Abstract
Confluences are important sites for mixing within river networks. Past work has shown that mixing within confluences is highly variable; in some cases flows mix rapidly and in other cases flows remain unmixed far downstream of the confluence. The fluvial processes that govern mixing within confluences remain poorly understood. This study relates patterns and amounts of mixing to three-dimensional flow structure at three small confluences. It focuses on lateral fluxes of streamwise momentum, which theoretical considerations suggest should influence lateral mixing. Patterns and amounts of mixing differ at the three sites. Considerable mixing occurs at an asymmetrical confluence with strong helical motion within flow from the lateral tributary, which produces substantial differences in advective lateral transport of streamwise momentum over depth. Minor mixing occurs at a comparatively symmetrical confluence where incoming flows have relatively equal momentum fluxes; however, helical motion within one of the flows locally increases mixing. At a symmetrical confluence where one incoming flow has much greater momentum flux than the other, mixing occurs largely through progressive lateral shifting of the mixing interface toward the minor tributary because of the strong lateral flux of streamwise momentum by the dominant tributary. At all three confluences, lateral turbulent transport of streamwise momentum is an order of magnitude less than advective lateral transport of streamwise momentum. The study indicates that generalization of mixing at confluences remains challenging but that advective lateral fluxes of streamwise momentum related to secondary currents (helical motion) or primary flow (cross currents) greatly enhance mixing at confluences.
Original language | English (US) |
---|---|
Article number | e2019WR026817 |
Journal | Water Resources Research |
Volume | 56 |
Issue number | 9 |
DOIs | |
State | Published - Sep 1 2020 |
Keywords
- confluence
- mixing
- momentum
- hydrodynamics
ASJC Scopus subject areas
- Water Science and Technology
Fingerprint
Dive into the research topics of 'Advective Lateral Transport of Streamwise Momentum Governs Mixing at Small River Confluences'. Together they form a unique fingerprint.Datasets
-
Mixing Data for Three Small Confluences in East Central Illinois
Rhoads, B. L. (Creator), Lewis, Q. (Creator), Sukhodolov, A. (Creator) & Constantinescu, G. (Creator), University of Illinois Urbana-Champaign, Aug 1 2020
DOI: 10.13012/B2IDB-1255710_V1
Dataset