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River Flows In You

July 2009
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Monday, July 13, 2009 at 12:55 AM
Geography Project: The Process

This is a video showing the process of constructing the model for the natural river landforms. We have decided on three river landforms : waterfall, meander and oxbow lake.


We will first show how we obtained the materials and put them to use.





The base for our model is constructed.





We have started placing plasticine on the base of the model.




The model is almost done.




In the model, we have clearly shown that the waterfall was formed as a result of the movement of the Earth's crust. The waterfall was actually a river, and when the Earth's crust slides along a fault line, part of the river bed is displaced resulting in a waterfall. As seen in the model, the sides are painted different colours to distinguish the different rock layers of different resistance.

In our model, the waterfall immediately flows into a meander. We cannot afford to have a long middle course due to space constraint, hence the middle course is very short.


Meanders are usually found in the middle or lower course, or where the floor of the valley is broad and the gradient is gentle. Erosion occurs on the outer bank of the meander, and the eroded sediments are transported to the inner bank where they are deposited.


Oxbow Lake

  • lateral erosion & undercutting occur on concave banks where the stream flows the fastest. Deposition on convex bank due to water of slow speed.

  • continuous erosion on concave bank & deposition on convex bank cause the formation of very pronounced meander with two neighbouring concave banks getting closer


  • two concave banks move closer to each other, forming a loop

  • loop becomes more distinct, and is then separated by the narrow neck of land

  • neck gets narrower with continual erosion & deposition

  • two banks eventually meet

  • sediments deposited dam up water in the cut-off, forming an oxbow lake

  • river flows in a straight path for a shorter distance, before meandering again

  • cut off from main river, oxbow lakes will eventually dry up due to evaporation, encouraging vegetation growth

NOTE! : Oxbow lake may not be permanent as water may dry up and be filled with sediment & vegetation growth.

at 12:54 AM
Pictures of the River Model
at 12:49 AM
Sharing: Oxbow Lake


Mount Moran reflected at Oxbow Bend.
at 12:28 AM
In Depth study: Meander

Meanders

Meanders are formed by a combination of the processes of erosion, transportation and deposition along a river. Meanders are curves or bends along a river which are usually found in the middle or lower course of a river, or where the floor of a valley is broad and the gradient is gentle.

At a meander, erosion occurs on the outer bank of a river, and the eroded sediments are transported to the inner bank where they are deposited. Here, the water in the channel moves in a spiral fashion. The speed of the river also differs along its outer and inner banks.



Along the outer bank, the speed of the river is high because there is less friction at the outer bank. Thus, the river has more energy and erosion can occur. Over time, the outer bank of the river gets undercut and a steep-sided bank, known as a river cliff, is formed.



The sediments removed from the outer bank are carried by the flow of the water and deposited along the inner bank. Deposition occurs at the inner bank because the friction between the inner bank and the water is greater than at the outer bank. This reduces the speed and causes the river to drop its load. Over time, as more sediments are deposited, the water becomes shallower at the inner bank and the river channel becomes asymmetrical. A gentle slope formed by the deposition of sediments along the inner bank, known as a slip-off slope, is formed. This process is repeated as the river moves downstream.

Example:


Examine closely and you can see how this meandering river has changed its course over the years. It's the River South Esk in Angus, Scotland.

Source: Earth: Our Home 3 (Full Geography
Sunday, July 12, 2009 at 12:48 AM
In Depth study: Waterfalls

Waterfalls

Waterfalls are sudden, steep, vertical flows of fast-flowing water falling from great heights. A waterfall is usually found in the upper course of a river where the gradient is steep.

Waterfalls are normally formed in two ways. They may be formed through the erosion of rocks of different resistance or through faulting.



Waterfalls form where the river bed has a layer of harder rock
and layer of softer rocks.



  1. The river erodes the less resistant rock more rapidly and this causes a change in the gradient of the river course, undercutting the harder rock.
  2. The hard, overhanging rock eventually collapses.
  3. Over time, the river plunges from a great height to hit the river bed below with tremendous force.
  4. A waterfall is formed.repeated pounding of the river bed may leave a depression at the base of the waterfall.
  5. The collapsed rocks fall into the plunge pool causing more erosion of the soft rocks and a deeper plunge pool.


A waterfall may also be formed through faulting. Faulting involves the movement of rocks along large cracks in the Earth's crust. This movement may result in the lifting of one block of land above the other. When a river flows down from the edge of the uplifted block, a water and plunge pool are formed.
  1. A river flows over land before displacement.
  2. A water is formed after the displacement of rocks along a fault. Repeated pounding of river bed causes a plunge pool to form.

Source: Earth: Our Home 3 (Full Geography)





Kuang Si is a beautiful series of tiered waterfalls and natural pools in dense tropical forest


Indiana Jones filmed Kuang Si Waterfall
at 12:15 AM
Terms

Erosion

As a river flows, pieces of rock are removed from the river bed and banks, and moved along the channel. This removal and movement of rocks downwards by the river is known as erosion. Erosion causes the river channel to deepen and widen.

Vertical erosion occurs when rocks and other materials on the river bed are removed, causing the channel to become deeper. Lateral erosion occurs when rocks and other materials along the sides of the channel are worn away. This causes the river channel to become wider.

























Type of erosionHydraulic actionCorrasion/ AbrasionAttritionSolution
Erosive Agent
Fast-flowing waterRock FragmentsRock FragmentsCarbonic acid in water
Impact
Rocks and materials along the river bed and river banks are loosened and eventually dislodged.Grinding action of the materials carried by the river results in the erosion of the river bed and banks.Previously eroded materials carried by the river collide against each other and are worn down into smaller pieces.Minerals in rock are dissolved and carried away in the solution.

Source: Earth: Our Home 3 (Full Geography)