques for floodplain restoration and enhancement include levee removal or setback, reconnection of side-channels and floodplain channels, and creation of new floodplain channels.  These types of projects are targeted at increasing off-channel habitat and floodplain connection with mainstem channels, and range in size and scale from smaller side channel projects to floodplain reconnection and levee removal projects that are several miles long.  Techniques to reconnect floodplains are still in development (Cowx and Welcomme 1998 as cited in Pess et al. 2005, Pess et al. 2005) and additional study on the effectiveness of this project type is warranted.

This document details the monitoring design, procedures, and quality assurance steps necessary to document and report the effectiveness of Floodplain Enhancement Projects at the project site scale. This supports the Bonneville Power Administration’s (BPA) programmatic approach to project level Action Effectiveness Monitoring (AEM), as documented in “Action Effectiveness Monitoring of Tributary Habitat Improvement: A programmatic approach for the BPA Fish and Wildlife Program.” This is based on the Washington Salmon Recovery Funding Board (SRFB) protocol,–“Monitoring Effectiveness of Floodplain Enhancement Projects” (ID: 38) (https://www.monitoringmethods.org/Protocol/Details/38); and also draws heavily from the Scientific Protocol for Habitat Surveys within the Columbia Habitat Monitoring Program (CHaMP) (ID:806) (https://www.monitoringresources.org/Resources/Program/Detail/18); however, variations in the monitoring design and metrics collected required modification of the protocol.

Questions to be answered:

• Has the total habitat area, quantity of slow water habitat, and complexity of habitat increased as a result of the project?
• Has flood capacity increased?
• What is the level of water connection by season as intended by the project design? (e.g. designed to be connected at high water only, or also during low flows)
• What habitats are connected during each season?
• Have channel dynamics increased?
• Have juvenile salmon and steelhead numbers increased following restoration?  What is the presence and relative abundance of fish species and life stages by habitat type and season? How does fish use relate to limiting factors for given populations?
• Has abundance, diversity and ecological integrity of benthic invertebrates changed?  Does benthic invertebrate species composition indicate other ecological problems not addressed by the project?