New Research article: Full floodplain connectivity: Realising opportunities for ‘Stage 0’ river restoration

Date: April 2024

Continued declines in freshwater biodiversity and the challenges of climate change are creating greater interest in river restoration projects. Increasing recognition of the interaction between biological, geomorphological and hydrological processes has led to the development of ‘Stage 0’ river restoration. Stage 0 reaches are typically multi-thread anabranching systems connected to the floodplain and its ecosystems. It is suggested that the defining characteristic of Stage 0 conditions is that of connectivity (longitudinal, lateral and vertical) at base flows. The methods or mechanisms that can re-create such reaches are described, namely valley floor reset, beaver activity, beaver dam analogues and the use of large wood in the channel and floodplain. The scope for wider adoption of Stage 0 is then discussed and recommendations for expanding this approach across temperate regions with a long history of river modification and higher population densities are presented.

A new paper has been published studying the effects of Stage Zero on Lampreys.

January 2024

Abstract: We examined occupancy and density of larval lampreys (Entosphenus tridentatus and Lampetra spp.) in two rivers in Oregon (USA) restored to a Stage 0 condition 1–5 years prior, using a multiscale occupancy model and a zero-inflated Poisson mixture model. We sampled lampreys using backpack electrofishing in randomly distributed, paired, 1-m2 quadrats and recorded environmental data. Probabilities of occupancy and density were higher when water velocity was low, the substrate was noncompacted, and sediment was dominated by fines ( less than4 mm). At mean water depth (0.34 m) and velocity (0.09 m/s), estimated densities in occupied quadrats were 4.8 lampreys/m2 (95%: 3.4–6.9) when the substrate was compacted, and fines were not dominant, and 21.1 lampreys/m2 (95%: 17.7–25.3) when the substrate was noncompacted and fines were dominant. Probabilities of detecting occupancy in a 1-m2 quadrat sampled by backpack electrofishing were 0.76 (95%: 0.64–0.87) when captured after visual observation and 0.80 (95%: 0.71–0.88) with blind sweeps (i.e., constantly moving the net regardless of observation). The probability of capturing a single lamprey in a quadrat sampled by blind sweeps was 0.32 (95%: 0.27–0.37). Sampling in paired 1-m2 quadrats facilitated concurrent examination of patterns in occupancy and density while accounting for capture probability, which could aid temporal monitoring of restored habitats. To the best of our knowledge, this is the first study to document occupancy and estimate densities of larval lampreys in habitats that underwent valley floor restoration to Stage 0. We observed both lamprey genera within 5 years of restoration. Aquatic restoration that increases low-velocity, noncompacted, fine sediment habitats could benefit lampreys.

Recent research into large wood for Stage Zero projects

November 2023

See the abstract from Daniel Scott's new article below or click the link to the article itself:

Valley bottom process reset, or the excavation of high surfaces and fill of incised channels combined with large wood addition, is a new method for creating multi-channel river-wetland corridors (also referred to as Stage 0 valley bottoms). Valley bottom process reset seeks to increase lateral flow and sediment connectivity, retain water and sediment, and kickstart geomorphic processes that may sustain aquatic and riparian habitat. This study uses this anthropogenic intervention to examine relationships among wood-induced hydraulic roughness, valley bottom topography, and geomorphic processes such as overbank flow and sediment transport, avulsion, sediment retention, and pool scour. Here, I present a 6-year case study of a two-phase valley bottom process reset along Deer Creek, Oregon. Kickstarting the floodplain reshaping processes required a substantial increase in roughness and hydrologic connectivity. The first phase of construction enhanced hydrologic but not sediment connectivity, failing to kickstart avulsion and floodplain reworking even during a likely 2- to 5-year recurrence interval flood. A second, more intensive phase of construction substantially reduced the threshold discharge necessary for overbank flow and floodplain reworking, as evidenced by the occurrence of these processes after only a less than 2-year recurrence interval flood. During this flood, a spatially distributed wood lattice rearranged into discrete jams that scoured pools, retained sediment, and drove geomorphically effective overbank flows. While valley bottom regrading likely contributed to these geomorphic effects, the spatial correlation between newly incised floodplain channels and areas of wood aggregation indicates wood's important role in driving floodplain reworking. I derive from these findings a conceptual model that details how wood drove floodplain reworking via two mechanisms: In-channel wood jams backwatered and constricted flow into the floodplain, and small wood jams formed in the floodplain forest further constricted flow through nascent channels to facilitate channel incision.