GLG 171 Chapter 6: Streams
Atmosphere
0.001%
Soils
0.005%
Lakes and streams
0.015%
Ground water
0.63%
Glaciers
1.81%
What is the recurrence interval for a flood with a discharge of 1055 ft 3 / s that has a probably of occurrence of 4%?
1/0.04 = 25 years
What is a common lateral distance that meanders will migrate within a year?
10 meters
Consider a situation in which water usage rights for a large river were allocated to states based on an observation period. What length of observation period would be ideal?
100 years
The recurrence interval for a flood that has a probability of occurrence of 20% is ________ years.
5
Oceans
97.5%
Consider a situation in which a 100-year flood occurred in 2000. When could another 100-year flood occur?
Another 100-year flood could occur in any year after 2000, but the probability of this happening is low.
What defines a stream?
Any amount of water confined to a channel
Where is most sediment deposited in a stream-reservoir system?
At the top, where the stream meets the reservoir
Which points on this stream hydrograph show average conditions and flooding events in 1993 (red line)? (Select two that apply.)
C: Average flow A: Flooding event
What specific purpose does a dam provide?
Dams are used to moderate streamflow and prevent an excess of water from flooding downstream areas.
Which of these flood-control measures tends to create a false sense of security that results in potentially risky development of a floodplain?
Dams or reservoirs
Stream flow patterns may change over time. How might this affect the way data about streams is collected?
Data collected over a long period of time will be able to average a wide range of values.
Imagine a small town in 1973 with few residents and a stream flowing through it. A stream stage monitor has just been installed. By 2013, 40 years later, the town is well populated and hasn't flooded since 1973. What data about the stream might be lacking?
Data regarding severe floods, such as a 50- or 100-year flood, and an understanding of how large such a flood will be
Which of the following are methods used in channelization? (Select all that apply.)
Deepening Widening Lining Rerouting
How do deltas form?
Deltas form at the mouth of streams with high sediment loads. The sediment settles out when the velocity is reduced in a larger body of water.
Which of the following could cause a flood with a recurrence interval of 150 years to occur more frequently?
Development in the floodplain
What stream property is measured by cubic meters per second or cubic feet per second?
Discharge
What factors need to be considered when increasing flood-control measures? (Select any that apply.)
Does the cost of the flood-control measure exceed the cost of potential flood damage? What affect might the flood-control measure have on downstream sections of the channel?
Floodplains are the flat land that streams will fill with water when they overflow. How are floodplains formed? (Select the processes that apply.)
Downstream migration of meanders & Deposition of sediment during flooding
Which of these are common types of retention ponds that reduce flooding but do not alter stream characteristics directly? (Select all that apply.)
Fields dammed with dikes of soil Engineered structures Abandoned quarries
What type of graph is this showing the recurrence interval for various levels of stream discharge?
Flood frequency curve
What stream characteristics are monitored to create flood-hazard maps, which are used to minimize the risk of flood damage? (Select all that apply.)
Flood recurrence interval & Flood severity
Why is it important to project flood recurrence intervals and severity?
Flooding information is used to create flood-hazard maps.
What happened when the Atfchafalaya stream, a branch of the Mississippi River, was cleared of a natural logjam and opened as a diversion channel?
Flow down the Atchafalyaya increased so significantly that water available for navigation and sediment for the delta in the Mississippi diminished.
Which high-permeability surface will help reduce flooding by absorbing a lot of water in a large rainfall event?
Grasslands or prairie
Which of the following four areas of the United States most commonly experience floods from heavy rainfall events.
Gulf of Mexico Rocky Mountain streams West Coast Midwest
Traction load
Heavy debris moving on the bottom of the stream bed
Which of these parameters are used to calculate stream gradient? Assume that elevation 1 is upstream of elevation 2. (Select all that apply.)
Horizontal distance Elevation 1 Elevation 2
What are the benefits of flood-control dams? (Choose all that apply.)
Hydroelectric power can be generated. Water for irrigation can be stored. Streamflow can be moderated. Recreational facilities can be developed.
What are the main goals of channelization? (Select all that apply.)
Increase the volume of the channel & Increase the velocity of water flow
Which two characteristics in combination will cause stream flooding?
Increased water input & Limited channel capacity
Compare infiltration and percolation by selecting the correct description.
Infiltration occurs when water enters the soil, whereas percolation occurs when water moves through the soil underground.
What is a stream gradient?
It is the steepness of the steam channel.
Which of these can be a base level for a stream? (Select all that apply.)
Lake Ocean Larger stream
The number of stream gaging stations around the country are being reduced due to budgetary reasons. What might be a consequence of this?
Long-range data on stream flow may be lost in some locations.
What information that is interpreted from stream gaging data could be lost with continued decreases in the number of monitoring stations in the country? (Select all that apply.)
Long-term changes in discharge due to climate change Accurate discharge levels for floods of all sizes Accurate recurrence intervals for rare floods
Suspended load
Material that is moved along in the flowing water
Dissolved load
Materials that have dissolved in the water
How do meanders in streams form?
Meanders form when irregularities cause changes in water velocity that erode one side of the channel and deposit sediment on the other.
Imagine a uniform stream section with stage monitoring stations every mile for 10 miles. A hydrograph of the stream shows a peak corresponding to a new flood at mile marker 6. Will the hydrograph show the flood anywhere else? If so, where?
Mile markers 6 to 10
Assuming similar soil types, which type of terrain would allow the most water to infiltrate the ground?
Minimally sloped
When people removed a log jam on the Atchafalaya River in the 1840s, flow was diverted away from the connected __________ River. Now, the U.S. Army Corps of Engineers works to control the flow in the two rivers.
Mississippi
Water velocity in a stream varies based on many factors but is usually greater at the mouth than the head. Which part of a stream commonly has the highest gradient?
Near the stream head
The vast majority of water involved in the hydrologic cycle is located in the ________.
Oceans
As floodplains are developed, newly constructed buildings conform to the most current and rigorous standards. What happens to older, previously constructed buildings?
Older structures are left at risk because they do not conform to the most current standard.
What is an ephemeral stream?
One that flows occasionally
Which of the following statements best describes typical sorting within stream sediments?
Sediments are well sorted, with those of similar weights and sizes in a given location.
What storm water control device can increase the severity of flooding in streams by concentrating flow and decreasing the time taken for water to flow to a stream?
Storm sewers
What is the name of the chart that shows how the discharge of a stream changes over time?
Stream hydrograph
The country of Bangladesh occupies the last 7% of the Ganges-Brahmaputra-Meghna drainage basin; the remainder resides out of the country. What factors might the people of Bangladesh need to be aware of if a significant precipitation event occurred within the drainage basin?
Streams in the drainage basin may flood, and many in Bangladesh may have no forewarning.
Under what conditions does a braided stream form?
Streams with high sediment loads for the volume of flow divide across a broad area.
Which flood-control device has caused at least 10,000 small earthquakes in its vicinity?
The Hoover Dam
When a stream reaches its base level, the channel widens, the gradient is small, and the stream may flow more slowly. What happens to the discharge at the mouth of the stream?
The discharge of the stream usually increases as the channel becomes wider and carries more water.
Stream hydrographs with a long period of data over many years are useful because average stream flow on a yearly basis can be viewed. What distinguishes a flood from past data?
The flood is shown as a spike on the graph that is much higher than the average data.
What is the stage of a stream?
The height of the water surface at any point
How do oxbow lakes form?
The lakes form when large meanders are cut off during times of flooding, and the stream takes a more direct route.
Which of these reasons might result in the modern (human) development of a floodplain? (Select all that apply.)
The land is fertile. The land is flat. Floodplains can be very large.
Why are more dams being removed than new dams being constructed in the United States?
The negative effects of dams are better understood.
What is a recurrence interval for a stream?
The number of years between floods of a certain discharge for a particular stream
When a reservoir is created, it serves as a new base level for the stream. What effect does this have for the reservoir and the stream below the dam?
The stream dumps sediment where it meets the reservoir, and no new sediment is deposited below the dam, which prevents scouring.
Why are canyons, like this one shown, common locations for flash floods? (Select all that apply.)
The stream is confined. & The stream stage can rise rapidly.
What does a longitudinal profile of a stream show?
The stream's elevation from source to mouth
At what point has a stream crested?
The surface of the water has reached the maximum stage within the stream channel.
Which of the following describes an unfortunately common attitude toward development in the floodplain after a flood-control structure such as a dam is built?
The threat of flooding is gone, and development can safely be established anywhere downstream.
What is the capacity of a stream?
The total amount of material, or sediment, that a stream can move
Flood-control dams can be very effective but have specific disadvantages. Select all the disadvantages that may apply to dams or reservoirs.
The valley behind the dam is flooded. The valley downstream may still flood. River navigation is disrupted. Fish migration is disrupted.
At what water level has a stream begun to flood?
The water rises over the banks.
What are diversion channels used for?
They are used to redirect some water from a stream into an adjacent channel to reduce flooding of the main stream.
What effect do urban landscapes have on flooding?
They have a high percentage of impermeable surfaces, which increases flooding.
What is the purpose of a flood frequency curve such as the one shown?
To show the recurrence interval for a flood of a certain discharge
The National Weather Service and the ______ contribute data to create a flood prediction network around the country.
U.S. Geological Survey
Which of the following best describes upstream floods?
Upstream floods are small, localized floods.
Which of the following would cause a decrease in peak lag time and an increase in peak discharge, so that the stream would flood to a higher level more quickly than before?
Urbanization of the drainage basin
Which landscape feature can help reduce flood hazards by increasing soil permeability, reducing surface runoff velocity, and absorbing some water?
Vegetation
How does vegetation affect sediment transport in a stream?
Vegetation blocks sediment transport.
What causes the formation of an alluvial fan? (Select all that apply.)
Velocity decreases of tributaries meeting larger streams A stream flowing from the mountains into a plain
What are some disadvantages of levees being used for flood control? (Select all that apply.)
Water is moved downstream very quickly. Water that has overtopped the levee can't get back into the river. Levees give residents a false sense of security. Stage is artificially increased behind levee walls.
Which of the following are common negative effects of channelization to the environment and ecosystems? (Select all that apply.)
Water moves more quickly downstream. Habitat acreage may be reduced. Stream flow patterns are disturbed. Wetlands may be drained.
Is it possible that two 500-year floods could occur on a single river in two consecutive years?
Yes, although the probability is very low.
The hydrosphere is one of earth's four zones and contains ______.
all water on or near the surface
When a tributary stream flows into a slower, larger stream or a stream flows from the mountains to a plain, the decrease in velocity may create a(n) ______.
alluvial fan
The lowest point a stream can flow to is called the ________ _______ . For most streams, it is a lake or the ocean.
base level
More dams are ______ primarily because we better understand the negative consequences associated with them.
being removed than being built
When sediment load is high compared to the volume of water in a stream, the stream channels may divide to form a(n) _________ stream.
braided
The __________ of a stream is the total load of material or sediment the stream can move. It is related to the velocity of the water, which can move more material the faster the water flows.
capacity
Modifications to a stream channel that are intended to increase the velocity of flow and/or the volume of the channel are described by this general term:
channelization
Rerouting, widening, deepening, and lining are methods used for ________, which is done to increase the velocity of water flow through a channel.
channelization
When water is moved more efficiently downstream by efforts of ________ to increase stream velocity and increase channel capacity, the ecosystem suffers from loss of habitat, reduction of wetlands, and disruptions to stream flow patterns. Additionally, areas downstream of the modified section are more susceptible to flooding.
channelization
The benefit of flood control measures needs to be continually weighed with the ________ of building bigger and better structures. (Use just one word for your answer.)
cost
A stream has ____________, but not flooded, when the maximum stage is reached.
crested
A flood control measure meant to moderate stream flow and minimize flooding by partially blocking a stream is a(n) _________
dam
Creation of recreational lakes, storage of water for irrigation, and generation of hydroelectric power are additional benefits provided by the development of flood-control ______.
dams
Loss of navigable rivers for people and aquatic life and the intentional flooding of entire valleys are negative effects of building _________. (Use just one word for your answer.)
dams
Human development tends to ______ the recurrence intervals of high-discharge flood events.
decrease
Typically the average gradient of a stream ______, and in moist climates the average velocity ______, from the head to the mouth.
decreases; increases
The tan-colored sediment at the mouth of the Mississippi River in this picture is called a(n) __________, which forms when large amounts of sediment are carried to the mouth of a stream and deposited into a larger body of water.
delta
Stream _______ is defined as the volume of water passing a certain cross section, or slice, of a stream for a certain amount of time.
discharge
One method of flood control involves redirecting some stream flow into adjacent channels; these are called _______ channels.
diversion
Finer-grained sediments dominate the ______ area of a stream system.
downstream
When a large section of a stream floods, it is called a(n) _________ flood.
downstream
An area containing all tributaries and streams within a single network is called a(n) ___________ basin.
drainage
Aside from providing flood control, dams have been known to cause ______.
earthquakes
A stream that only flows occasionally is a(n) ________ stream
ephemeral
A rapid increase in stream stage in a restricted area with little to no floodplain would create a(n) ______ flood.
flash
A(n) _________-frequency curve shows discharge as a function of recurrence interval for a stream.
flood
A graph showing the recurrence interval of a flood with a certain stream discharge is called a(n) ________ ________ curve. These are useful graphs, as they can be used to estimate the size of rare floods such as 100-year events and for estimating the frequency of more common floods.
flood frequency
A stream in which water levels have exceeded the banks and flowed into surrounding land has __________
flooded
The processes of downstream migration of meanders over time and the deposition of sediment when the banks of a stream overflow create a flat expanse of land around a stream called a(n) ________
floodplain
Fertile soils, flat land, and wide floodplains are just three reasons that ______.
floodplains may be used for development
When water input into a stream is greater than the stream's capacity to carry that water downstream, the water overflows the banks. This happens when the stream _______
floods
The change in elevation of a stream divided by the horizontal distance the stream covers is the __________. Generally, the higher this is, the steeper the channel is.
gradient
A soil with ______ permeability, such as that found in a forest, will quickly absorb water during a rainfall event and limit flooding. Soils with ______ permeability, such as clays, may not limit the effects of flooding.
high; low
A graph showing stream stage or discharge over time is called a(n) ________
hydrograph
The U.S. Geological Survey monitors stream-stage measurements and data around the country. The National Weather Service collects data about historical and forecast precipitation. Together, the agencies create projected ______ to predict flooding.
hydrographs
All water found on and near earth's surface is included in the ________.
hydrosphere
Impermeable surfaces that concentrate storm water runoff can ______ flooding when they cover large areas in urban regions.
increase
Despite a decreasing gradient, discharge commonly _________ downstream because of water added by tributaries.
increases
Urbanization, specifically impermeable surfaces, increases the peak discharge of water in a stream, which ______ the stream's stage. Also, peak lag time ______ with growing urbanization and use of storm sewers.
increases; decreases
The process of water moving into the soil from rainfall is called ________. Whereas ___________ is the process where ground water moves through soil and rock.
infiltration; Percolation
A peak on a hydrograph that is wide represents a flood that ______.
lasted a long time
Which of the following equations represents stream discharge? (Length and width relate to the channel size whereas velocity is water flow.)
length×width×velocity
A stream underlain with bedrock experiences ______ sediment transport when compared to a stream bed made of sand and/or clay.
less
Raised banks along streams that increase channel capacity are called __________
levees
When the banks of a stream have been built up to be higher than the surrounding land, they artificially increase the stage of the stream. If one of these __________ were to fail, severe flooding may occur.
levees
A flood in an unmodified stream will deposit sediment outside the normal stream banks on the floodplain. When levees are constructed to confine floods, the sediment is deposited in the stream channel, which means that ______.
levees must be constructed higher or the channel must be dredged
This type of stream diagram is called a ______.
longitudinal profile
Which of the following units are used to measure stream discharge?
m3/s
When an irregularity in a stream channel causes erosion on one side of the channel and deposition of sediment on the other, a bend known as a(n) ________ will form.
meander
A meander might typically meander 10 ______ per year.
meters
The quantity of water on earth is ______.
nearly constant
Zoning restrictions used to mitigate floodplain risks often apply only to ______ buildings and leave ______ buildings at risk.
new; old
When a large meander in a stream is cut off due to increased discharge during flooding, the old meander channel forms a(n) _______ lake.
oxbow
Large basins that trap some surface runoff and delay it from flowing directly into a stream are called _________ ponds.
retention
Steep terrain causes water to ______ instead of ______.
run off; infiltrate
Levees must be continually built higher or the stream channel must be dredged because ______.
sediment from floods can no longer be deposited onto the floodplain, so it collects in the channel and increases the stage
The stream ________ is measured as the steepness of the stream channel.
slope
When stream velocity ______, larger sediment particles are deposited on the bottom on the channel, while lighter particles are carried with the water until velocity ______ again.
slows; decreases
From the point of origin of a stream to the mouth, sediments tend to get __________ in size.
smaller
The height of the water surface in a stream at any point is called the _________ of the stream. A stream has flooded and has reached flood _______ when the water has exceeded the height of the stream banks. (The same word goes in both blanks.)
stage; stage
A(n) _________ is any body of water confined to a channel.
stream
Storm sewers used to collect and redirect storm water flow are effective if ______.
the flow is low to moderate
The width of a stream channel is roughly proportionate to the volume of water ______.
the stream typically carries
The size of a stream channel is roughly proportional to ______.
the volume of water it carries
When floods occur in small, localized areas, they are sometimes called _______ floods.
upstream
Heavy particles are deposited on the bottom of a stream channel when water _________ decreases. Smaller particles will settle out of the flow with further decreases.
velocity
The destructive power of a flood comes from the combined power of the increased ________ and volume of water.
velocity
Floodwaters are destructive because of the increased ______, which produce a lot of force.
volume and velocity
The amount of ________ on and in the earth is fairly constant with occasional, small additions from volcanoes.
water
The amount of _________ on and in the earth is fairly constant with occasional, small additions from volcanoes.
water
Sediments tend to decrease in size from the source of a stream to its mouth. In any given location of a stream, these sediments tend to be ______, being of a similar size or weight.
well sorted
Saltation
A process in which material moves in short jumps along the stream bed
What is a 100- year flood?
A 100-year flood is a flood that will occur approximately every 100 years or has a 1% chance of occurring in any given year.
Which situation would benefit from an international flood forecasting system?
A coastal country contains the last 20 miles of a major river that resides primarily in a neighboring country.
Which of the following is the description of a cut bank?
A cut bank is the eroding side of a meander, or the outside edge.
What is a downstream flood?
A flood that occurs when a large section of a stream is affected
Which of the following is the description of a point bar?
A point bar is the depositing side of a meander, or the inside edge.
The flow of sand and silt in a stream, which is shown as A, is called ______. Heavy material rolling on the bottom of the stream bed, which is shown as B, is called ______.
A: suspended load; B: traction load
How does vegetation help mitigate flood hazards? (Select all that apply.)
Absorbs water Increases soil permeability Reduces water velocity
Bed load
All material moved along the bottom of the stream
Rare floods, such as 100-year events, have a certain probability of occurring in a given year. However, floods for many streams are not well understood. Why?
Reliable records of rare floods are not available for many streams, so an exact understanding of such a flood's recurrence interval is unknown.
Between restrictive zoning in floodplains, levees, and dams, which flood-control measure should have the best results against flood risk over the broadest area?
Restrictive zoning
What is the best method of defense against the risk of flooding?
Restrictive zoning that limits development in a floodplain
Repurposing old quarries or damming fields with piles of soil are inexpensive ways of creating _________ ___________ that reduce flooding from surface runoff but do not alter stream flow.
Retention ponds
Which of the reservoirs of the hydrologic cycle has the shortest residence time?
Rivers