What type of geology exists in estuaries

In the animation below, rising waters flood a low-lying river valley, creating a coastal plain estuary. The Chesapeake Bay center and Delaware Bay upper right are both examples of drowned river valley estuaries. Credit: NASA. Bar-built or restricted-mouth, estuaries occur when sandbars or barrier islands are built up by ocean waves and currents along coastal areas fed by one or more rivers or streams.

The streams or rivers flowing into bar-built estuaries typically have a very low water volume during most of the year. Under these conditions, the bars may grow into barrier beaches or islands and the estuary can become permanently blocked. The area between the coast and the barrier beaches or islands are protected areas of calm water called lagoons.

Barrier beaches or islands break the impact of destructive ocean waves before they can reach the estuary and mainland, consequently protecting them. The barrier beaches take the brunt of the waves' force and are sometimes completely washed away, leaving the estuary and coast exposed and vulnerable.

During heavy rains, large volumes of water flowing down the river or stream can also completely wash away small bars and reopen the mouth of the estuary. The coast of North Carolina consists of a series of bar-built estuaries. These drastic changes typically occur along fault lines during earthquakes. If the depression sinks below sea level, ocean water may rush in and fill it.

To create more space for homes and businesses, Indonesian officials have dredge d the Ciliwung River and Java Bay. The sand and silt dredged from the river bottom and seafloor fortify the city's beaches and create new land. Land reclamation comes at a price, however. Jakarta's fisheries are disrupted by the dredging.

This reduces the potential profits for restaurants and markets, as well as fishers. Destroying the estuary also creates the conditions for flooding.

Estuaries provide a natural barrier to ocean waves, which can erode the shoreline and destroy coastal homes and businesses. Jakarta is particularly at risk for tsunami damage, as the area experiences frequent earthquakes. Pollution Pollution accumulate s in estuaries. The Hudson-Raritan Estuary, where the Hudson and Raritan rivers meet the Atlantic Ocean, is one of the most-trafficked and most-polluted estuaries in the world.

Debris in the estuary, including fuel, garbage, sewage, and ballast , remained unregulated for decades. Runoff from agriculture and industry in New York and New Jersey also contributed a toxic estuarine environment. Industrial waste and pesticide s travel downstream and settle in the water and sediment of the estuary. Today, strict regulations and community activities are working to protect and restore the Hudson-Raritan Estuary.

The restoration of oyster beds is an important part of many projects. Oysters are a keystone species in the estuary, filter feeder s that naturally help regulate toxins in the water. Millions of oyster beds greeted Henry Hudson when he entered the river in By the middle of the 20th century, however, the few remaining oysters were too toxic for human consumption. Today, several environmental groups are establishing oyster beds to repopulate the region's native species and reduce pollution in the estuary.

Overfishing Many estuaries have been overfish ed. Pacific bluefin tuna are not endangered, but their range has been drastically reduced. Japan provides one of the largest markets for bluefin tuna, and the fish used to swim in the estuary of Tokyo Bay.

Bluefin tuna are large, predatory fish. They require an expansive habitat and many kilograms of food every day. As Tokyo's population grew and technology made it easier to catch more fish with less time and money, Tokyo Bay's bluefin tuna population shrank. Today, there is not a bluefin tuna population in Tokyo Bay. However, Japanese scientists have established a successful tuna fish farming technique. Farm-raised tuna does not have a direct environmental impact on the Tokyo Bay estuary.

Indonesian, American, and Japanese governments and environmental groups struggle to promote sustainable development in estuaries. Sustainable development aims to preserve the environment while satisfying people's economic standard of living.

Edo Tokyo, the most populous city in the world, was originally known as Edo, which means "estuary. Largest Estuary in the World Because the definition of "estuary" is fluid, determining which one is the world's largest is an ongoing debate.

However, many scientists say that that St. Lawrence River, which connects the Great Lakes to the Atlantic Ocean, is the world's largest estuary. The St. Lawrence River is about 1, kilometers miles long. Between Land Some Native Americans called estuaries the "Between-Land" because they are not quite land and not quite water. Also called an alpha predator or top predator. Hurricanes are the same thing as typhoons, but usually located in the Atlantic Ocean region.

The last ice age peaked about 20, years ago. Also called glacial age. Usually rivers enter another body of water at their mouths. Pesticides can be fungicides which kill harmful fungi , insecticides which kill harmful insects , herbicides which kill harmful plants , or rodenticides which kill harmful rodents.

Also called an autotroph. Also called a storm tide. The audio, illustrations, photos, and videos are credited beneath the media asset, except for promotional images, which generally link to another page that contains the media credit. The Rights Holder for media is the person or group credited.

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If no button appears, you cannot download or save the media. Text on this page is printable and can be used according to our Terms of Service. Any interactives on this page can only be played while you are visiting our website. The system will simply continue to adjust its form in response to changes in energy inputs and constraints. These changes are generally internal to the estuary system and as a consequence it is the internal features that exhibit the range of responses outlined as the system searches for an optimum steady state.

Thus a progressive increase in river flows might cause channels to enlarge a transition , whereas a major flood event might cause channel switching a switch in position , or a switch from meandering to braided channels a switch in form. The first two are essentially changes in the given state. In contrast, the switch in form is an example of moving to a different state, for the channel feature, but not the estuary as a whole.

This provides a basis for thinking about the overall condition of the system and how specific features within it may behave. However the interaction of processes and form remains something of a conundrum. Although the size and shape of an estuarine channel is a response to tidal processes, it is nevertheless apparent that tidal discharge is itself dependent on the morphology of the estuarine channel since this determines the overall tidal prism.

Entering this loop requires some of the constraints in the system to be identified. One of the principal constraints that defines the size and shape of an estuary must be the antecedent form of the catchment basin, as already discussed. This determines the tidal length of the estuary, a characteristic dimension, which is dependent on the macro-scale slope of the coastal plain, fluvial discharge, and the tidal range in the nearshore zone.

The tidal range and morphology within the estuary is then a response to these independent factors. In some specific cases, further constraints to the closed cause-effect system are present. These constraints may be geological features such as sills, moraines or changes in geological strata, which limit control how the estuary can adjust. Equally, anthropogenic limits to width or depth, such as urban areas or harbour facilities, can constrain how an estuary responds to changing conditions.

In each case, the identification of such constraints can be seen as a method of reducing the number of degrees of freedom and providing a point of entry into the cause-effect feedback loop. Consequently, when examining development proposals or new activities, it is essential that the local and estuary wide implications be taken into account.

An estuary forms a mix of habitats depending on the prevailing constraints. If the constraints are changed, then the estuary will adjust to establish a new dynamic equilibrium, consistent with the existing and new constraints. This then runs the risk of establishing an even more artificial situation simply to meet societal preferences. A more preferable approach is, therefore, to take advantage of any opportunity that will increase the room in which the estuary can move, to respond to such things as sea level rise, by removing unnecessary constraints.

The Estuary Guide Google the Guide. Print PDF of this page. You have JavaScript turned off! Chapter 3 Estuary setting Chapter summary There are many types of estuary determined by their geological setting and dominance of particular processes. This chapter: Outlines estuary classification and setting according to topographical and geomorphological classification Figure 3.

Figure 3. Property Definition or reference Lengths Usually overall and to key change points e. Plan Areas Helps to include area of catchment and floodplain as well as estuary area at various elevations.

Features such as saltmarsh and intertidal may also be analysed individually. Cross-sectional areas Typically at the mouth and tidal limit. Volumes Usually in terms of volume below a given level e. Useful to also examine variation with chainage. Widths and Depths Indicative values at mouth, tidal limit and as an average over estuary length.

Tidal levels and range Spring and neap values at locations along the estuary. Freshwater flows Magnitude of annual mean daily flow rate and peak values.

Geology Usually mapped from available borehole records and provides essential information on potential constraints to long-term change. Geomorphology Mapped from maps, charts, aerial photographs, remote sensing images and field survey data to show all major forms - includes features such as saltmarsh, mudflat, cheniers, spits and nesses, bed forms, artificial channels and reclamations, ridges, cliffs, dunes, etc. Estuary number Indicates degree of stratification Ippen, Tidal wavelength l Simplistically this can be obtained using linear wave theory and either the depth at the mouth or the average depth.

Ippen gives a method of computing the wave number and hence the wavelength for a standing wave, including friction. Tidal asymmetry Examination of the duration and magnitude of flood and ebb velocities, together with timing of slack waters provides a useful indication of potential movement of coarse and fine sediments and the type of tidal basin Dronkers, ; Dronkers, Positive values indicate flood dominance.

Google the Guide. Diastrophic [1] embayment. Glacial origin, exposed rock platform set within steep-sided relief and with no significant mud or sand flats. River or marine in origin i. Helps to include area of catchment and floodplain as well as estuary area at various elevations. Usually in terms of volume below a given level e. Usually mapped from available borehole records and provides essential information on potential constraints to long-term change.