Post by Brindley on May 16, 2016 7:14:32 GMT 2
Some solid notes here on Fluvial Hydrology. Covers most of the AS information in good, basic detail.
www.brainshare.ug/open_content/notes/254-notes
eg:
www.brainshare.ug/open_content/notes/254-notes
eg:
3 Courses of a river
Upper
Place where the river begins
Many tributaries join up to form larger streams which in turn join to create river
Middle
River starts to meander
Many tributaries join the river
Lower
Meanders are common
Many distributaries
River flows toward the river mouth and enters the sea
Delta (land formed by sediments) may form at river mouth
Watershed: A stretch of land that surrounds drainage basin (a.k.a. boundary)
Drainage Basin: A river system that collects rainwater and comprises of streams and rivers
Tributaries: Streams that flow in the river which is mainly found in the upper course.
Distributaries: Branch out from the river which is mainly found in the river delta.
Confluence: Area where the stream meets the river
River Mouth: Place where the river meets the ocean
River Delta: Landform created at the mouth of the sea where the river flows into. It is formed by the deposition of the sediment carried by the river as it flows into the sea.
Upper
Place where the river begins
Many tributaries join up to form larger streams which in turn join to create river
Middle
River starts to meander
Many tributaries join the river
Lower
Meanders are common
Many distributaries
River flows toward the river mouth and enters the sea
Delta (land formed by sediments) may form at river mouth
Watershed: A stretch of land that surrounds drainage basin (a.k.a. boundary)
Drainage Basin: A river system that collects rainwater and comprises of streams and rivers
Tributaries: Streams that flow in the river which is mainly found in the upper course.
Distributaries: Branch out from the river which is mainly found in the river delta.
Confluence: Area where the stream meets the river
River Mouth: Place where the river meets the ocean
River Delta: Landform created at the mouth of the sea where the river flows into. It is formed by the deposition of the sediment carried by the river as it flows into the sea.
River Processes
The energy of a river determines the kind of processes that occur as the river moves along its course.
When the river has high energy, it is able to remove or erode rocks and other materials in its path.
The river may carry or transport these materials until it loses its energy and deposit them on the river bed.
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 ricks downstream by the river is known as erosion.
Vertical Erosion occurs when rocks and other materials n 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.
The 4 processes of Erosion
Hydraulic Action
The force of running water is the main cause of hydraulic action. In some rivers, the force or energy of fast-moving water is strong enough to loosen the rocks and soil along the river bed and banks.
Over time, the rocks and soil are dislodged and carried down the river. The river channel is eroded as a result.
Corrasion/Abrasion
Corrasion, also known as abrasion, occurs when rock fragments are dragged along the river bed or against the river banks.
This grinding action causes the river channel to widen and deepen as rocks and soil are scraped off the sides and bottom, and carried away with the water.
Corrasion is particularly effective during a flood when the river’s energy is at its maximum.
Attrition
The river carries a load of eroded materials which contain rock fragments and other materials.
These materials constantly collide with one another as they move. Over time, the collisions cause the materials to break down into smaller pieces.
Through this process, larger rocks are slowly broken down and their rough hedges are smoothed out.
This process of erosion, whereby the load carried by the river is eroded as the rocks collide with each other when they are carried along the river, is known as attrition.
Solution
As rain falls to the Earth’s surface, it reacts with the carbon dioxide present in the atmosphere, forming a weak acid known as carbonic acid. As this rainwater falls into rivers, the weak acid dissolves minerals present in the rocks on the river bed and banks.
For example, when a river flows over limestone, a chemical reaction occurs between the carbonic acid in the water and the calcium carbonate in the limestone.
This chemical reaction, which is called carbonation, dissolves the calcium carbonate to form calcium bicarbonate. Solution occurs because calcium bicarbonate is soluble in water.
Transportation
When a river has sufficient energy, materials will be carried or transported downstream.
These materials are carried downstream by 4 different transportation processes.
These processes depend on the energy of the river and the size of the material involved. For example, gravel can be transported by different transportation processes depending on the energy of the river.
Traction
Larger sized materials, such as boulders, pebbles and gravel, are found on the river bed.
If the river has sufficient energy, these large materials are moved downstream by the process of traction, where they roll or slide along the river bed.
Saltation
Saltation is the movement of materials downstream in a series of bouncing motions.
Smaller materials, such as coarse sand particles, may be moved along the river’s course in this manner as they get lifted up and dropped onto the river bed over and over again.
Suspension
Finer particles such as silt, clay and sand are carried along the river without touching the river bed.
These materials, which are held in suspension, usually form the greatest proportion of the river’s load. They are also responsible for giving the river a murky appearance.
Solution
As mentioned earlier, erosion rakes place when minerals found in rocks, such as calcium carbonate, dissolve in the river water. The running water will continue to transport these dissolved materials downstream. This process is known as solution.
Deposition
Happens when a river does not have enough energy to either erode or transport material. It then puts down or deposits the load it is carrying. This usually occurs when the speed of the river is reduced. E.g. During a period of low rainfall, the volume of water in the river drops, and so does the speed of the river. Thus the materials that are eroded in the river channel get deposited.
Deposition can occur along the lower, middle and upper courses of the river. Generally, larger particles such as rocks and boulders are deposited fist, followed by gravel, then sand and silt.
Factors that causes deposition
During a period of low precipitation
When a river enters a lake or sea, resulting in a decreases in its speed
When a river flows along the shallower side of a river channel, there is increased friction with the river bank that causes the river to slow down.
When the river receives a sudden increase in load or when incidents such as a landslide occur
When the river channel is obstructed by aquatic plants or protruding bed rocks.
The energy of a river determines the kind of processes that occur as the river moves along its course.
When the river has high energy, it is able to remove or erode rocks and other materials in its path.
The river may carry or transport these materials until it loses its energy and deposit them on the river bed.
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 ricks downstream by the river is known as erosion.
Vertical Erosion occurs when rocks and other materials n 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.
The 4 processes of Erosion
Hydraulic Action
The force of running water is the main cause of hydraulic action. In some rivers, the force or energy of fast-moving water is strong enough to loosen the rocks and soil along the river bed and banks.
Over time, the rocks and soil are dislodged and carried down the river. The river channel is eroded as a result.
Corrasion/Abrasion
Corrasion, also known as abrasion, occurs when rock fragments are dragged along the river bed or against the river banks.
This grinding action causes the river channel to widen and deepen as rocks and soil are scraped off the sides and bottom, and carried away with the water.
Corrasion is particularly effective during a flood when the river’s energy is at its maximum.
Attrition
The river carries a load of eroded materials which contain rock fragments and other materials.
These materials constantly collide with one another as they move. Over time, the collisions cause the materials to break down into smaller pieces.
Through this process, larger rocks are slowly broken down and their rough hedges are smoothed out.
This process of erosion, whereby the load carried by the river is eroded as the rocks collide with each other when they are carried along the river, is known as attrition.
Solution
As rain falls to the Earth’s surface, it reacts with the carbon dioxide present in the atmosphere, forming a weak acid known as carbonic acid. As this rainwater falls into rivers, the weak acid dissolves minerals present in the rocks on the river bed and banks.
For example, when a river flows over limestone, a chemical reaction occurs between the carbonic acid in the water and the calcium carbonate in the limestone.
This chemical reaction, which is called carbonation, dissolves the calcium carbonate to form calcium bicarbonate. Solution occurs because calcium bicarbonate is soluble in water.
Transportation
When a river has sufficient energy, materials will be carried or transported downstream.
These materials are carried downstream by 4 different transportation processes.
These processes depend on the energy of the river and the size of the material involved. For example, gravel can be transported by different transportation processes depending on the energy of the river.
Traction
Larger sized materials, such as boulders, pebbles and gravel, are found on the river bed.
If the river has sufficient energy, these large materials are moved downstream by the process of traction, where they roll or slide along the river bed.
Saltation
Saltation is the movement of materials downstream in a series of bouncing motions.
Smaller materials, such as coarse sand particles, may be moved along the river’s course in this manner as they get lifted up and dropped onto the river bed over and over again.
Suspension
Finer particles such as silt, clay and sand are carried along the river without touching the river bed.
These materials, which are held in suspension, usually form the greatest proportion of the river’s load. They are also responsible for giving the river a murky appearance.
Solution
As mentioned earlier, erosion rakes place when minerals found in rocks, such as calcium carbonate, dissolve in the river water. The running water will continue to transport these dissolved materials downstream. This process is known as solution.
Deposition
Happens when a river does not have enough energy to either erode or transport material. It then puts down or deposits the load it is carrying. This usually occurs when the speed of the river is reduced. E.g. During a period of low rainfall, the volume of water in the river drops, and so does the speed of the river. Thus the materials that are eroded in the river channel get deposited.
Deposition can occur along the lower, middle and upper courses of the river. Generally, larger particles such as rocks and boulders are deposited fist, followed by gravel, then sand and silt.
Factors that causes deposition
During a period of low precipitation
When a river enters a lake or sea, resulting in a decreases in its speed
When a river flows along the shallower side of a river channel, there is increased friction with the river bank that causes the river to slow down.
When the river receives a sudden increase in load or when incidents such as a landslide occur
When the river channel is obstructed by aquatic plants or protruding bed rocks.
