Ch 16

Which one of the following does not apply to stream turbulence and average velocity?  A) channel shape; bed roughness B) laminar flow; dissolved load C) discharge; stream gradient  D) stream gradient; channel roughness

B) laminar flow; dissolved load

A stream begins at an elevation of 200 meters and flows a distance of 400 kilometers to the ocean? What is the average gradient? 2 m/km 2 km/m 0.5 m/km 1 km/m

0.5 m/km

Which one of the following statements is true concerning natural levees? A) Depositional features formed at times of low discharge. B) Mostly fine sand and silt that build up during floods.  C) Erosional features left behind when meander cutoff occurs. D) Form the high, steep banks of a downcutting stream.

B) Mostly fine sand and silt that build up only during floods. 

What is the base level of a stream and what does it represent? How does ultimate base level differ from local base level? Give some examples of local base levels.

Base level- the downward limit to stream erosion (represents the lowest elevation at which a stream can erode its channel) Ultimate base level is sea level while local base levels are lakes or resistant rock layers that temporarily prevent further erosion

How does a water gap form?

Both antecendent and superposed streams can create water gaps.

Which of the following is not part of the hydrologic cycle? Water evaporating from a lake Water infiltrating into the soil and bedrock Calcium carbonate dissolving in soil water and groundwater Water moving into creeks and streams following a rainstorm

Calcium carbonate dissolving in soil water and groundwater

Which of the following describes the total sediment load transported by a stream? Capacity - is the maximum load of solid particles a stream can transport per unit time. the greater the discharge the greater the stream's capacity for hauling sediment Discharge - measure most often used to compare the size of streams; the volume of water flowing past a certain point in a given time Competence - is a measure of a stream's ability to transport particles based on size rather than quantity.

Capacity

Explain the difference between capacity and competency.

Capacity is the maximum load of solid particles a stream can transport per unit time. (Large rivers with high flow velocities have large capacities) Competency is a measure of a stream's ability to transport particles based on size rather than quantity. (Swift streams have greater competencies than slow streams)

What are deltas? Where do deltas form? What are distributaries?

Deltas are areas where streams reach base level and deposit remaining sediments Distributaries carry water away from the main channel in order to get to base level in the event that sediments have become impassable

A dam and reservoir are constructed on a graded river. What will happen?

Deposition upstream from the dam; channel downcutting below

Describe how a stream's discharge, channel cross sectional area, velocity, channel roughness, and gradient changes when going from the stream's head to its mouth.

Discharge and cross-sectional area tend to increase towards the mouth of the stream Gradient tends to start of steep and becomes less steep towards the mouth Velocity increases with discharge

Which of the following factors do not influence stream turbulence and average velocity? Channel shape and bed roughness Dissolved load and water temperature above freezing Discharge (volume) and stream gradient (slope) Stream gradient and channel roughness

Dissolved load and water temperature above freezing How sodium dissolves in the water doesn't affect how fast the water flows

At the head of a delta, the major channel splits into smaller channels that follow different paths to the sea. These smaller channels are known as ________.

Distributaries

Over the oceans, evaporation exceeds precipitation, yet sea level does not drop. Explain why.

Each year, solar energy evaporates about 320,000 km of water from the oceans, but only 284,000 km return to the oceans as precipitation. A balance is achieved by the 32,000 km that carried to the ocean as runoff.

________ are components of the hydrologic cycle that release water vapor directly to the atmosphere.

Evaporation and transpiration

Gradients usually increase downstream in a major river system. True False

False, The higher the gradient value is, the steeper the slope is.

What causes floods? Identify and describe four types of floods? What are some of the ways that floods can be controlled?

Floods occur when water exceeds the capacity of stream banks and are caused by atmospheric processes 1. regional floods 2. Flash floods 3. Ice-jam floods 4. Dam-failure floods Floods may be controlled by artificial levees, channelization, or flood-control dams

How does urbanization (paving, etc.) affect runoff and infiltration in a small, previously forested, drainage basin?

Infiltration decreases while runoff increases

How does laminar stream flow differ from turbulent flow? What may cause laminar flow in a stream to change to turbulent flow?

Laminar flow- occurs in slow-slowing streams; water moves in nearly straight-line paths parallel to the stream channels Turbulent flow- water moves in an erratic flow with vertical and horizontal swirling motions Higher flow velocity and more path obstructions may result in a more turbulent flow

What causes a stream to deposit its sediment load?

Loss of velocity or reaching base level (also a form of velocity loss) will result in a stream depositing its sediment

How does a meandering stream channel differ from a braided channel?

Meandering channels- tend to carry lighter, finer sediments; one main channel meanders back and forth across landscape Braided channels- tend to carry coarser materials and discharge is variable; stream creates many, relatively small, interwoven channels across the landscape

Which of the following features characterize wide streams and valleys? Rapids and channel-bed potholes Waterfalls and entrenched meanders ( V-shaped valley cross-sections (most prominent features are rapids and waterfalls) Natural levees and broad floodplains

Natural levees and broad floodplains

Which one of the following statements is true concerning natural levees?

Natural levees are formed where the coarsest sediments are deposited adjacent to the channel during floods

How do natural levees form?

Natural levees- built by years of successive floods in meandering stream that occupy broad floodplains

Where is stream erosion concentrated along a meandering stream?

On the outer bank of a meander bend

Many larger rivers in the Colorado Plateau region meander in deep, narrow canyons and have no floodplains. How could this happen?

Original, old age streams downcut as the land gradually rose.

A(n) __________ is an abandoned, cutoff, meander loop. Back swamp - form in the low lands adjacent to the stream channel. As the floodwaters overflow the banks and natural levees, the water spreads out, the velocity drops, and the finer silt and clay settle on top of these marshy areas adjacent to the main supply source Divide - imaginary lines used to separate drainage basins. Point bar - A low, curved ridge of sand and gravel along the inner bank of a meandering stream that forms through the slow accumulation of sediment deposited by the stream when its velocity drops along the inner bank Oxbow lake - U shaped body of water that forms when a wide meander from the main stem of a river is cut off (abandoned), creating a free-standing body of water

Oxbow lake

Why is a bird-foot delta like that of the present-day Mississippi below New Orleans likely to change naturally toward one with the shape of an equilateral triangle like the upper-case, Greek letter delta (D)?

Potential, new, major distributary channels have steeper gradients than existing channels.

________ make up the suspended loads of most rivers and streams.

Silt and clay-sized, detrital grains

Which of the following make up the suspended loads of most rivers and streams? Silt and clay-sized, detrital grains Dissolved ions and sand Dissolved salts Sand and gravel that move during floods

Silt and clay-sized, detrital grains

How does the stream capacity differ from its competence? What major factor affects the capacity and competence of a stream?

Stream capacity- maximum load of solid particles a stream can transport per unit of time (greater discharge yields greater capacity) Stream competence- stream's ability to transport particles based on size rather than quantity (grater flow velocity yields greater competence)

What is meant by stream piracy? How does stream piracy create a wind gap?

Stream piracy- occurs when a stream, river drainage system, or watershed is diverted from its own bed, and flows instead down the bed of a neighboring stream A wind gap results as the former water way dries and leaves a gap in its place

Streams are vital geologic agents that perform four special functions. What are those functions?

Streams perform erosion and deposition

How does a stream respond to uplift of the land (erosion or deposition)? How does a stream respond to global sea-level rise (erosion or deposition)?

Streams will erode the land after uplift in order to get back to base level Streams will deposit their sediments in response to global sea-level rise

________ generally constitutes the highest percentage of the annual sediment load moved by a stream.

Suspended load 

How do stream terraces form?

Terraces- remnants of former floodplains

In the absence of cutoff, how does a river meander loop behave over time?

The gradient is lowered as the channel lengthens and migrates toward the cut or outer bank of the loop. 

What is the hydrologic cycle? Describe the different ways (e.g. infiltration, evaporation, runoff, and precipitation) by which water is transferred from one reservoir (e.g. oceans, glaciers, groundwater, etc.) to another.

The hydrologic cycle is the unending circulation of water between the hydrosphere, atmosphere, geosphere, and biosphere Infiltration- when water is soaked into the ground; absorbed by plants, stored in watersheds, etc. Evaporation- liquid water is converted into water vapor which moves about the atmosphere Runoff- occurs when ground is too saturated to allow for infiltration, or when surface is impermeable (concrete surfaces) Precipitation- occurs after water vapor in the atmosphere condenses to form liquid water; may infiltrate, freeze in a glacier, continue on as runoff, etc.

Define base level and distinguish between the ultimate base level and local, or temporary base level.

The lowest elevation to which a stream can erode its channel. Is the level at which the mouth of a stream enters the ocean, lake or trunk stream Sea level is the ultimate base level. local(temporary) base levels include lakes, resistant layers of rocks, and rivers that act as base levels for their tributaries.

Describe the movements of the hydrologic cycle. Once precipitation has fallen on land, what paths might the water take?

The water cycle is driven by heat energy by the sun. The sun warms up the water causing it to evaporates 320000km of water in the air. When precipitation falls on land, it either soaks into the ground (infiltration), flows to the surface (runoff), or immediately evaporates.

Most of the water is stored as glaciers and ice sheets? True or False

True

The lowest base level for most streams is sea level. True False

True

The stream gradient typically decreases downstream. True or False

True

Describe the two general types of stream valleys.

Valley deepening- downcutting of a stream creates deep, narrow valleys with steep valley walls Valley widening- broad floodplains are created by lateral erosion from meandering streams rather than vertical erosion

What is a water gap? Describe two ways by which a water gap may form in terms of antecedent stream versus superposed stream.

Water gap- a steep-walled notch followed by the river through a tectonic structure Antecedent streams existed before the uplift of land, therefore cutting the water gap into place Superimposed streams cut notch into place after uplifted structure already existed

What is meant by the term evapotranpiration?

a combined process of both evaporation and transpiration involving the transfer of water from the surface directly to the atmosphere

A river's flow velocity is primarily controlled by

discharge

Graded stream?

has correct slope and other channel characteristics necessary to maintain velocity required to transport material supplied to it and on average is neither eroding nor depositing material

What are the three principal ways by which a stream transports material? What is saltation?

in solution (dissolved load) 2. In suspension (suspended load) 3. Bed load (rolling/skipping sediments short distances along the stream bed) Saltation- sediment appears to jump/skip across the stream bed (short distances)

How does urbanization (paving, etc.) affect runoff and infiltration in a small, previously forested, drainage basin?

infiltration decreases; runoff increases

What is a Stream Terrace

mark former flood plains form when stream downcuts through previously deposited alluvium downcutting stream carves new, lower floodplain, leaving behind older floodplain as a terrance with significant downcutting, multiple terraces can result

What is the drop in water surface elevation divided by the distance the water flows? 

stream gradient

Stream gradient formula?

the drop in elevation of a stream divided by the distance the water travels gradient = (h1-h2)/l h1=altitude of the stream at point #1 h2=altitude of the stream at point #2 l=horizontal distance between points 1&2

A river's drainage basin is:

the total area from which its water flows and the discharge at mouth from the Mississippi River is 600,000 cubic feet

Which of the following is the only correct response concerning the location and causes of the extraordinarily severe, 1993, flooding on the Mississippi River and tributaries?

upper basin; very heavy, sustained rainfall in the late spring and early summer

What are three main parts (zones) of a river system?

zone of erosion, a zone of sediment transport, and a zone of sediment deposition

Correctly describe how stream terraces can form?

A temporary base level is eliminated; the stream downcuts upstream from the old temporary base level, and the former floodplain is left well above the present elevation of the stream.

What is an alluvial fan? How and where do alluvial fans form?

Alluvial fans are fan-shaped deposits that accumulate along steep mountain fronts due to the sudden decrease in stream gradient, causing streams to deposit high amounts of sediment

What type of terrain is characteristic of the drainage pattern shown below?

Alternating weak and resistant bedrock characteristic of folded terrain

The ________ river has the largest discharge of any in the world. 

Amazon

What type of stream pattern develops only on growing mountains like volcanoes or where the land surface is tectonically doming upward? Dendritic - commonly encountered with a "treelike" branching pattern that forms where the underlying material is relatively uniform. Because the surface material is essentially uniform in its resistance to erosion, it does not control the pattern of streamflow Radial - this pattern typically develops isolated volcanic cones and uplifts Rectangular - this pattern develops when the bedrock is crisscrossed by a series of joint and/or faults. Because the fractured rocks tend to weather and erode more easily than unbroken rock, the geometric pattern of joint guides the paths of streams as they carve the valleys Trellis - a rectangular drainage pattern in which tributary streams are nearly parallel to one another. This pattern forms in areas underlain by alternating bands of resistant and less-resistant rock and well displayed in the Appalachian Mountains.

Radial - this pattern typically develops isolated volcanic cones and uplifts

________ are characteristics of downcutting streams and a youthful stage of valley evolution.

Rapids and lots of whitewater

Which of the following features are characteristic of downcutting streams and a youthful stage of valley evolution? Rapids, V-shaped valley, and lots of whitewater Wide floodplains and meandering streams U-shaped valley profile with a wide base Natural levees and oxbow lakes

Rapids, V-shaped valley, and lots of whitewater

Which of the following must result in a lower base level for rivers and streams? Sea level drops; land subsides Sea level falls; land rises Sea level rises; land subsides Sea level rises; land rises

Sea level falls; land rises