Chapter 16: Streams and Flooding

What problems are associated with straightened or channelized stream channels?

-Increased erosion downstream -Downstream flooding -Reduced sediment deposition downstream

From the list below, select the factors that control the deposition of a delta.

Discharge Vegetation Sediment load Wave action River and ocean ice

What happens to the erosive power of a river as velocity increases?

Erosion increases.

Select all the natural causes for flooding from the list below.

Eruption of snow-covered volcano Regional precipitation Snowmelt Local heavy precipitation

Rank the following particle sizes transported by water from smallest to largest. (Place the smallest particle size at the top.)

1. clay 2. silt 3. sand 4. cobbles 5. boulders

The 1993 flood of the Mississippi River at St. Louis began June 26 when the river reached the flood stage, and peaked August 1st. The flood peak was about _______ feet above flood stage.

20

If you examined a hydrograph and saw peak discharge in a small amount of time, then a quick decline in discharge, what might have been a possible explanation for the peak?

A heavy rainstorm event upstream

One stream may divert the flow of another stream into a different basin through the process of stream _______ . This occurs during _________ erosion

Blank 1: capture Blank 2: headward

Select the answer that is not a factor in the deposition of deltas.

Chemical makeup of sediment

Steep slopes in a(n) narrow canyon plus an unusually large thunderstorm resulted in the 1976 Big Thompson River flood near Estes Park in the state of _____ , just outside of Rocky Mountain National Park.

Colorado

Which of the following is not a characteristic of a braided river or stream?

Constant flow

Select the human-caused flooding events from the list of flood causes below.

Dam failure Urbanization

Select the conditions that caused the 1976 Big Thompson River flood near Estes Park, Colorado.

Narrow canyon Steep slopes of the river canyon Unusually severe thunderstorm

A tributary that itself has a tributary within a drainage system is a(n) ______-order stream.

Second

Which of the following physical parameters show an increase from the headwaters to the mouth of a river?

Sediment load Discharge Channel size

Select common features located along low-gradient rivers.

Single channels River terraces Meanders Floodplains

What is a drainage basin?

The naturally defined area that a stream drains

When are stream eddies formed?

When turbulence increases

This is a natural

arch

Bedrock channels occur where erosion by a stream has cut down into the local bedrock. Although erosion is the dominant process, ______ tends to occur where and when flow velocity decreases. Lower velocities can often be found behind objects, such as boulders, in the stream.

deposition

The volume of water flowing through a stretch of a river is the _____ and is measured by multiplying the river depth by river width and river velocity.

discharge

What is the name for small, branching channels that carry water away from the main river channel and distribute it over the surface of the delta?

distributaries

The production of ice sheets during global cooling results in _____ sea levels. These ice sheets can depress the _____ , causing river drainages to flow toward the ice sheets.

lower; crust

A flash flood ______.

often results from intense rainfall lasts a short time

A river cannot erode below ______.

sea level

Construction of dams causes an interruption of river flow. River ____are deposited upstream of the dam, shortening the life of the reservoir.

sediments

The turbulence of water increases as the water's ______ increases, which can increase the water's ability to erode and transport materials within the channel.

velocity

Rank the following events in order to explain the formation of a natural arch, placing the beginning event on top and the final event on bottom.

1. layers of strong rock are present 2. parallel, vertical joints develop in rock layers; weathering attacks the surface area exposed by the jointing 3. notches form where joints are located; notches capture and channelize water to increase erosion 4. landscape becomes narrow fins of rock, flanked by lower, more eroded areas and isolated knobs. 5. Part of a fin falls due to gravity, and an opening forms in the rock. 6. the opening grows larger and becomes more arch-shaped

What is a floodplain?

A broad strip of land built up by sedimentation on either side of a stream channel and covered with water during a flood

The formation of a natural arch requires which of the following?

A strong type of rock The formation of fins Erosion by water and/or wind

The image shows a stream hydrograph of a flood where discharge is on the vertical axis, time is on the horizontal axis, and the red line is the flood stage. Which labeled point shows where the flood begins?

B, where the stream rises to the flood stage

In mountain streams that are steep with high stream velocities, which pattern of erosion is the most common?

Channel bed is eroded faster than the channel sides.

In which location would a geologist look for a river confined to a single channel?

Gentle plains

What is happening to coarse-grained sand in a stream velocity of 70 cm/s?

It is being transported as bedload.

What is happening to silt and clay in a stream velocity of 5 cm/s?

It is being transported as suspended load.

Which of the following describe the largest known flood along the Colorado River?

Its discharge is estimated using geomorphology. It had a discharge of approximately 8,500 m3/sec. It occurred before humans were in the area.

Which two drainage divides are separated by the Continental Divide?

Pacific Ocean Gulf of Mexico

What occurred to decrease the gradient of the Lower Mississippi River, causing it to deposit sediment within the valley it has previously incised?

Sea level rose.

Which of these has a concave-up shape?

Stream elevation profile

A decrease in the size of sediments carried by a river usually reflects ______ in the gradient of the river.

a decrease

When steep, narrow drainages enter broader, more gentle valleys and streams deposit the large sediments they are carrying,

alluvial fans

A stream ______ erode below its base level.

cannot

Rivers on gentle plains usually occupy a single ______ rather than being braided.

channel

In a meandering river, the deeper outside bend is eroded into a steep riverbank referred to as a(n) ______ , and on the shallower opposite side of this is a(n) ______ bar

cutbank, point

As the gradient decreases in a river, the size of the sediment that can be transported

declines

The feature formed when a river deposits its sediment near its mouth is a(n) ______.

delta

The drainage pattern associated with areas where the rocks have the same resistance to erosion is a

dendritic, radial

A stream with no tributaries is a ______-order stream.

first

An event in which the amount of water flowing through a river channel overflows its banks is a(n)

flood

Human-constructed barriers such as levees are beneficial because they can help prevent _______; however, it is difficult to construct an affordable levee that will not fail during the worst situations.

floods

As meanders develop on a floodplain and either the base level drops or a tectonic event causes uplift, the meanders deepen and become

incised

Streams that have cut down into bedrock and flow through bedrock channels are called ______ streams.

incised

Match the feature with its description. Instructions

natural arch - A large opening that goes all the way through a narrow panel of rock. Begins with the formation of joints. fin - A narrow panel of rocks that is the result of weathering controlled by joints on both sides window - A small opening that goes all the way through a narrow panel of rock

Changes in water or sediment supply, change in slope, or changes to base level elevation can begin or end the life of a(n)

river

The Salton Sea in California was formed in 1905 when ______.

the Colorado River flooded

True or false: Increasing the rate of runoff increases the likelihood of flooding in local streams.

true

Where is the peak discharge on this hydrograph?

B

What is a natural bridge?

An arch-shaped features that span a (former) stream

The red line marks the ____ Line, the boundary between hard bedrock in the mountains and soft sediments in the coastal plains. Stream gradient changes here, and it is marked by a series of _____

Blank 1: Fall Blank 2: waterfalls

Lake Mead and Lake Powell were created by damming the

Colorado river

Select from the list below the two large reservoirs created by damming the Colorado River.

Lake Powell Lake Mead

Which of the following are primary factors that influence a stream's profile?

Tectonics Climate Rock type Sea level

What is the name of the subsidiary channels that join up with the main river channel?

Tributaries

Multiplying the width of a channel by its average depth will give you the ______ of the channel

area

Streams are systems driven by ______.

precipitation and gravity

The size of the drainage basin and the ______ the drainage basin influence the flow response to rainfall.

shape of

When comparing their ages, the Upper Mississippi is _____ than the Lower Mississippi.

younger

What characteristics do rivers and streams share?

-They can be braided or meandering. -They flow within a channel. -They flow downhill due to gravity.

Use the following information to calculate the gradient of River X. If the vertical change is 20 meters in 1 kilometer, then the gradient expressed in m/km is ______.

20

What is a bedrock stream?

A mountainous stream flowing through a carved bedrock channel

What is a stream terrace?

A stream terrace is an old floodplain perched outside and above the current floodplain.

What is a braided stream?

A stream that flows in a network of many interconnected rivulets around numerous bars.

These are formed when a steep drainage enters a broad valley and the sediments and debris are deposited.

Alluvial fans

The Fall Line is located between the ______ Mountains and the coast, and is marked by ______.

Appalachian; waterfalls

Over the last 7,000 years, the mouth of the Mississippi River has moved. What evidence supports the different end points of the river?

As least six huge abandoned sediment deposits mark where the river created a delta.

Select conditions that have an effect on the flow of river systems over time.

Dams Geology Climate Tectonism Runoff

______ are formed as rivers slow down when they reach their mouth and empty into an ocean.

Deltas

Match the location of the diagram with a description of the shape of the river.

Left - braided Middle - low sinuosity right - meandering

The Colorado River starts in the Rocky Mountains in the United States and has its mouth in

Mexico

What are distributaries?

Small, branching channels that carry water away from the main channel

From the list below, select the characteristics of a braided river or stream.

Steep gradient Variable flow Abundant sediments

What process generally defines a nickpoint and forms waterfalls?

The channel bed below the nickpoint has a faster erosional pattern than above the nickpoint.

A community experiences two floods with stream discharge equal to the 100-year recurrence interval. The floods occur in 1980 and 1990. When will or did the next flood occur?

The next 100-year flood could occur in any year.

Which two of these do you multiply to determine the discharge of a river?

Velocity of the river Area of the river

Select the three measurements needed to calculate discharge of a river at a certain point.

Velocity of the water River depth River width

What is a flood?

Water overflows a stream's channel.

A broad strip of land on either side of a stream channel that is covered by water during a flood and replenished by sedimentation is a(n)

floodplain

Viscosity is the resistance to ____ exhibited by fluids.

flow

The driving force behind a river's flow is ______.

gravity

A cutoff meander may develop into a(n)

oxbow

Older floodplains that are perched above current floodplains are called stream

terraces

How can the melting of an ice sheet or glacier affect a river's drainage?

-Melting of the ice releases tremendous amounts of water and sediment that lead to new or larger channels. -Uplift of the land after the glacier melts can change drainage patterns and direction.

Which of the following are ways in which tectonism, such as an uplift of a mountain, can affect drainage?

-The uplift can increase the supply of coarse sediment. -The uplift can increase precipitation into the drainage. -The uplift can increase the slope of the drainage. -The uplift can cause a rain shadow on the other side, causing a decrease in the runoff into the drainage.

On a field trip, you measure the following: river depth = 7 feet; river width = 12 feet; and river velocity = 3 feet/sec. What is the discharge?

252

Match the phrases to describe how a stream profile is influenced by changes in its environment.

A drop in base level - will result in more downcutting. An increase in rainfall - will increase discharge and sediment load capacity. Subsidence in the mountains - will flatten gradient, causing deposition

The discharge of a river is measured in cubic ____ per second

feet

The Upper Mississippi River ______.

was created by glacial meltwaters is young

Changes in the ______ can begin or end the life of a river.

water or sediment supply at the source slope the river flows across elevation at the base level

A nickpoint is a location where a stream has an abrupt change in gradient and can form a(n)

waterfall

A stream deposits the sediment it is carrying ______.

when it no longer has the capacity to do so

Do changes in tectonics, human development, and geology affect river systems?

yes

Rank the following in order to describe the formation of a natural bridge, placing the beginning event on top and the final event on bottom.

1. A meandering stream carves a curved canyon from a landscape. 2. Entrenched meanders are formed as the stream erodes into deeper layers of rock. 3. The river erodes laterally to make rock between entrenched meanders thinner. 4. The river cuts through ridges between meanders and alters its original path. 5. A natural bridge is formed along with an abandoned meander.

Order the sequence of layers produced as a delta builds out into the oceans from flowing rivers, as you would see them in a cross section.

1. horizontal beds deposited partly on land 2. cross-bedded sediments 3. marine clays

Summarize the formation of a natural bridge by matching the locations with the process most likely to occur there as the river continues to erode the surrounding rocks.

1. natural bridge 2. abandoned meander

The process of meander formation begins when a difference in roughness on the ______ causes water to move faster on one side of the channel than on the other.

Bottom

______ are formed as flowing water collects in natural cracks or low spots. Once formed, these capture additional runoff within the drainage basin.

Channels

Which large river runs from the high Rocky Mountains to western Mexico passing lakes, dams, reservoirs, geologic structures, incised meanders, and finally a delta on its journey? The

Colorado

Why do the meanders on a stream migrate?

Continuing erosion and deposition

Which of the following are considered to be causes for severe flooding events other than precipitation alone?

Failure of a dam Stalled hurricane Rainfall coinciding with snowmelt and ice dams in a river Prolonged drought followed by intense precipitation

Match the factor or process with how it influences or changes a stream profile.

Flow over unconsolidated sediments - Stream profiles are smooth, as these are easily eroded. Tectonic uplift - This causes stream to incise into the landscape. Rise in sea level - This causes the stream to deposit sediment along the coastline.

Features that occur along the Colorado River include ______.

Lakes, Geological structures, Dams, Lava flows

What types of streams typically deposit clay- to sand-sized sediments?

Low-relief streams

The part of the Mississippi River that carved itself a river valley over Cenozoic sedimentary rocks when sea level was low, and then filled the valley with deposits when sea level rose, is the

Lower

Which of the following physical parameters show a decrease from the headwaters to the mouth of a river?

Maximum grain size

During the 1993 flood on the upper _____ River, floodwaters flowed onto the floodplain because levees did not hold the water back. It took months for the floodplains to dry out because the _____ trapped the water, preventing it from flowing back into the river channel.

Mississippi; levees

______ are formed beside low-gradient rivers when floods occur and sediments build up along the channels. These features become barriers to water returning to the river from the floodplain.

Natural levees

On the diagram shown, look at the channel profile at the place labeled "cutbank." Where is the deepest water? The shallowest water?

On the outside of the bend; on the inside of the bend

What is an incised stream?

One that has eroded into the underlying rock

How long was the Mississippi River above flood stage in St. Louis during the summer of 1993?

Over 3 months

What types of sediments or rocks are deposited by low-relief streams?

Sand Silt Clay

Which of these would indicate a flood on a stream hydrograph?

Stream discharge that is greater than the flood stage for the channel

Match the river drainage pattern with the appropriate description of its geology.

Structurally controlled pattern - Drainage occurs on eroded layers or structures and then cuts across a ridge to follow a different weak layer. Radial drainage pattern - Drainage is found on symmetrical mountains such as volcanoes. Dendritic drainage pattern - Treelike pattern develops on rocks with similar resistance to erosion.

The flat benches that are perched above a river or stream and that stair-step upward and outward from the active channel are

Terrace

Select consequences to a river when a dam is constructed.

The dam causes the river to deposit its sediment load upstream of the dam. The dam creates a temporary base level for the river. Water released from the dam is clear (no sediment) and has a new capacity to erode and transport sediments downstream.

When conditions such as climate remain stable, a river may approach a dynamic equilibrium state. The river would then be considered ______.

a graded stream

Geologists use large water tanks in laboratories to study braided river dynamics. They control the slope, the ______, and the consistency of water flow to study how the variables affect the stream system.

amount and type of sediment

Streams that are associated with and predate the formation of a geologic structure are ______, whereas a stream that is established in association with but after the formation of a geologic structure is ______.

antecedent; superposed

Compare antecedent and superposed streams by matching them to their correct descriptions.

antecednet - A stream incises as geologic structures in and around it change and form while the stream stays in the same place. superposed - A river incises into soft sediment, and becomes trapped in its own canyon as it encounters geologic structures.

The headwaters of the Colorado River ______, and the mouth is at the Gulf of California.

are in the Rocky Mountains

The area that a stream naturally drains is called a drainage

basin

Flat-bottomed valleys between mountains would be good places to look for ______ rivers or streams.

braided

The type of rivers that are characterized by a network of interweaving sinuous channels, with the overall channel being fairly straight, are _____ rivers

braided

As water flows, it accumulates in natural cracks, which eventually form ______ rather than spreading across the land.

channels

Most streams have ______ profiles.

concave up

The feature that is formed where a river meets the sea, slows down, and deposits its sediments is a(n)

delta

When rivers enters a lake or an ocean, they slow down and lose their capacity to carry sediments, forming ______.

deltas

Soluble materials in flowing water are removed and transported by a process called ______.

dissolution

As the velocity of water increases so does the turbulence. This results in the formation of swirls in the current called

eddies

Acting as major sculptors of Earth's surface, rivers and streams ____ the landscape, carry the materials, and later deposit the sediments.

erode

On the outside of a meander, the water velocity is faster and causes ______, and on the inside of a meander, the water velocity is slower, which causes ______.

erosion; deposition

True or false: The position of the Mississippi River delta has been remarkably stationary for the past 7,000 years.

false

Meanders cause differences in water velocity in the river channel. On the outside of a meander, water velocity is ______ and causes erosion, while on the inside of a meander, water velocity is ______ and deposition of sediments occurs.

faster; slower

Large water tanks in laboratories are used by geologists to study water ______ in river systems because the tanks can be used to control the slope of the river and the type of sediments.

flow

In flowing water, the upstream side of an obstruction is subjected to the ______ of abrasion.

greatest amount

Streams can expand the area of the basin by ______ which may lead to ______.

headward erosion; stream capture

The area of the origin of a river is its ______, and the ______ the end of the river.

headwaters; mouth is

Channel beds erode faster than the channel sides in ______ streams and rivers. These are generally steep mountain streams.

high-gradient highly turbulent high-velocity

The more years of river flow data that are collected, the ______ the probability of predicting a major flooding event.

higher

The ______ the velocity of a river, the ______ its capacity to carry sediment.

higher; larger

The probability that a discharge of a certain size will occur during any given year is calculated using ______.

historic raw data

The uplift of high mountain ranges increases slope and precipitation causing a subsequent ______ in the amount of sediment available for a stream to transport.

increase

The estimates for a 100-year flood on the Colorado River near Lee's Ferry are based on ______.

inferred discharge of historic floods

When a river floods and deposits sediment parallel to and along the river channel, a(n)

levee

Flooding can be prevented by building _____ parallel to river channels. However, these structures do fail, and construction to prevent the worst possible flooding events is not affordable.

levees

A delta is formed where a river meets an ocean because _____ is deposited as the river loses speed.

load

Meanders, floodplains, and river terraces are commonly found along

low

Braided rivers carry more volume and larger size ranges of sediment types than

meandering

Because of continued erosion and deposition that leave behind scars and point bars, river _____ migrate back and forth across a flat valley floor.

meanders

The size of sediments in braided rivers typically is ______ than that carried by meandering rivers.

more varied

A large opening that goes all the way through a narrow panel of rock is called a ______. A smaller, but similar opening is called a ______. These features may form in areas where a narrow panel of rocks, called a ______, has formed due to weathering controlled by joints on both sides.

natural arch; window; fin

When meander scars are filled with water, they are ______.

oxbow lakes

A stream or river that flows all year is ______.

perennial

A stream that flows year-round is a(n) ____ stream, whereas a(n) ___ stream does not flow the entire year.

perennial, ephemeral

Potholes or bowl-shaped pits are formed when flowing water and sediments swirl in small ______ in the rock.

pits

A depositional feature that has been built on the inside of a stream channel curve because of lower velocity is a ______.

point bar

The ability to determine the ______ of a flooding event is based on river flow data. The more data collected and the greater the time span for data collection, the better understanding we have of the chance of future flooding events.

probability

The movement of sand grains by a series of short leaps or bounces along a streambed is

saltation

Meandering rivers leave behind exposed curved ridges called meander _______ marked by lines of vegetation or as curved dry depressions. When the depressions are filled with water, they are ______

scars; oxbox

The ______ load is the total amount of sediment carried by a river.

sediment

Slope failures from the surrounding mountain slopes and tributaries are the two sources of ______ in mountain streams.

sediments

The particle size transported by water that is in between clay and sand is

silt

When a river enters an ocean and begins depositing sediments to form deltas, the first particles to settle out are large particles and sand followed by

silt; clay

The gradient, or ______ of a stream is steeper near the headwaters than at the mouth.

slope

With respect to the seasons, the highest discharge of a river in the Upper Midwest is usually in the ____ and the lowest discharge is during the

spring, winter

We disrupt the balance of a river system when we discourage the process of migration and meandering by ______ streams.

straightening

Rivers and streams are similar bodies of flowing water. A(n) _____ is a body of water with a current that flows downstream within a channel. A(n) _____ is a large body of water with considerable volume and permanent or seasonal flow.

stream, river

a river _____ is formed as a river incises into the surrounding rocks and sediments, abandoning the floodplain and leaving a record of the river's historical size and location.

terrace

The formation of the Salton Sea occurred in 1905 during a flood of the Colorado River. It occurred in an area ______.

that historically had a lake

Sinuosity refers to

the amount that a river or stream channel curves in a given length

A hydrograph shows

the change in a river's discharge over time

Waterfalls, lakes, and large boulders are landforms that characterize ______.

the headwaters of mountain streams

The term "100-year flood" signifies ______.

the size of a flood that is predicted to have a 1 in 100 probability of occurring in a given year

When the gradient of a stream steepens or the channel is constricted by bedrock or obstacles, the flow of water becomes ______ forming ______.

turbulent; rapids

Many historic floods are associated with the large precipitation that accompanies a(n) ____ ; a good example is the storm named Mitch in 1998 that brought 78 inches of rain in some places in a few days.

typhoons

The graphs geologists use to estimate river flow probability are ______.

unique to each stream