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River Delta
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What is a River Delta?
A delta is a landform that isformed at the mouth of
a river where that river flowsinto an ocean, sea, estuary,
lake, reservoir, flat arid area,or another river.
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How are River Deltas Formed?
Deltas are formed from thedeposition of the sedimentcarried by the river as the flowleaves the mouth of the river.
Over long periods of time, this
deposition builds thecharacteristic geographicpattern of a river delta.
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Anatomy of aRiver Delta
Subaqueous delta -That part of the deltathat is below the low-
tide mark.Seaward, finer andfiner soil particles arefound.The seaward-mostportion has the finestsoils (clays) and is
called the prodelta.
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II. Subaerial delta - Thatpart above the low-tide mark.
A. Lower delta plain -That part governed byriverine/marineinteraction. Extends
landward to the limitof tidal influence. Allsalt and brackish floraand fauna are withinthis area.
B. Upper delta plain -That part governed byriverine depositionalprocesses.
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On the same figure, one can see thefollowing two additional categories:
1. Active delta - Thatpart that is stillactive and has water
channeling throughit carrying sediment.
2. Abandoned (orinactive) delta - That
part that was onceactive, but now hasreduced or no fluvial
activity.
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What are the nutrients in a RiverDelta?
Many nutrients are present in a River Delta,including many sedimentry mineral elements.The main ones are Nitrogen, Phosphorous andSulphur, which are all responsible for plant
growth. Others such as Carbon and hyddrogen are
present in chemical bonds to form
carbohydrates in plants and animals andproteins.
But mainly, geologically, Silicon in the form ofsand and sandstone. Calcium in limestone and
chalk.
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Arcuate delta Has many active, short distributaries
taking sediment to their mouths.
The receiving waters are rather
shallow and have relatively evenwave action arriving perpendicular tothe shore with minimal longshore
current. As the sediment exits the many
distributary mouths, the waves push it
back, so the coastline is rather smooth.
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Bird-foot delta Tend to have one or a very few
major distributaries near theirmouths.
The receiving basin has currents thatcarry the sediment away as it exits
the distributary mouth. There is a broad, shallow shelf that
deepens abruptly, so the trend is to
grow long and thin like a bird's toe.
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Cuspate delta Usually has one distributary
emptying into a flat coastline with
wave action hitting it head-on. This tends to push the sediment
back on both sides of the mouth,
with a "tooth" growing out ontothe shelf.
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Estuarine delta
This type of delta has a river thatempties into a long, narrowestuary that eventually becomesfilled with sediment.
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Ecological Threats to Deltas Human activities, including diversion of
water and the creationof dams for hydroelectric power or tocreate reservoirs can radically alter deltaecosystems.
Dams block sedimentation which can causethe delta to erode away.
The use of water upstream can greatly
increase salinity levels as less fresh waterflows to meet the salty ocean water.
While nearly all deltas have been impacted
to some degree by humans