Confluence

"[5] A natural phenomenon at confluences that is obvious even to casual observers is a difference in color between the two streams; see images in this article for several examples.

According to Lynch, "the color of each river is determined by many things: type and amount of vegetation in the watershed, geological properties, dissolved chemicals, sediments and biologic content – usually algae."

In hydraulic civil engineering, where two or more underground culverted / artificially buried watercourses intersect, great attention should be paid to the hydrodynamic aspects of the system to ensure the longevity and efficiency of the structure.

[9][10] The velocities and hydraulic efficiencies should be meticulously calculated and can be altered by integrating different combinations of geometries, components such a gradients, cascades and an adequate junction angle which is sympathetic to the direction of the watercourse’s flow to minimise turbulent flow, maximise evacuation velocity and to ultimately maximise hydraulic efficiency.

Rogers suggests that for the ancient peoples of the Iron Age in northwest Europe, watery locations were often sacred, especially sources and confluences.

[12] Pre-Christian Slavic peoples chose confluences as the sites for fortified triangular temples, where they practiced human sacrifice and other sacred rites.

Confluence of the Bhagirathi and Alaknanda Rivers to produce the Ganges at Devprayag , India
The same confluence viewed from upstream at a different time; note the swirl of sediment from the Alaknanda.
Confluence of the Mississippi, Missouri and Illinois rivers with normal water levels in 1991, and during flood in 1993
Hydrodynamic features of a river/flume confluence can be separated into six identifiable distinct zones, also called confluence flow zones.
Arroyo J. Benítez transition structure within the eastern abutment of the river Monterroso culvert network.
The fountain at Point State Park in Pittsburgh , at the apex of the confluence of the Allegheny (top) and the Monongahela
The White Nile and Blue Nile merge at Khartoum ; April 2013 satellite view
The Nam Khan flows into the Mekong at Luang Prabang in Laos
The confluence of the Jialing and the Yangtze in Chongqing . The Yangtze flows left to right across the bottom of the image.
The Kolam Biru in Kuala Lumpur
The Seine becomes a single channel at the west end of the Île de la Cité in Paris . The Pont Neuf can be seen.
The Mosel flows into the Rhine at Koblenz .
The triple confluence in Passau ; from left to right, the Inn , the Danube , and the Ilz .
Confluence of Oka and Volga rivers
The confluence of the Allegheny and Monongahela at Pittsburgh , forming the Ohio
The Ohio flows into the Mississippi at Cairo .
The Rideau Falls in Ottawa , where the Rideau River tumbles into Ottawa River at its mouth.
The confluence of the Rio Negro (black) and the Rio Solimões (turbid) near Manaus, Brazil .
A section of the Industrial Canal in New Orleans also serves as the channel for the Gulf Intracoastal Waterway and the Mississippi River-Gulf Outlet Canal. The waterways are said to be 'confluent'