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Abstract. The width of valleys and channels affects the hydrology, ecology,and geomorphic functionality of drainage networks. In many studies, thewidth of valleys and/or channels (W) is estimated as a power-law function ofthe drainage area (A), W=kcAd. However, in fluvial systemsthat experience drainage reorganization, abrupt changes in drainage areadistribution can result in valley or channel widths that are disproportionalto their drainage areas. Such disproportionality may be more distinguishedin valleys than in channels due to a longer adjustment timescale forvalleys. Therefore, the valley width–area scaling in reorganized drainagesis expected to deviate from that of drainages that did not experiencereorganization. To explore the effect of reorganization on valley width–drainage areascaling, we studied 12 valley sections in the Negev desert, Israel,categorized into undisturbed, beheaded, and reversed valleys. We found thatthe values of the drainage area exponents, d, are lower in the beheadedvalleys relative to undisturbed valleys but remain positive. Reversedvalleys, in contrast, are characterized by negative d exponents, indicatingvalley narrowing with increasing drainage area. In the reversed category, wealso explored the independent effect of channel slope (S) through theequation W=kbAbSc, which yieldednegative and overall similar values for b and c. A detailed study in one reversed valley section shows that the valleynarrows downstream, whereas the channel widens, suggesting that, ashypothesized, the channel width adjusts faster to post-reorganizationdrainage area distribution. The adjusted narrow channel dictates the widthof formative flows in the reversed valley, which contrasts with the meaningfullywider formative flows of the beheaded valley across the divide. Thisdifference results in a step change in the unit stream power between thereversed and beheaded channels, potentially leading to a “width feedback”that promotes ongoing divide migration and reorganization. Our findings demonstrate that valley width–area scaling is a potential toolfor identifying landscapes influenced by drainage reorganization. Accountingfor reorganization-specific scaling can improve estimations of erosion ratedistributions in reorganized landscapes.
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Revisiting Valley Flows
Abstract We introduce a quasi-analytical model of thermally induced flows in valleys with sloping floors, a feature absent from most theoretical valley wind studies. One of the main theories for valley winds—the valley volume effect—emerged from field studies in the European Alps in the 1930s and 1940s. According to that theory, along-valley variations in the heating rate arising from variations in valley geometry generated the pressure gradient that drove the valley wind. However, while those early studies were conducted in valleys with relatively flat (horizontal) floors, valleys with sloping floors are ubiquitous and presumably affected directly by slope buoyancy (Prandtl mechanism). Our model is developed for the Prandtl setting of steady flow of a stably stratified fluid over a heated planar slope, but with the slope replaced by a periodic system of sloping valleys. As the valley characteristics do not change along the valley, there is no valley volume effect. The 2D linearized Boussinesq governing equations are solved using Fourier methods. Examples are explored for symmetric (with respect to valley axis) valleys subject to symmetric and antisymmetric heating. The flows are 2D, but the trajectories are intrinsically 3D. For symmetric heating, trajectories are of two types: i) helical trajectories of parcels trapped within one of two counterrotating vortices straddling the valley axis and ii) trajectories of environmental parcels that approach the valley horizontally, move under and then over the helical trajectories, and then return to the environment. For antisymmetric heating, three types of trajectories are identified.
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- Award ID(s):
- 1921587
- PAR ID:
- 10563211
- Publisher / Repository:
- American Meteorological Society
- Date Published:
- Journal Name:
- Journal of the Atmospheric Sciences
- Volume:
- 82
- Issue:
- 1
- ISSN:
- 0022-4928
- Format(s):
- Medium: X Size: p. 45-69
- Size(s):
- p. 45-69
- Sponsoring Org:
- National Science Foundation
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