A confluence occurs when two or more flowing bodies of water join together to form a single channel. Confluences occur where a tributary joins a larger river, where two rivers join to create a third or, where two separated channels of a river, having formed an island, rejoin downstream.
This earth cache is placed at the confluence of the King and Queen rivers. The King river is to your left when looking at the confluence from the coordinates and the Queen river is to the right.
Confluences are studied in a variety of sciences. Hydrology studies the characteristic flow patterns of confluences and how they give rise to patterns of erosion, bars, and scour pools. The water flows and their consequences are often studied with mathematical models. Confluences are relevant to the distribution of living organisms (i.e., ecology) as well; "the general pattern [downstream of confluences] of increasing stream flow and decreasing slopes drives a corresponding shift in habitat characteristics."
Another science relevant to the study of confluences is chemistry, because sometimes the mixing of the waters of two streams triggers a chemical reaction, particularly in a polluted stream. The United States Geological Survey gives an example: "chemical changes occur when a stream contaminated with acid mine drainage combines with a stream with near-neutral pH water; these reactions happen very rapidly and influence the subsequent transport of metals downstream of the mixing zone."
A natural phenomenon at confluences that is obvious even to casual observers is a difference in colour between the two streams; see images in this article for several examples. According to Lynch, "the colour 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." Lynch also notes that colour differences can persist for miles downstream before they finally blend completely.
River confluence flow zones
Hydrodynamic features of a river/flume confluence can be separated into six identifiable distinct zones, also called confluence flow zones.
Hydrodynamic behaviour of flow in a confluence can be divided into six distinct features which are commonly called confluence flow zones (CFZ). These include
Stagnation zone
Flow deflection zone
Flow separation zone / recirculation zone
Maximum velocity zone
Flow recovery zone
Shear layers
To Log this cache please answer the following questions and send a message to the owner
1) Slightly downstream from the coordinates the confluence is stark, explain what you see there
2) The Queen River is a distinct colour, explain the colour and why it might be this colour
3) The King River is also a distinct colour, explain the colour and why it might be this colour
4) Take a photo of the confluence with your GPS, yourself or your thumb in the photo and upload with your log.
You can log this immediately, but please send answer within 2 weeks