The rate and extent of wind-gap migration regulated by tributary confluences and avulsions

Abstract

Abstract. The location of drainage divides sets the distribution of discharge, erosion, and sediment flux between neighboring basins and may shift through time in response to changing tectonic and climatic conditions. Major divides commonly coincide with ridgelines, where the drainage area is small and increases gradually downstream. In such settings, divide migration is attributed to slope imbalance across the divide that induces erosion rate gradients. However, in some tectonically affected regions, low-relief divides, which are also called wind gaps, abound in elongated valleys whose drainage area distribution is set by the topology of large, potentially avulsing side tributaries. In this geometry, distinct dynamics and rates of along-valley wind-gap migration are expected, but this process remains largely unexplored. Inspired by field observations, we investigate along-valley wind-gap migration by simulating the evolution of synthetic and natural landscapes, and we show that confluences with large side tributaries influence migration rate and extent. Such confluences facilitate stable wind-gap locations that deviate from intuitive expectations based on symmetry considerations. Avulsions of side tributaries can perturb stable wind-gap positions, and avulsion frequency governs the velocity of wind-gap migration. Overall, our results suggest that tributaries and their avulsions may play a critical role in setting the rate and extent of wind-gap migration along valleys and thus the timescale of landscape adjustment to tectonic and climatic changes across some of the tectonically most affected regions of Earth, where wind gaps are common.

Drainage reorganization induces deviations in the scaling between valley width and drainage area

“…Wind-gap migration induces rapid channel width adjustment on the extending reversed side, while on the beheaded side, adjustment is delayed, sustaining the gradient in unit stream power. This feedback suggests that the differing response of channel and valley width in different reorganization categories could maintain ongoing divide migration and may add to the slope and area feedbacks that were previously invoked as drivers of divide migration (Plant et al, 2014;Shelef and Goren, 2021;Willett et al, 2014). This width feedback could be easily overlooked if the channel width is parameterized based on a standard scaling relation, which is commonly assumed in large-scale landscape evolution models (e.g., Goren et al, 2014;Lague et al, 2014;Shobe et al, 2017;Yanites et al, 2013).…”

“…S11 in the Supplement). The main active flow path of this fan flows east toward the reversed section; however, an older path that drains westward toward the beheaded section is not completely abandoned and is likely active when the main flow path is flooded (Shelef and Goren, 2021). This setting reflects a recent episode of flow diversion and redistribution of discharge from the beheaded to the reversed valley.…”

“…(1), addition or reduction of the drainage area is expected to re-sult in channel and valley widening or narrowing, respectively. However, while drainage reorganization is capable of inducing relatively rapid drainage area changes, i.e., following river capture or repeated stochastic events (Shelef and Goren, 2021), width adjustment of channels and valleys most likely requires longer timescales (Brocard and van der Beek, 2006;Wright et al, 2022). Studies that measured channel widths in drainages that experienced recent anthropogenic drainage area perturbations reported ongoing width variations that prevailed for several decades (e.g., Jones, 2018;Snyder and Kammer, 2008).…”

“…West and downstream from the wind gap, beheaded valleys become indistinguishable from the undisturbed valleys with the trapezoid-shaped cross-section. Valley beheading is associated with either the receding cliff and its coinciding divide or with localized divide migration within the valley as part of a reversal process on the opposing side of the wind gap (e.g., Bishop, 1995;Harel et al, 2019;Shelef and Goren, 2021). The beheaded valleys have a valley bed morphology similar to the undisturbed category; thus, the formative flow width of the beheaded valleys is the entire width of the valley bottom.…”

Applicability of the landscape evolution model in the absence of rills

“…There are numerous applications of LEMs to understand different features of the surface morphology of natural landscapes (Yang et al, 2015;Mudd, 2016;Whipple et al, 2016Sinclair, 2017;Bonetti et al, 2020;Hooshyar and Porporato, 2021;Hu et al, 2021;Kwang et al, 2021;Shelef and Goren, 2021;Litwin et al, 2022). For example, Perron et al (2008) derived an expression for the distance between firstorder valleys and validated the formula via measurements from five different natural landscapes (Perron et al, 2009).…”