Controls on spatial and temporal variations in sand delivery to salmonid spawning riffles

Abstract

Fine sediment infiltration into gravel interstices is known to be detrimental to incubating salmonid embryos. Infiltration into spawning riffles can show large spatial variations at the scale of a morphological unit and over time, with significant implications for embryo survival. Furthermore, some process‐based infiltration studies, and incubation‐to‐emergence models assume that fines are delivered to redds via suspension rather than bedload. This process‐based 12‐month study examined spatial patterns of predominantly sand infiltration into gravels in an upland trout stream, using infiltration baskets. An assessment of Rouse numbers for infiltrated sand indicated that it was transported predominantly as bedload at flow peaks. Clear temporal and spatial patterns existed, with highest rates of infiltration strongly associated with higher discharges (r2 = 0.7, p < .05). Seasonal variations in the delivery of different grain sizes were also a feature, with enhanced contributions of 0.5–2 mm sediment during elevated winter flows and 0.125–0.5 mm sediment during spring and summer; the latter is potentially harmful to the later stages of embryo incubation. Clear spatial patterns were also evident across riffles, with highest rates of infiltration tending to occur in areas of lower relative roughness—the areas competent to transport sand for longer periods. Incubation‐to‐emergence models should take into consideration spatial patterns of fine sediment dynamics at the pool–riffle scale, to improve prediction.

The sedimentology of gravel beds in groundwater‐dominated chalk streams: Implications for sediment modelling and management

“…The overall dataset meeting these criteria, subsequently, comprised 90 field sampling sites (Figure 1), encompassing 195 freeze‐core samples, across 11 chalk streams and their tributaries, from 10 studies (Acornley & Sear, 1999; Barron, 1992; Bateman, 2012; Beaumont et al, 1993; Carling, 1983; Greig, Sear, & Carling, 2005; Milan, 1994; Mitchell, 2015; Riley et al, 1999). These ranged from the River Piddle in Dorset, South England, to the River Babingley in Norfolk, East England (Figure 1).…”

“…Points are grouped by individual chalk streams as depicted in the figure legend. Values from non‐chalk stream gravel bed freeze cores are indicated by the grey region in (a) (Thoms, 1987; Lambert & Walling, 1988; Milan, 1994; Quin & Williams, 1999; Quin & Williams, 2000; Greig, Sear, & Carling, 2005; Twine, 2013). [Color figure can be viewed at wileyonlinelibrary.com]…”

“…Points are grouped by individual chalk streams as depicted in the figure legend. Values from non-chalk stream gravel bed freeze cores are indicated by the grey region in (a)(Thoms, 1987;Lambert & Walling, 1988;Milan, 1994;Quin & Williams, 1999;Quin & Williams, 2000;Twine, 2013). [Color figure can be viewed at wileyonlinelibrary.com]T A B L E 3 Bulk (framework and matrix) sediment characteristics for surface (0-10/15 cm) and subsurface (10/15-40 cm) layers in each of the chalk streams investigated.…”

Combining literature-based and data-driven fuzzy models to predict brown trout (Salmo trutta L.) spawning habitat degradation induced by climate change

“…The impact on salmonids caused by the excessive loading of river channels with fine sediments is common as a consequence of anthropogenic land use changes (Obruca and Hauer, 2017). However, this is not expected to occur in the Cabriel River Basin because the magnitude of peak flows, which are considered the predominant bedload transport agents (Milan, 2017), is not expected to rise significantly. Therefore, unlike other river segments where winter-flow increases will compromise the stability of the redds (Junker et al, 2015), neither sediment infiltration into gravel interstices nor redd scouring are likely to simultaneously impact brown trout reproduction.…”

Experiments on the Sediment Transport Along Pool‐Riffle Unit

“…At some point beyond the threshold flood (Jackson & Beschta, 1982), field‐based observations suggest that particle transport is generally associated with pool erosion, which consequently leads to riffle deposition (Lisle, 1979; Sear, 1996). Responses can also combine and exhibit a more complicated behavior, characterized by pool‐riffle bed load transport that is nonuniform, and unsteady (e.g., Chartrand et al., 2015; de Almeida & Rodríguez, 2011; Jackson & Beschta, 1982; Milan, 2013, 2017; Sear, 1996). The source of transport nonuniformity and unsteadiness can switch between the pool and riffle during a hydrograph event, with the transport dynamics dependent on a range of conditions that span from the magnitude and texture of the basin sediment supply, the shape and duration of the flood hydrograph, and the extent of upstream hydraulic influence by specific riffles (de Almeida & Rodríguez, 2011).…”