Biotic forcing militates against river meandering in the modern Bonneville Basin of Utah

Abstract

Biotic forcing on river meandering is a highly debated topic in sedimentology. Vegetation is assumed to hold a vital role on channel stability and sinuosity, for example through bank stabilization and pedogenic production of cohesive clays. However, statistically solid and causal relationships between vegetation density and river sinuosity remain largely untested in natural systems. This study investigates physical and biotic forcings on channel sinuosity in the Bonneville Basin of Utah (USA), an endorheic depression flanked by active fluvial networks ('washes') that display diverse vegetation density and channel-planform style. By means of remote sensing and ground-data collection, 58 washes are considered, 0Á1 to 90 km 2 in surface area and drained by trunk channels <45 m wide and <1Á2 m deep. Each wash is composed of a catchment basin connected downstream to an aggradational and distributive channel network. Statistically solid regressions highlight the primary roles played by base level and catchment size on fluvial morphogenesis. In contrast, no correlation is found between vegetation density and other parameters such as trunk-channel width or surface area of the largest meander in a wash. Similarly, no statistical correlation exists between vegetation density and meander size or sinuosity index. Rather, larger and more sinuous meanders are invariably associated with lower vegetation density. These results are corroborated by field evidence showing that sparse vegetation promotes flow disturbance, channel branching and bar braiding instead of stabilizing sediment surfaces. Thus, river meandering is attributed to cohesion offered by mud retention within the endorheic basin, as well as discharge and stream-power modulation along bifurcating and low-gradient channel reaches. Hence, this work demonstrates how meandering-channel patterns may arise from entirely physical forcings in the absence of vegetation.

Model for the Formation of Single‐Thread Rivers in Barren Landscapes and Implications for Pre‐Silurian and Martian Fluvial Deposits

“…Thus, there are only few modern examples of single‐thread rivers forming with muddy, unvegetated banks on Earth. As a test of the model, we compare predictions against shallow ( h = 1 m and h = 0.5 m) rivers that form in mud‐prone endorheic basins of the western United States and that are largely devoid of macroscopic plant life (Figures a and 4b; Quinn River, NV, Matsubara et al, ; Amargosa River, CA, Ielpi, ; washes of the Bonneville Basin, UT, Ielpi & Lapôtre, ; streams of the Toiyabe Basin, NV, Ielpi & Lapôtre, ).…”

“…Grain sizes in riverbanks of the Amargosa River, Bonneville Basin, and Toiyabe Basin were qualitatively constrained by Ielpi et al () and Ielpi and Lapôtre (, ) and consist of clay and silt with lenses of very fine to fine sand, similar to Lake Lahontan sediments forming the banks of the Quinn River, NV (Matsubara et al, ). The model correctly predicts that the Quinn River, NV, should be single threaded.…”

“…Predicted W / h for terrestrial rivers using input parameters representative of (a) shallow rivers forming within muddy unvegetated banks ( h = 1 m; Q = Quinn River, NV, Matsubara et al, ; A = Amargosa River, CA, Ielpi, 2018a), (b) yet shallower rivers forming within largely plant‐devoid banks (B = washes of the Bonneville Basin, UT, Figure a, Ielpi & Lapôtre, ; T = streams of the Toiyabe Basin, NV, Ielpi & Lapôtre, ), (c) deep rivers ( h = 10 m) without modeled vegetation‐added bank strength, and (d) deep rivers ( h = 10 m) with modeled vegetation‐added bank strength ( σ * = 29). Table summarizes model input parameters for each panel and Table data from natural rivers.…”

“…All data underlying the paper were published prior to our study (Moreton et al, 2003;Peakall et al, 2007;Bertoldi et al, 2009;Braudrick et al, 2009;van Dijk et al, 2012;DiBiase et al, 2013;Matsubara & Howard, 2014;Kite et al, 2015;Matsubara et al, 2015;Ielpi, 2018;Limaye et al, 2018;Ielpi & Lapôtre, 2019a, 2019b, are cited throughout where appropriate, and can be accessed directly through cited references.…”

“…Despite being rarely recognized (e.g., Gibling et al, ; Hartley et al, ; McMahon & Davies, ), at least some single‐thread rivers existed long before plants colonized land (Long, , ; Ielpi & Rainbird, ; Santos & Owen, ; Ielpi et al, , 2017). Moreover, some single‐thread rivers meander on Earth today in the virtual absence of macroscopic plant life (Matsubara et al, ; Ielpi, ; Ielpi & Lapôtre, ‐b; Santos et al, ). Finally, another barren endmember of single‐thread rivers comes from Mars.…”