CHAP 13: Running Water *

Compare and contrast deltas, natural levees and alluvial fans.

1) Deltas form when a stream enters an ocean or lake and consist of three types of beds. 2) Natural levees - form parallel to the stream channel by successive floods over many years. 3) Alluvial fan - develop where a high-gradient stream leaves a narrow valley. Slope outward in a broad arc.

What are the factors that determine the velocity of a stream?

1) Gradient, or slope 2) Channel characteristics including shape, size, and roughness. 3) Discharge - the volume of water moving past a given point in a certain amount of time.

What are the two general types of a stream valley and some features associated with each?

1) Narrow valleys - V-shaped. Downcutting toward base level. Features often include rapids and waterfalls. 2) Wide valleys - Stream is near base level. Downward erosion is less dominant. Stream energy is directed from side to side forming a floodplain. Example of wide: Floodplains -Erosional floodplains -Depositional floodplains Meanders -Cut bank and point bar -Cutoffs and oxbow lakes

While working on a stream in your field study area, you find that the channel width is 20 meters, the channel depth is 2 meters, and the velocity is 1.2 meters/second. What is the discharge of this stream?

48 m3/s - Discharge is calculated by multiplying the channel width by the channel depth by the velocity.

In what way is a stream's base level related to its ability to erode?

Base level is the lowest point to which a stream can erode. Two general types of base level: - Ultimate (sea level) - Local or temporary Changing conditions causes readjustment of stream activities - Raising base level causes deposition - Lowering base level causes erosion

What are the common drainage patterns produced by streams and where do they form?

Dendritic - "branch pattern" develops on uniform bedrock Radial - "lines pulling away from each other" develops on isolated volcanic cones or domes. Rectangular - "rectangle shape branch" develops on highly highly jointed bedrock Trellis - develops in areas alternating weak and resistant bedrock.

How does deposition and erosion around meander loops occur?

Deposition occurs where water is moving the slowest along the inside of the loop. Erosion occurs where water is moving the fastest along the outside of the loop.

Stream terraces form as the result of which of the following processes?

Downcutting following the rise of the landscape produces stream terraces.

Why do floods occur and what are some basic flood-control strategies?

Floods are the most common and most destructive geologic hazard. Causes of flooding: - Result from naturally occurring and human induced factors Controlled by: Engineering efforts - Artificial levees - human-made walls of sand and mud built along sides of channel to increase height of riverbank (allows increase flow without flooding). - Flood-control dams - dam block flow of river and creates reservoir, which can be filled during heavy rainfall. - Channelization - involves changing channel characteristics (straightening, deepening, widening, clearing debris of channel or lining channel with concrete) allows more water to be funneled and flows faster. Nonstructural approach through sound floodplain management

What accurately describes the erosional processes of meanders that are incising and meanders that are in equilibrium?

Incising meanders erode primarily by downcutting. Meanders in equilibrium erode primarily in a side-to-side manner.

How does a stream's channel change over its length from headwaters to mouth?

The channel slope decreases toward a stream's mouth, the flow velocity increases; increases in channel size and discharge and decreases in channel roughness that occur downstream.

What is the source of energy that powers the water cycle?

The cycle of water leaving and returning to the Earth is known as the water cycle. The main source of energy that drives the water cycle is the SUN.

When considering the movement of water on Earth within the hydrologic cycle, what is responsible for driving this process?

The hydrologic cycle works because water exists on Earth in solid, liquid, and gaseous states.

What is likely to occur to an incised meander after it reaches equilibrium with its new base level?

The incised meander will cause only minor erosion of the canyon walls. - Incised meanders are generally cut into a hard rock that is not easily eroded. However, after enough time, water can erode any rock.

While working in the field, you come upon a stream that flows in a very deep V-shaped valley. Regarding the history of this stream, which of the following statements is most likely true?

The stream is relatively young. - The stream has a deep, V-shaped valley because it hasn't had time to erode laterally and develop a floodplain.

What are the different ways that sediment is transported downstream?

Transported material is called the stream's load. Types of load: 1) Dissolved load - "In solution" invisible tiny particles 2) Suspended load - "in suspension" slit, clay 3) Bed load - "by sliding, skipping or rolling along the bottom" sand, gravel, boulders Capacity - the maximum load a stream can transport.

TRUE OR FALSE: Deposition occurs at the mouth of a stream, the place with the lowest gradient.

True

Look at image and determine how flow will change as a result of stream piracy. The arrows indicate the original flow directions and the dotted line indicate where headward erosion has occurred.

Water would now flow from point A to point C.

The amount of meandering that occurs in a stream influences the gradient in which of the following ways?

With more meanders, the stream gradient decreases. - Meanders increase the length of the stream, causing the gradient to go down.

What would you expect to find on the outside bank of a stream meander loop?

a cut bank

What type of drainage pattern would you expect to find developing on rocks that have been folded and exposed by differential erosion over time?

a trellis drainage pattern

When the local gradient of a stream changes as it goes from a mountainous area to a large flat-lying area, what feature could form?

an alluvial fan

Water in the hydrologic cycle readily moves from the land to the oceans through several pathways. How does the vast majority of water get from the ocean to the land surface?

clouds and precipitation - Water evaporates from the ocean, clouds form, and precipitation brings water to the land surface.

Describe the erosion occurring during headward erosion.

erosion backwards at the start of the stream - The steep gradient at the head of the stream causes the start of the streams to be eroded in an upstream direction.

What are water gaps?

erosion through hills or ridges caused by a change in base level.

In a delta, sedimentary layers deposited under circumstances that appear to violate the Principle of Original Horizontality are found in which of the following circumstances?

foreset beds

In the hydrologic cycle, water that falls on land in the form of precipitation returns to the ocean by?

further precipitation runoff groundwater flow streams

What conditions are associated with high infiltration rates?

gentle slopes abundant vegetation permeable soil

Which of the following locations contains the most water in Earth's hydrosphere aside from the oceans?

glaciers - Glaciers rank second to oceans and contain 2.15 percent of Earth's water.

Which of the following choices does NOT directly affect stream velocity? (channel size, stream gradient, stream discharge, location of the drainage divide, channel shape)

location of the drainage divide

What are point bars in relation to meandering?

locations along a meandering stream where deposition occurs.

What are cut bars in relation to meandering?

locations along a meandering stream where erosion occurs.

Does the streambed slope get steeper, shallower, or stay the same downstream?

slope decreases downstream

What river is the largest river in North America?

the Mississippi River

What is stream discharge and how is it measured?

the volume of water moving past a given point in a certain amount of time. discharge is measured by multiplying a stream's cross-sectional area by its velocity

What causes meandering streams to downcut and become incised meanders?

uplift of the land the stream is flowing on

Classify the zones of the following: the headwaters, the main trunk of a stream, the mouth.

zone of erosion (the headwaters) zone of transportation (the main trunk of a stream) zone of deposition (the mouth).

What are the three main zones of a river system?

zone of erosion (the headwaters) zone of transportation (the main trunk of a stream) zone of deposition (the mouth).