GEOGRAPHY 12: RIVER FORMATIONS http://webs.cmich.edu/resgi/links.asp?mc=Other%20Resource%20Links&cad=Earth%20Science%20Animations&to=257&tod=River%20Animations

All part of the hydrologic cycle http://polaris.umuc.edu/cvu/envm/hydro/hydro.html `

DRAINAGE BASIN: an area of land from which a stream gets its water supply. It is a region that is grained by a single river What type is seen below?

RIVER CONFLUENCE: joining of 2 rivers

Dendritic A branching treelike drainage pattern Dendritic A branching treelike drainage pattern. In areas of uniform rock, with little distortion by folding or faulting, the rivers develop a random branching network similar to a tree

Dendritic

Trellis A rectangular drainage pattern Trellis A rectangular drainage pattern. It occurs when the rock structure steers streams into a parallel course, with tributaries joining at almost right angles..

Trellis drainage pattern

Radial A spokelike pattern of rivers Radial A spokelike pattern of rivers. These tend to flow away from the summit of a dome or volcano in all directions.

Radial pattern

Oahu, Hawaii

Mt. St. Helens, and what is left of radial drainage

River Stages

Following a river The Rhine River

Youthful River Youth stage-cuts a deep V-Shaped valley as the fast moving water transports material downstream. Dominated by erosion and very little depositionfeatures: include rapids, waterfalls, and various sizes of boulders along the river bed.

Mature Stage Mature Stage: Drainage pattern is evident. Vertical erosion is evident, but downstream lateral erosion of banks is evident as meanders and a flood plain take shape. Velocity slows and deposition is common. Deposition>erosion

Old Stage Old Stage: Extensive floodplain and meandering occur. River cuts across meanders to create oxbox lakes. Flooding of rich alluvium and natural levees are prominent. The river delta is well developed and continues to grow. Flooding deposits rich alluvium (sand, silt, and clay for farming) with natural levees along river banks

Rejuvenated River Rejuvenated Stage-The land has undergone a slow uplifiting and caused the river to return to a period of vertical erosion as was the case in the youthful stage Deep v-shaped valley prominent River cuts through the floodplain created until its elevation nears sea level

Work of rivers 3 functions Erosion Transportation Deposition http://www.bbc.co.uk/schools/gcsebitesize/geography/coastal/coastalprocessesrev4.shtml

Transportation http://library.thinkquest.org/28022/transport/index.html

River Meanders:

RIVER EROSION AND DEPOSITION: Cut off slope aka cutbank Point bar or slip off slope

River Erosion

River Bank erosion and deposition:

Point bar:

Lateral erosion

Stream Meandering Graded streams may erode horizontally in process called meandering Cutbanks form on outside of meanders (fast), while point bars form on the inside (slow) Stream Meandering

How Oxbow Lakes form:

Formation: When meander bends become giant loops, there is a thin piece of land left between the beginning and the end of the meander. This is the meander neck.

As the river neck becomes very narrow, the river can break through As the river neck becomes very narrow, the river can break through. For a short time, water flows both round the meander (which is now called a backwater) and across the meander neck.

Eventually the river cuts off the backwater completely and flows across what used to be the meander neck. For a short time, an oxbow lake is left behind.

The oxbow lake lasts until it becomes overgrown with weeds and filled in with soil. This happens quite quickly as it is cut off from the main river and therefore doesn't get any water. This is called a MEANDER SCAR

Oxbow Lake formation:

Oxbow lakes on a topographic map: http://www. sln. org

OPEN MEANDER: erode on outside, deposit on inside

MEANDER NECK: soon to be cut through by erosion

OXBOW LAKE: standing water once river cuts off meander

MEANDER SCAR: dried up oxbow lake.

Levees: formations common to old age rivers

Levees form by the spill-over of sediment during floods Levees form by the spill-over of sediment during floods. Next to the channel most of the coarse sediment is deposited and finer muds and clays are deposited farther away. Thus, over time these near-channel sand deposits will rise above the floodplain and form natural levees. Extends into a terrace over time-Let’s watch an animation!

levee

levee

levee

Braided stream:

Features of a typical floodplain

River Deltas A river carries sediment from its drainage basin toward the seaends up being deposited on the floodplain when the stream flow slows down. Some deposits are light enough to be deposited in the sea. They form river deltassand is deposited closest to shore (heaviest), followed by silt and clay (lighter) Below is an image of the Fraser River Deltaestuarine river delta

ARCUATE DELTA: Has many distributaries that carry water and sediment across a very symmetrical delta that has the shape of an inverted cove ex.NILE RIVER DELTA number of distributaries flowing across the delta (eg the Nile delta). An arcuate delta forms when a river meets the sea in a place where the waves, currents, and tides are strong

Nile River Delta

BIRD’S FOOT DELTA: From the picture, it is quite evident that it does not look like a bird's foot (C) delta as shown below. A bird's foot delta forms where sediment is deposited in relatively calm offshore waters. An example of a bird's foot delta is the Mississippi river delta.

ESTUARINE DELTA: e. g. , Seine River of France ESTUARINE DELTA: e.g., Seine River of France.  This type of delta has a river that empties into a long, narrow estuary that eventually becomes filled with sediment (inside the coastline). When the mouth of a river enters the sea and is inundated (overtaken) by the sea in a mix with freshwater and very little delta, it is called an estuary. Another example would be Delta, British Columbia http://www.semi.sd36.bc.ca/mleziva/unit6/U06L02.htm

A cuspate delta is formed when a river drops sediment onto a straight shoreline with strong waves. Waves force the sediment to spread outwards in both directions from the river's mouth making a pointed tooth shape with curved sides. An example is the Tiber delta in Italy.

Alluvial fans:Created by alluvial aggradation (ACCUMULATION) in areas of high relief where bedload-dominated streams flow out of mts onto plain – stream sweeps side to side over time, making fan shape – most common in desert climates

Dams and Reservoirs Dam – engineered obstruction across a river to control its flow – usu. holds back lake or reservoir Why dams? 1. Hydroelectric energy 2. Flood control 3. Enhance river navigation 4. Surface water supply Hoover Dam

Negatives of Dams Expense Refugees from areas flooded by dam Loss of ecosystems & scenery No floods/No soil replenishment in floodplain (downstream) Stop spawning fish from going upstream Increase in GHG’s because of lake where flora decomposes Disease: organisms that thrive in warm water eg. Schistosomiasis aka Bilharzia-quite evident in Egypt’s Aswan Dam http://en.wikipedia.org/wiki/Schistosomiasis Watch Animation http://www.brainpop.com/search/search.weml