Channel incision, evolution and potential recovery in the Walla Walla and Tucannon River basins, northwestern USA

Abstract

We evaluated controls on locations of channel incision, variation in channel evolution pathways and the time required to reconnect incised channels to their historical floodplains in the Walla Walla and Tucannon River basins, northwestern USA. Controls on incision locations are hierarchically nested. A first-order geological control defines locations of channels prone to incision, and a second-order control determines which of these channels are incised. Channels prone to incision are reaches with silt-dominated valley fills, which have sediment source areas dominated by loess deposits and channel slopes less than 0·1(area) − − − − − 0·45 . Among channels prone to incision, channels below a second slope-area threshold (slope = = = = = 0·15(area) − − − − − 0·8) did not incise. Once incised, channels follow two different evolution models. Small, deeply incised channels follow Model I, which is characterized by the absence of a significant widening phase following incision. Widening is limited by accumulation of bank failure deposits at the base of banks, which reduces lateral channel migration. Larger channels follow Model II, in which widening is followed by development of an inset floodplain and aggradation. In contrast to patterns observed elsewhere, we found the widest incised channels upstream of narrower reaches, which reflects a downstream decrease in bed load supply. Based on literature values of floodplain aggradation rates, we estimate recovery times for incised channels (the time required to reconnect to the historical floodplain) between 60 and 275 years. Restoration actions such as allowing modest beaver recolonization can decrease recovery time by 17-33 per cent.

Ecosystem experiment reveals benefits of natural and simulated beaver dams to a threatened population of steelhead (Oncorhynchus mykiss)

“…This study provides further quantitative support to the proposal to reintroduce or expand beaver populations in their native range in North America and Eurasia to recover incised channels81435. However, the impacts of beaver reintroductions on fish populations, summarized in a recent review30, have been debated.…”

Channel adjustments and alteration of sediment fluxes in gravel‐bed rivers of North‐Eastern Italy: potentials and limitations for channel recovery

“…Our procedure is essentially qualitative and will need refinements (e.g. integrating the empirical approach with modelling), but it represents one of few examples where links between research (channel evolution and sediment dynamics) and application (restoration strategies) are investigated (Watson et al, 2002;Beechie et al, 2008;Brierley et al, 2008). Finally, it is worth noting that the procedure presented here aims to restore physical processes and to recover channel morphology, therefore it represents just a piece, albeit a fundamental one, of the broad-based interdisciplinary approach required for effective restoration (Federal Interagency Stream Restoration Working Group (FISRWG, 1998)).…”

Review of Tools for Identifying, Planning, and Implementing Habitat Restoration for Pacific Salmon and Steelhead

“…All three of these use a combination of empirical data and professional opinion to help identify prioritization goals, data needs, and criteria for scoring and prioritization; most use a combination of the approaches discussed by Beechie et al. (, ) and Roni et al. ().…”