Rivers and Coasts - What happens when rivers meet the coast
When two or more bodies of water meet, like rivers, it's called a confluence. This occurs when two . The Gulf of Alaska, where two oceans meet, but do not mix!. How can the unique world of river estuaries get better treatment from humans? Education is a vital first step. Estuary” is the generic term for the area where a river meets the sea. Definitions of “estuary” vary somewhat, but typically an estuary is the part of a river that is.
Estuaries are the borderlands between salt- and freshwater environments, and they are incredibly diverse both biologically and physically. The diversity and the high energy of the ecosystem make estuaries remarkably resilient. With a better understanding of these systems, we can reverse their decline and restore the ecological richness of these valuable, albeit muddy, environments.
How does an estuary work? When river water meets sea water, the lighter fresh water rises up and over the denser salt water. Sea water noses into the estuary beneath the outflowing river water, pushing its way upstream along the bottom. Often, as in the Fraser River, this occurs at an abrupt salt front. Across such a front, the salt content salinity and density may change from oceanic to fresh in just a few tens of meters horizontally and as little as a meter vertically.
Accompanying these strong salinity and density gradients are large vertical changes in current direction and strength. Pliny the Elder, the noted Roman naturalist, senator, and commander of the Imperial Fleet in the 1st century A.
But when the velocity difference reaches a certain threshold, vigorous turbulence results, and the salt and fresh water are mixed. Tidal currents, which act independently of estuarine circulation, also add to the turbulence, mixing the salt and fresh waters to produce brackish water in the estuary.
In the Fraser River, this circulation is confined to a very short and energetic frontal zone near the mouth, sometimes only several hundred meters long. In other estuaries, such as San Francisco Bay, the Chesapeake Bay, or the Hudson River, the salt front and accompanying estuarine circulation extend inland for many miles. The landward intrusion of salt is carefully monitored by engineers because of the potential consequences to water supplies if the salt intrusion extends too far.
For instance, the city of Poughkeepsie, N. Roughly once per decade, drought conditions cause the salt intrusion to approach the Poughkeepsie freshwater intake. The last time this happened, inextra water had to be spilled from dams upstream to keep the salt front from becoming a public health hazard. The lifeblood of estuaries Estuarine circulation serves a valuable, ecological function.
The continual bottom flow provides an effective ventilation system, drawing in new oceanic water and expelling brackish water.
This circulation system leads to incredible ecological productivity. Nutrients and dissolved oxygen are continually resupplied from the ocean, and wastes are expelled in the surface waters. This teeming population of plankton provides a base for diverse and valuable food webs, fueling the growth of some of our most prized fish, birds, and mammals—salmon, striped bass, great blue heron, bald eagles, seals, and otters, to name a few. The vigor of the circulation depends in part on the supply of river water to push the salt water back.
The San Francisco Bay area has become a center of controversy in recent years because there are many interests competing for the fresh water flowing into the Bay—principally agriculture and urban water supplies extending to Southern California. Estuarine circulation is also affected by the tides; stronger tides generally enhance the exchange and improve the ecological function of the system.
The Hudson estuary, for example, is tidal for miles inland to Troy, N. Some are self-inflicted; some are caused by the abuses of human habitation. An estuary, with all of its dynamic stirrings, has one attribute that promotes its own destruction: When suspended mud and solids from a river enter the estuary, they encounter the salt front. Unlike fresh water, which rides up and over the saline layer, the sediment falls out of the surface layer into the denser, saltier layer of water moving into the estuary.
As it drops, it gets trapped and accumulates on the bottom. Slowly, the estuary grows muddier and muddier, shallower and shallower.
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Occasionally a major flood will push the salt right out of the estuary, carrying the muddy sediment along with it. Sediment cores in the Hudson River indicate that sediment may accumulate for 10, 20, or even 50 years, laying down layers every year like tree rings.
Where the Rivers Meet the Sea
But then a hurricane or big snowmelt floods the river, wipes out the layers of sediment, and sends the mud out to sea. It is good because a big storm can keep an estuary from getting too shallow too fast. In fact, it appears that over the last 6, years, the natural dredging by large storms has maintained nearly constant water depth in the Hudson estuary.
It supports plenty of fish life and is distinguished be clear colored water, much cleaner than the Yangtze River of which it feeds into. The Yangtze River is the longest river in Asia and is very culturally and historically important to the country.
Unfortunately, its suffered industrial pollution in recent years, which is what gives it its brown color.Where The River Meets The Sea
The Rhine River, beginning its course in the Swiss Alps, flows throughout a good portion of Europe and has a history of being used for navigation and defense. It starts in Germany and eventually empties out into the Black Sea.
Where the rivers meet the sea | Penn State University
The Ilz River is a smaller mountain stream, running through the Bavarian forest before meeting with the 2 other rivers. It has a bluer color than the Danube and Inn Rivers, the later of which runs through Switzerland, Austria, and Germany. It has a much bluer color than the Rhone, the two of which meet in Geneva.
The Arve River also flows through France and Switzerland, but it receives its water from glaciers of the Chamoniz Valley, which gives it a high silt content and muddy-looking color. The meeting of two oceans in The Gulf of Alaska While technically not a confluence of two separate bodies of water, The Gulf of Alaska sometimes contains these stunning color variations.
The gulf contains different slow moving currents, or eddies, which harbor distinct sediments, one with a higher amount of heavier clay material that contains iron and changes the appearance of the water. Question of the Day: