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.
Highlights
Drainage divides play a pivotal role in controlling the geometry of fluvial landscapes and shaping their hydrologic and geomorphic functionality
Fixed confluence simulations with synthetic topography show that trunk–tributary confluences affect the velocity of wind-gap migration
Analysis of the wind-gap location through time (Fig. 5c) shows that the velocity of wind-gap migration decreases as it approaches a trunk–tributary confluence at the shrinking side and increases as the wind gap migrates across a confluence
Summary
Drainage divides play a pivotal role in controlling the geometry of fluvial landscapes and shaping their hydrologic and geomorphic functionality. Whereas drainage divides could be breached abruptly via river capture events (e.g., Bishop, 1995; Prince et al, 2010; Willett et al, 2014), a possibly more common process involves long-lasting and continuous divide migration at basin headwaters, where the divides are located along ridgelines (e.g., Willett et al, 2014; Goren et al, 2014b; Shelef and Hilley, 2014; Whipple et al, 2017; Beeson et al, 2017; Braun, 2017) In these high-relief settings, divide migration is linked to an imbalance in erosion rate across the hillslopes that bound the divide (Forte and Whipple, 2018). Given that channel erosion rate scales with channel gradient and drainage
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