Scale-dependent interactions between wood and channel dynamics: Modeling jam formation and sediment storage in gravel-bed streams

Abstract

.[1] A stochastic model is used to investigate how the geomorphic function of wood changes with watershed scale, assuming wood recruitment occurs due to the mortality of individual trees, not to mass recruitment events such as landslides or episodic bank erosion. The model replicates the downstream decline in total wood load observed in the field, but predicts that the functional wood load peaks in channels having bankfull widths about 33% of the characteristic riparian tree height. The model also predicts that the greatest potential impact of jams on channel pattern-both in terms of sediment stored behind individual jams and the potential for jams to trigger avulsions-will typically be associated with channel widths between 25% and 67% of the riparian tree height. The simulation results are used to refine the categories that describe wood in alluvial channels, and the equivalent terms that describe the size of streams with forested riparian areas: small channels (or channels with large wood) are associated with widths less than 25% of the tree height; large channels (or channels with small wood) are associated with widths greater than 67% of tree height; and medium channels (or channels with intermediate wood) have widths between 25% and 67% of the tree height. We surmise that large wood acts primarily to store bed material (in small channels); intermediate wood tends to form channel-spanning jams, which can induce channel avulsions and create anabranched channel patterns (in medium channels); and small wood may increase the morphologic diversity, but does not store significant quantities of bed material or form channel-spanning jams capable of inducing stream avulsions (in large channels).Citation: Eaton, B. C., and M. A. Hassan (2013), Scale-dependent interactions between wood and channel dynamics: Modeling jam formation and sediment storage in gravel-bed streams,

Simulating riparian disturbance: Reach scale impacts on aquatic habitat in gravel bed streams

“…The simulation results contribute to a greater understanding of the longitudinal trends in wood loading and habitat availability that result from changes in channel size, as well as the effects of disturbances which interrupt these broad underlying patterns. As shown by Eaton and Hassan [2013], the total wood load in the base scenario is negatively related to channel size, characterized here by bankfull discharge. This pattern, which is supported by empirical data [e.g., Lienkaemper and Swanson, 1987;Bilby et al, 1989;Gurnell et al, 2002;Wohl and Jaeger, 2009], results from two primary factors.…”

“…The effects of wood are also limited in small streams as an increasing proportion of pieces are suspended on the channel banks [ Eaton and Hassan , ]. Functional wood load—the proportion of the total wood load located within the bankfull channel—and morphological impact are therefore greatest in intermediate‐sized streams [ Wohl and Jaeger , ; Eaton and Hassan , ].…”

“…Wood‐related sediment storage decreases with channel size, and pools are increasingly dictated by fluvial processes rather than obstructions to flow such as boulders or wood, resulting in regular pool and riffle spacing [ Fetherston et al ., ; Thompson , ; Montgomery and Buffington , ; Gurnell and Sweet , ]. The effects of wood are also limited in small streams as an increasing proportion of pieces are suspended on the channel banks [ Eaton and Hassan , ]. Functional wood load—the proportion of the total wood load located within the bankfull channel—and morphological impact are therefore greatest in intermediate‐sized streams [ Wohl and Jaeger , ; Eaton and Hassan , ].…”

Recent advances quantifying the large wood dynamics in river basins: New methods and remaining challenges

“…More detailed models have been used at regional and catchment scales to identify the potential source areas of large wood, including different recruitment processes, and to compute potential recruitable volumes of wood and transport rates [Czarnomski et al, 2008;Marcus et al, 2011;Wohl, 2011;Eaton et al, 2012;Eaton and Hassan, 2013]. Recent approaches have employed geographic information systems [Mazzorana et al, 2009;Rigon et al, 2012;Lucía et al, 2014b] and have applied fuzzy-logic principles [Ruiz-Villanueva et al, 2014a] to quantify wood potential volume in a spatially distributed way.…”

Exploring large wood retention and deposition in contrasting river morphologies linking numerical modelling and field observations

“…The obtained patterns of LW deposition predicted by the model together with in situ observations will increase the understanding of LW dynamics in the Czarny Dunajec River in particular and in other mountain rivers wider than the height of riparian trees (Gurnell et al ., ; Eaton and Hassan, ; Wyżga et al ., ) in general. In addition, recognition of the factors controlling preferential sites of LW deposition is crucial for the evaluation of flood risks related to LW accumulations in mountain rivers (Kundzewicz et al ., ).…”