Rehabilitating Valley Floors to a Stage 0 Condition: A Synthesis of Opening Outcomes

Abstract

Degraded floodplains and valley floors are restored with the goal of enhancing habitat for native fish and aquatic-riparian biota and the protection or improvement of water quality. Recent years have seen a shift toward “process-based restoration” that is intended to reestablish compromised ecogeomorphic processes resulting from site- or watershed-scale degradation. One form of process-based restoration has developed in the Pacific Northwest, United States, that is intended to reconnect rivers to their floodplains by slowing down flows of sediment, water, and nutrients to encourage lateral and vertical connectivity at base flows, facilitating development of dynamic, self-forming, and self-sustaining river-wetland corridors. Synergies between applied practices and the theoretical work of Cluer and Thorne in 2014 have led this form of restoration to be referred to regionally as restoration to a Stage 0 condition. This approach to rehabilitation is valley scale, rendering traditional monitoring strategies that target single-thread channels inadequate to capture pre- and post-project site conditions, thus motivating the development of novel monitoring approaches. We present a specific definition of this new type of rehabilitation that was developed in collaborative workshops with practitioners of the approach. Further, we present an initial synthesis of results from monitoring activities that provide a foundation for understanding the effects of this approach of river rehabilitation on substrate composition, depth to groundwater, water temperature, macroinvertebrate richness and abundance, secondary macroinvertebrate production, vegetation conditions, wood loading and configuration, water inundation, flow velocity, modeled juvenile salmonid habitat, and aquatic biodiversity.

Macroinvertebrate assemblages from a stream-wetland complex: a case study with implications for assessing restored hydrologic functions

“…Regardless of the causal mechanisms, we regard the structure and function of the macroinvertebrate assemblages from the restored site during the early post-restoration years as indicative of a positive ecological lift from the restored valley, especially considering the potential impacts to higher consumers (Schindler & Smits, 2016 ). Flitcroft et al ( 2022 ) reached a conclusion similar to ours after their review of post-restoration monitoring studies from Stage 0 channels in the Pacific Northwest. More specifically, secondary production estimates indicated a greater capacity to support higher trophic levels during the first year following the restoration of the South Fork McKenzie River (Flitcroft et al, 2022 ).…”

“…These pre-settlement target conditions have been variously termed “stream-wetland complexes” or “stage 0 channels” (Cluer & Thorne, 2014 ; Kaushal et al, 2014 ), are typically anabranched, have frequently inundated floodplains, and have diverse but stable in-channel habitats. Stream-wetland complexes have been documented in many different environments (e.g., Collins et al, 2003 ; Harwood & Brown, 1993 ) and have served as the objective for stream restorations across the USA, including in the Pacific Northwest (e.g., Flitcroft et al, 2022 ), the Northeast (e.g., Goerman et al, 2013 ; Kaushal et al, 2014 ), and the Southeast (e.g., Parola & Hansen, 2011 ). A common goal for these restoration projects was to re-establish the connection between the stream and its floodplain, frequently leading to the formation of streamside wetlands.…”

“…Physical and biological data from the early post-restoration years following the restoration of stream-wetland complexes is limited and is just now beginning to appear in the published literature (Flitcroft et al, 2022 ). The objective of our study was to compare benthic macroinvertebrate assemblages from a recently restored stream-wetland complex to an unrestored, single-threaded channel with impaired hydrologic functions.…”

Rediscovering, reevaluating, and restoring Entiatqua: Identifying pre‐Anthropocene valleys in North Cascadia, USA

“…Vegetation assemblages are related to landforms identified in the GGL‐REM shown in Figure 2b, based on vegetation surveys and observations made in reaches of Whychus Creek, OR that have been restored to their pre‐disturbance condition, which is also known as Stage 0. The fully connected river‐wetland corridor would likely be perennially wetted due to greater inundation area and reduced depth to the alluvial aquifer, as has been observed at Whychus Creek and other locales where valley floor restoration has been implemented (Flitcroft et al, in press) Wetted area assumes the elimination of inferred anthropogenically‐triggered channelization and a water surface elevation at +0.1 m relative to the GGL. [Color figure can be viewed at wileyonlinelibrary.com]…”

Sampling-Based Approaches to Estimating Two-Dimensional Large Wood Area from UAS Imagery

“…Process-based restoration methods such as restoration to a Stage 0 condition that has been implemented in the Pacific Northwest often include addition of wood to the stream to jump start in-stream processes that depend on wood, such as macroinvertebrate life cycles [5] [6] [7]. Monitoring stream dynamics and wood retention within river restoration areas is important for assessing the restoration results and informing design for future restoration projects.…”