The Lateral Migration of Groundwater-fed Streams
Abstract
Streams fed by groundwater grow in a way that preserves symmetry ofthe groundwater field in the vicinity of the spring, an idea adaptedfrom the problem of crack pattern formation in fracture mechanics(Cohen et al. 2015). As these streams branch, maintenance of thislocal symmetry manifests as a 2π /5 branchingangle. However, an averaging of thousands of streams from our fieldsite reveals that this angle is wider than 2π /5 within the first ∼ 5 meters of the junction. While self-similar growth at a2π /5 angle maintains symmetry near the spring, the height of thegroundwater field on either side of the channel grows increasinglyasymmetric downstream. We suggest that the resulting flux imbalancesto the valley sidewalls drive rearrangement of these rivers to balancethese fluxes, toward a symmetric configuration. We combine field dataand theoretical reasoning with model predictions to support andcharacterize this claim.
This mechanism need not be restricted to the vicinity of ajunction. We therefore seek its signature in the entire network, andintroduce a method for quantifying the typical radius of curvature ofnetwork channels | what we suggest to be the network-widemanifestation of this phenomenon | and we find that the radius curvature of rivers inour field site is on the order of 10 m, a length consistent withobserved deviations from the predicted 2π /5 bifurcationangle. Finally, we seek physical evidence that our proposed mechanismis responsible for this curvature. To this end, we measure the maximumslope along valley sidewalls as an estimate for the rate of lateralerosion, and find a correlation to flux asymmetry and curvature. Thissuggests flux asymmetry may drive stream migration, leading tosteepening of the incised valley wall. Our results suggests a singleprocess | migration in response to an asymmetric groundwater field |is responsible for both the wide bifurcation angle and network-widecurvature. Cohen, Y., Devauchelle, O., Seybold, H. F., Robert, S. Y., Szymczak,P., & Rothman, D. H. (2015). Path selection in the growth ofrivers. Proceedings of the National Academy of Sciences, 112(46),14132-14137.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2016
- Bibcode:
- 2016AGUFMNG13A1695Y
- Keywords:
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- 3315 Data assimilation;
- ATMOSPHERIC PROCESSES