Abstract
The width of valleys and channels affects the hydrology, ecology, and geomorphic functionality of drainage networks. Valley and channel widths are often estimated through a power-law scaling between width (W) and drainage area (A), and where lithologic variability or differential uplift rates dominate, width was suggested to scale with both slope (S) and drainage area, through the relation W = kb Ab Sc. However, in fluvial systems that experience drainage reorganization, abrupt changes in drainage area distribution can result in widths that are disproportional to their drainage areas. Consequently, in such cases, the width-area-slope scaling is expected to deviate relative to drainages that did not experience reorganization. To explore the effect of reorganization on width-area-slope scaling, we studied 12 valley sections in the Negev desert, Israel, categorized into undisturbed, beheaded, and reversed valleys. We found that the drainage area exponent, b, differs between valley categories, and that reversed valleys are characterized by a negative b exponent, indicating valley narrowing with increasing drainage area. A detailed study of a reversed valley reveals that unlike the negative b exponent that links drainage area to valley width, the relation between drainage area and channel width is best fitted with a positive b exponent. This difference indicates that the timescale of channel width adjustment to post-reorganization drainage area distribution is faster than that of the valley width adjustment. We find that the difference in channel width across the divide causes a step change in unit stream power between the adjusted reserved channel and the unadjusted, beheaded channel. Gradients in width and unit stream power across the divide, lead to a width-feedback that promotes ongoing divide migration and reorganization. The identified distinct width-area-slope scaling of reorganized valleys could assist in recognizing and constraining the dynamics of landscapes influenced by drainage reorganization and likely has critical implications for the distribution of erosion rates in reorganized landscapes.
Highlights
The width of channels and their hosting valleys control river’s dynamics and functionality with far-reaching 35 implications across a wide range of disciplines, from flood and seismic hazards (e.g., Lóczy et al, 2009; Mashael Al, 2010; Morell et al, 2020; Sampson et al, 2015), to river ecosystems and habitats (e.g., Beeson et al, 2018; Brussock et al, 1985; May et al, 2013; Sweeney et al, 2004), and to hydrological modeling (e.g., Looper et al, 2012)
Study area 2.1 Geologic and Geomorphic setting 135 We explore the scaling between the valley and channel width, drainage area, and slope along ephemeral valleys that incise into the southeastern Negev Highlands, Israel
We suggest that the comparison between the valley and channel width in reversed valley 12 (Fig. 6) demonstrates a temporal snapshot where the channel width 460 is adjusted to the new drainage area distribution inflicted by the drainage reversal, whereas the valley width is not yet adjusted to the same forcing (Fig. 6b), in accordance with the longer timescale expected for valley adjustment. 5.4 Implications to landscape evolution
Summary
The width of channels and their hosting valleys control river’s dynamics and functionality with far-reaching 35 implications across a wide range of disciplines, from flood and seismic hazards (e.g., Lóczy et al, 2009; Mashael Al, 2010; Morell et al, 2020; Sampson et al, 2015), to river ecosystems and habitats (e.g., Beeson et al, 2018; Brussock et al, 1985; May et al, 2013; Sweeney et al, 2004), and to hydrological modeling (e.g., Looper et al, 2012). A growing body of work focused on developing tools for automatic width extraction based on remotely-sensed data (e.g., Fisher et al, 2013; Gilbert et al, 2016; Hilley et al, 2020; Monegaglia et al, 2018; Roux et al, 2014; Rowland et al, 2016) These tools enabled a significant advancement in river research and management, they commonly focus on specific types of river morphology, and require parameter calibrations, as well as human supervision (Fryirs et al, 2019; Golly and Turowski, 2017). Due to these limitations, width of natural channels and valleys is more commonly estimated based on the widely recognized scaling relationships between valley and channel widths and fundamental basin properties such as discharge (or its proxy, drainage area), which could be relatively measured (e.g., Lavé and Avouac, 2001; Wobus et al, 2006). These scaling relationships are used frequently in landscape evolution models, where the width is parametrized based on the drainage area
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