Land formed by running waters
The Three stages of rivers
The three stages are youthful, mature and old stage.
For information on the three stages of rivers go to:
[PDF]
A valley formed by flowing water, or river valley, is usually V-shaped. The exact shape will depend on the characteristics of the stream flowing through it. Rivers with steep gradients, as in mountain ranges, produce steep walls and a narrow bottom. Shallower slopes may produce broader and gentler valleys, but in the lowest stretch of a river, where it approaches its base level, it begins to deposit sediment and the valley bottom becomes a floodplain.
Given above a river valley
Plunge Pools
A plunge pool can be a natural hydrologic fluvial landform feature or a constructed recreational garden feature. It is a stream pool, lake, or pond that is small in diameter, but deep.
Plunge pools are formed under the force of a natural source, such as a waterfall or rapids.
Plunge pools are erosional features which occur in the youthful stage of a river. When soft rock has been eroded back to a knickpoint, water constantly bombards its base. Because this rock is often less dense than surrounding strata, the water from the higher grade continues eroding downward.
A diagrammatic representation of plunge pools.
Incised and Entrenched meanders
If the slope of an established meandering stream is suddenly increased it will resume downward erosion – this happens when the base level of the stream is reduced, for example due to tectonic uplift of the region, a global fall in sea-level, collapse of a moraine-dammed lake downstream, or by capture of the stream by a steeper one. As the stream erodes downwards, its established meandering pattern will remain as a deep valley known as an incised meander or entrenched meander.
River Terraces
These are areas of flat land (located on either side of the flood plain) which are raised above the flood plain.
Paired and unpaired terraces: Terraces of the same elevation on opposite sides of either a stream or river are called paired terraces. They occur when it downcuts evenly on both sides and terraces on one side of the river correspond in height with those on the other side. Paired terraces are caused by river when the base level is lowered. Unpaired terraces occur when either a stream or river encounters material on one side that resists erosion, leaving a single terrace with no corresponding terrace on the resistant side.
Given Top- Paired terrace (observe carefully)
Middle- Unpaired Terrace
Bottom- Paired Terrace
Depositional Landforms
Alluvial Fans
An alluvial fan is a fan-shaped deposit formed where a fast flowing stream flattens, slows, and spreads typically at the exit of a canyon onto a flatter plain.
Owing to the flow as stream gradient decreases, coarse-grained solid material carried by the water is dropped. As this reduces the capacity of the channel, the channel will change direction over time, gradually building up a slightly mounded or shallow conical fan shape. The deposits are usually poorly-sorted.
Given above a desert alluvial fan( the river water is dried up)
Deltas
A delta is a landform that is formed at the mouth of a river where that river flows into an ocean, sea, estuary, lake, reservoir, flat arid area, or another river. Deltas are formed from the deposition of the sediment carried by the river as the flow leaves the mouth of the river. Over long periods of time, this deposition builds the characteristic geographic pattern of a river delta.
River deltas form when a river carrying sediment reaches a body of standing water,such as a lake, ocean, or reservoir. When the flow enters the standing water, it is no longer confined to its channel and expands in width. This flow expansion results in a decrease in the flow velocity, which diminishes the ability of the flow to transport sediment. As a result, sediment drops out of the flow and deposits. Over time, this single channel will build a deltaic lobe, pushing its mouth further into the standing water.
As the slope of the river channel decreases, it becomes unstable for two reasons. First, water under the force of gravity will tend to flow in the most direct course down slope. If the river breaches its natural levees, it will spill out onto a new course with a shorter route to the ocean, thereby obtaining a more stable steeper slope. Second, as its slope gets lower, the amount of sheer stress on the bed will decrease, which will result in deposition of sediment within the channel and a rise in the channel bed relative to the floodplain. This will make it easier for the river to breach its levees and cut a new channel that enters the body of standing water at a steeper slope. Often when the channel does this, some of its flow can remain in the abandoned channel. When these channel switching events occur a mature delta will gain a distributary network.
Given above delta of river Nile.
Flood Plains
A floodplain, or flood plain, is a flat or nearly flat land adjacent to a stream or river that stretches from the banks of its channel to the base of the enclosing valley walls and experiences flooding during periods of high discharge. It includes the floodway, which consists of the stream channel and adjacent areas that carry flood flows, and the flood fringe, which are areas covered by the flood, but which do not experience a strong current. In other words, a floodplain is an area near a river or a stream which floods easily.
Given picture of river and
floodplain
Natural Levees
The ability of a river to carry sediments varies very strongly with its speed. When a river floods over its banks, the water spreads out, slows down, and deposits its load of sediment. Over time, the river's banks are built up above the level of the rest of the floodplain. The resulting ridges are called natural levees.
Given the side of a natural levee of a river
Point Bars
A point bar is a depositional feature of streams. Point bars are found in abundance in mature or meandering streams. They are crescent-shaped and located on the inside of a stream bend, being very similar to, though often smaller than towheads, or river islands.
Point bars are composed of sediment that is well sorted and typically reflects the overall capacity of the stream. They also have a very gentleslope and an elevation very close to water level. Since they are low-lying, they are often overtaken by floods and can accumulate driftwood and other debris during times of high water levels.
Given point bars and cut-off bank
Meanders
A meander is formed when the moving water in a stream erodes the outer banks and widens its valley. A stream of any volume may assume a meandering course, alternately eroding sediments from the outside of a bend and depositing them on the inside. The result is a snaking pattern as the stream meanders back and forth across its down-valley axis. When a meander gets cut off from the main stream, an oxbow lake is formed.
Given a river in the shape of a meander.
Ox-bow lake
An oxbow lake is a U-shaped body of water formed when a wide meander from the main stem of a river is cut off to create a lake. This landform is called an oxbow lake for the distinctive curved shape.
Given a meander with an ox-bow lake.
Cut-off Bank
A meander cutoff occurs when a meander bend in a river is breached by a chute channel that connects the two closest parts of the bend. This causes the flow to abandon the meander and to continue straight downslope. Cutoffs are a natural part of the evolution of a meandering river, and have also been used to artificially shorten the length of meandering rivers for navigation.
Given the formation of a cut-off back
Slip-off bank
Most meanders occur in the region of a river channel with shallow gradients, a well-developed floodplain, and cohesive floodplain material.Deposition of sediment occurs on the inner edge, because the secondary flow of the river sweeps and rolls sand, rocks and other submerged objects across the bed of the river towards the inside radius of the river bend, creating a slip-off slope called a point bar.(refer to point bard given above)
Braided Channels
A braided river is one of a number of channel types and has a channel that consists of a network of small channels separated by small and often temporary islands called braid bars. Braided streams occur in rivers with high slope and/or large sediment load.
Braided rivers, as distinct from meandering rivers, occur when a threshold level of sediment load or slope is reached. In other words an increase in sediment load will over time increase the slope of the river. Therefore the river divides into to small-small rivers(distributaries) which separate out, rejoin and then separate out again.
Given a picture of a river with a braided pattern.
The Three stages of rivers
The three stages are youthful, mature and old stage.
For information on the three stages of rivers go to:
[PDF]
Classifying Rivers - The Three Stages of River Development
Erosional Landforms
River Valleys
Given above a river valley
Plunge Pools
A plunge pool can be a natural hydrologic fluvial landform feature or a constructed recreational garden feature. It is a stream pool, lake, or pond that is small in diameter, but deep.
Plunge pools are formed under the force of a natural source, such as a waterfall or rapids.
Plunge pools are erosional features which occur in the youthful stage of a river. When soft rock has been eroded back to a knickpoint, water constantly bombards its base. Because this rock is often less dense than surrounding strata, the water from the higher grade continues eroding downward.
A diagrammatic representation of plunge pools.Incised and Entrenched meanders
If the slope of an established meandering stream is suddenly increased it will resume downward erosion – this happens when the base level of the stream is reduced, for example due to tectonic uplift of the region, a global fall in sea-level, collapse of a moraine-dammed lake downstream, or by capture of the stream by a steeper one. As the stream erodes downwards, its established meandering pattern will remain as a deep valley known as an incised meander or entrenched meander.
River Terraces
These are areas of flat land (located on either side of the flood plain) which are raised above the flood plain.
Paired and unpaired terraces: Terraces of the same elevation on opposite sides of either a stream or river are called paired terraces. They occur when it downcuts evenly on both sides and terraces on one side of the river correspond in height with those on the other side. Paired terraces are caused by river when the base level is lowered. Unpaired terraces occur when either a stream or river encounters material on one side that resists erosion, leaving a single terrace with no corresponding terrace on the resistant side.
Given Top- Paired terrace (observe carefully)Middle- Unpaired Terrace
Bottom- Paired Terrace
Depositional Landforms
Alluvial Fans
An alluvial fan is a fan-shaped deposit formed where a fast flowing stream flattens, slows, and spreads typically at the exit of a canyon onto a flatter plain.
Owing to the flow as stream gradient decreases, coarse-grained solid material carried by the water is dropped. As this reduces the capacity of the channel, the channel will change direction over time, gradually building up a slightly mounded or shallow conical fan shape. The deposits are usually poorly-sorted.
Given above a desert alluvial fan( the river water is dried up)
Deltas
A delta is a landform that is formed at the mouth of a river where that river flows into an ocean, sea, estuary, lake, reservoir, flat arid area, or another river. Deltas are formed from the deposition of the sediment carried by the river as the flow leaves the mouth of the river. Over long periods of time, this deposition builds the characteristic geographic pattern of a river delta.
River deltas form when a river carrying sediment reaches a body of standing water,such as a lake, ocean, or reservoir. When the flow enters the standing water, it is no longer confined to its channel and expands in width. This flow expansion results in a decrease in the flow velocity, which diminishes the ability of the flow to transport sediment. As a result, sediment drops out of the flow and deposits. Over time, this single channel will build a deltaic lobe, pushing its mouth further into the standing water.
As the slope of the river channel decreases, it becomes unstable for two reasons. First, water under the force of gravity will tend to flow in the most direct course down slope. If the river breaches its natural levees, it will spill out onto a new course with a shorter route to the ocean, thereby obtaining a more stable steeper slope. Second, as its slope gets lower, the amount of sheer stress on the bed will decrease, which will result in deposition of sediment within the channel and a rise in the channel bed relative to the floodplain. This will make it easier for the river to breach its levees and cut a new channel that enters the body of standing water at a steeper slope. Often when the channel does this, some of its flow can remain in the abandoned channel. When these channel switching events occur a mature delta will gain a distributary network.
Given above delta of river Nile.
Flood Plains
A floodplain, or flood plain, is a flat or nearly flat land adjacent to a stream or river that stretches from the banks of its channel to the base of the enclosing valley walls and experiences flooding during periods of high discharge. It includes the floodway, which consists of the stream channel and adjacent areas that carry flood flows, and the flood fringe, which are areas covered by the flood, but which do not experience a strong current. In other words, a floodplain is an area near a river or a stream which floods easily.
Given picture of river and floodplain
Natural Levees
The ability of a river to carry sediments varies very strongly with its speed. When a river floods over its banks, the water spreads out, slows down, and deposits its load of sediment. Over time, the river's banks are built up above the level of the rest of the floodplain. The resulting ridges are called natural levees.
Given the side of a natural levee of a riverPoint Bars
A point bar is a depositional feature of streams. Point bars are found in abundance in mature or meandering streams. They are crescent-shaped and located on the inside of a stream bend, being very similar to, though often smaller than towheads, or river islands.
Point bars are composed of sediment that is well sorted and typically reflects the overall capacity of the stream. They also have a very gentleslope and an elevation very close to water level. Since they are low-lying, they are often overtaken by floods and can accumulate driftwood and other debris during times of high water levels.
Given point bars and cut-off bankMeanders
A meander is formed when the moving water in a stream erodes the outer banks and widens its valley. A stream of any volume may assume a meandering course, alternately eroding sediments from the outside of a bend and depositing them on the inside. The result is a snaking pattern as the stream meanders back and forth across its down-valley axis. When a meander gets cut off from the main stream, an oxbow lake is formed.
Given a river in the shape of a meander.Ox-bow lake
An oxbow lake is a U-shaped body of water formed when a wide meander from the main stem of a river is cut off to create a lake. This landform is called an oxbow lake for the distinctive curved shape.
Given a meander with an ox-bow lake.Cut-off Bank
A meander cutoff occurs when a meander bend in a river is breached by a chute channel that connects the two closest parts of the bend. This causes the flow to abandon the meander and to continue straight downslope. Cutoffs are a natural part of the evolution of a meandering river, and have also been used to artificially shorten the length of meandering rivers for navigation.
Given the formation of a cut-off backSlip-off bank
Most meanders occur in the region of a river channel with shallow gradients, a well-developed floodplain, and cohesive floodplain material.Deposition of sediment occurs on the inner edge, because the secondary flow of the river sweeps and rolls sand, rocks and other submerged objects across the bed of the river towards the inside radius of the river bend, creating a slip-off slope called a point bar.(refer to point bard given above)
Braided Channels
A braided river is one of a number of channel types and has a channel that consists of a network of small channels separated by small and often temporary islands called braid bars. Braided streams occur in rivers with high slope and/or large sediment load.
Braided rivers, as distinct from meandering rivers, occur when a threshold level of sediment load or slope is reached. In other words an increase in sediment load will over time increase the slope of the river. Therefore the river divides into to small-small rivers(distributaries) which separate out, rejoin and then separate out again.
Given a picture of a river with a braided pattern.
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