Channel mobility drives a diverse stratigraphic architecture in the dryland Mojave River (California, USA)

Abstract

The links between flood frequency and rates of channel migration are poorly defined in the ephemeral rivers typical of arid regions. Exploring these links in desert fluvial landscapes would augment our understanding of watershed biogeochemistry and river morphogenesis on early Earth (i.e. prior to the greening of landmasses). Accordingly, we analyse the Mojave River (California), one of the largest watercourses in the Great Basin of the western United States. We integrate discharge records with channel‐migration rates derived from dynamic time‐warping analysis and chronologically calibrated subsidence rates, thereby constraining the river's formative conditions. Our results reveal a slight downstream decrease in bankfull discharge on the Mojave River, rather than the downstream increase typically exhibited by perennial streams. Yet, the number of days per year during which the channel experiences bankfull or higher stages is roughly maintained along the river's length. Analysis of historical peak flood records suggests that the incidence of channel‐formative events responds to modulation in watershed runoff due to the precipitation in the river's headwaters over decades to centuries. Our integrated analysis finally suggests that, while maintaining hydraulic geometries that are fully comparable with many other rivers worldwide, ephemeral desert rivers akin to the Mojave are capable of generating a surprisingly wide range of depositional geometries in the stratigraphic record. © 2020 John Wiley & Sons, Ltd.

Planform‐asymmetry and backwater effects on river‐cutoff kinematics and clustering

“…With a pattern similar to other desert‐climate rivers in the Great Basin and beyond (e.g. Singer and Michaelides, 2014; Michaelides et al ., 2018; Ielpi et al ., 2020), our field estimates indicate that bankfull discharge, Q b (Table 1), is lowest upstream (Elko), reaches a maximum in the mid‐upper reaches (Beowave), and then decreases downstream, although irregularly, with a secondary high at Emigrant Canyon. Collectively, our estimates define a median ± 1σ Q b of m 3 s −1 .…”

“…To evaluate potential hydraulic controls on meander‐cutoff incidence (Lane, 1947; Schwenk and Foufoula‐Georgiou, 2016), we use a proxy for the backwater length scale, L b = h / S , as an indication of the distance over which non‐uniform flow conditions may occur upstream of an initial cutoff (Chow, 1959). To estimate the values of h needed to extrapolate the backwater length scale where we do not have ground measurements, we employ a best‐fit power law derived from Great Basin rivers: h = 0.05 w 1.07 ( R 2 = 0.76; from Ielpi et al ., 2020); local values of S along individual meander bends are approximated as S avg / χ ; whereas this approximation relies on comparatively coarse SRTM data, the large number of meanders in our dataset prevents biases from potentially spurious estimates. A nondimensional backwater length scale is then defined as , where L avg is the average of all meander lengths in our dataset (including both cutoff and non‐cutoff), and thus expresses the backwater length in units of meander lengths.…”

Linking the Remote Sensing of Geodiversity and Traits Relevant to Biodiversity—Part II: Geomorphology, Terrain and Surfaces

“…With the help of SRTM and in-situ information they were able to demonstrate that the loss of river meander was caused by a relative elevation of the land surface or a lowering of the sea level. Lelpi et al [232] used SRTM RS data to investigate the relationships between the incidence of floods and the speed of change to the channel migration rate in arid regions. They achieved this by combining the data from discharge records with channel migration rates, dynamic time-warping analysis, and chronologically calibrated subsidence rates derived from RS data.…”

Reconstruction of an extreme flood hydrograph and morphodynamics of a meander bend in a high‐peak discharge variability river (Powder River, USA)

“…Like other fluvial bars, stratal architecture and distribution of sedimentary facies in point bars are generally constructed when discharge reaches or exceeds bankfull conditions, whereas lower discharges reshape these deposits (Moody & Meade, 2014; Blom et al ., 2017; Naito & Parker, 2019; Francalanci et al ., 2020; Ielpi et al ., 2020). Although the importance of bankfull discharge in constructing bars is largely acknowledged, linking hydrology of river floods with related deposits has been the goal of a limited number of studies (Fielding et al ., 1999; Sambrook Smith et al ., 2010) and changes in sedimentary processes during floods is still poorly known.…”