Confluences occur where water and sediment from two or more rivers join one another. These features are important sites for mixing within river networks. Mixing is initiated at an interface where flows meet within a confluence. This mixing interface is often visible in aerial images when incoming flows have contrasting colors related to differences in materials (sediment/organic debris) transported by the rivers. The composite picture shows mixing interfaces at numerous confluences throughout the U.S. and illustrates how changes in contrast between the color of the combining rivers provides the basis for evaluating whether mixing occurs over short or long distances downstream of confluences. I will examine mixing at a large number of confluences based on color contrasts visible on aerial photographs. My research will shed light on spatial patterns of mixing rates by relating these rates to variations in potential controlling factors: how strong the flow of one river is compared to the other, angle between the two incoming flows, and orientation of the two incoming rivers in relation to the downstream river. Knowledge gained through this research is critical for understanding the role of confluences in dispersing contaminants that can affect water quality and biodiversity of river systems.
