Geology and Stream Dynamics

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What characterizes a superimposed stream?

It has the same stream pattern as the previous covering strata.

It flows over bedrock of similar lithology to the overlying strata.

It reflects the geology of the buried bedrock below.

It is let down from overlying strata onto different lithology bedrock. (correct)

Which statement about stream order classification is true?

The gradient of tributaries decreases downstream. (correct)

The length of tributaries decreases downstream.

The number of tributaries increases downstream.

The size of the valley is unrelated to the size of the stream.

What determines the drainage pattern of a consequent stream?

The type of rocks it flows over.

The age of the stream compared to the surrounding landscape.

The direction of the slope of the land. (correct)

The depth and width of the stream channel.

How does stream discharge change as one moves downstream?

It tends to increase. Signup and view all the answers

Which type of stream maintains its course across raised crust due to younger geological activity?

Antecedent stream Signup and view all the answers

What is the shape of the longitudinal profile of a typical stream?

Concave-upward Signup and view all the answers

Which factor does NOT influence the flow of water in natural streams?

Presence of vegetation Signup and view all the answers

Which type of stream is typically found on weak rock or geologic structures?

Subsequent stream Signup and view all the answers

What primary feature distinguishes braided streams from meandering streams?

The presence of interwoven channels Signup and view all the answers

Which type of stream is primarily associated with high-gradient areas and large sediment loads?

Braided streams Signup and view all the answers

In which area would you expect to find alluvial fans formed by sudden drops in stream velocity?

Mountain fronts Signup and view all the answers

What feature is typically found on the outside of meander bends where erosion occurs?

Cut banks Signup and view all the answers

What type of sediment transport dominates in braided streams?

Bed load Signup and view all the answers

How is sinuosity defined in the context of stream types?

The straight line distance downstream versus the channel length Signup and view all the answers

Which characteristic is typical for floodplains?

They border streams and are frequently inundated with flood waters. Signup and view all the answers

Which type of stream is noted for having a large suspended load and a subordinate coarse bed load?

Meandering streams Signup and view all the answers

What is the main difference between permanent and intermittent streams?

Permanent streams have continual groundwater seepage, whereas intermittent streams have a seasonally depleted groundwater supply. Signup and view all the answers

How does the shape of a stream channel influence its velocity of flow?

Semi-circular channels cause the least friction, leading to higher velocity. Signup and view all the answers

What does the term 'base level' refer to in the context of stream profiles?

The lowest point to which a stream can erode its channel. Signup and view all the answers

What primarily determines the competency of a stream regarding sediment transport?

The velocity of flow within the stream. Signup and view all the answers

What are the different modes of sediment transport in streams?

Dissolved load, suspended load, and bed load. Signup and view all the answers

What effect does the building of a dam have on local stream dynamics?

It forms a new local base level resulting in deposition upstream and erosion downstream. Signup and view all the answers

How does stream velocity relate to the stream gradient?

Stream velocity is directly proportional to the stream gradient. Signup and view all the answers

Which statement is true regarding the maximum flow in a channel?

The line of maximum flow is known as the thalweg. Signup and view all the answers

Study Notes

Superimposed Streams

Superimposed streams occur when water flows down from overlying strata onto buried bedrock with a different composition or structure.
The stream pattern is dictated by the geology of the previous overlying strata, not the current underlying rocks.

Stream Orders & Properties

As stream order increases, the following changes occur:
- Fewer tributaries downstream
- Longer tributaries downstream
- Reduced gradient downstream
- Wider and deeper channels downstream
- Valley size proportional to stream size

Stream Drainage Patterns

Consequent Streams: Determined by the slope of the land. Typically found on massive or gently sloping rocks, often with dendritic patterns.
Subsequent Streams: Flow through bands of weaker rock or geologic structures.
Antecedent Streams: Maintain their course across areas uplifted by younger folding or faulting.

Flow of Water in Streams

Influenced by:
- Stream gradient
- Stream discharge
- Stream velocity
- Channel shape
- Base level

Stream Gradient

Steep at the source, tapering to gentle slopes at the mouth.
Exhibit a concave-upward longitudinal profile.

Stream Discharge

Volume of water flowing past a point in a given time (measured in m³/sec).
Tends to increase downstream in tropical and temperate climates.
Turbulent flow occurs where velocity changes abruptly, especially near the channel bottom, keeping sediment in suspension.

Laminar vs. Turbulent Flow

Laminar Flow: Smooth, parallel streamlines, low velocity.
Turbulent Flow: Irregular, chaotic flow, high velocity.

Sediment Transport and Bedforms

The flow of water over sediment creates geometric features called bedforms, like ripples and dunes.

Alluvial Fans

Cone-shaped deposits of coarse-grained alluvial sediment.
Form along mountain fronts where high-gradient streams enter lowlands.
Sudden drop in velocity causes rapid sedimentation.
Dominated by gravel and sand.

Braided vs. Meandering Streams

Braided Streams:
- Interwoven converging and diverging channels.
- Separated by tear-shaped bars of sand and gravel.
- Dominated by bedload transport due to high flow velocities.
- Common in piedmont areas with steep gradients and heavy sediment loads, also found in glacial and desert regions.
Meandering Streams:
- Relatively high sinuosity (ratio of channel length to straight-line distance).
- Large suspended load, with subordinate coarse bedload.
- Thalweg (line of maximum depth) is close to the outer bank, causing erosion at cut banks.
- Curved sand bars or mud banks accumulate on the inner side of bends (point bars).
- Meander loops may become close enough for the river to cut across, forming abandoned meanders (oxbow lakes).

Floodplains

Wide, flat plains bordering streams, periodically inundated by flood waters.
Gravel and sand are mainly deposited within the channel (channel deposits).

Stream Velocity

Fastest flow where there is least friction, generally above the deepest part.
The line of maximum depth and strongest currents is the thalweg.
In bends, maximum velocity shifts to the outside of the bend, while minimum velocity occurs on the inside.
Stream velocity is proportional to stream gradient.
Stream's capacity to transport sediment increases greatly with velocity.

Channel Shape

Stream cross-sectional area increases with increasing discharge.
Channel shape influences flow velocity.
- A semi-circular channel offers the least surface area per unit volume, minimizing friction and maximizing velocity.
- Wide, shallow channels have higher friction, slowing flow.

Base Level

The lowest level to which a stream can erode its channel.
The sea is the ultimate base level.
Lakes, dams, and stream junctions act as local base levels.

Stream Load

Amount of material transported by a stream at a given time.
Generally less than its capacity.
Capacity: Maximum quantity of sediment a stream can carry past a point. Proportional to the discharge of the stream.
Competence: Maximum sediment size a stream can carry, determined by flow velocity.

Types of Sediment Load

Bed Load: Sediment rolling or sliding along the streambed.
Suspended Load: Sediment carried in suspension by the water.
Dissolved Load: Dissolved minerals transported by the water.

Sediment Transport

Mode of transport depends on the settling velocity of the particle.

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Description

This quiz covers the concepts of superimposed streams, stream orders, and the properties of different stream drainage patterns. Understand how geology influences the behavior of streams and the characteristics that change with stream order. Test your knowledge on geological formations and hydrology.