GEO101 Module 6 Connect Part 2
What steps are taken to restore a wetland?
Ditches and canals are filled in. Water sources are reconnected. Levees are removed.
What type of flood affects lower areas of the drainage basin and inundates wide areas of the floodplain and valley floor?
Downstream flood
What has caused widespread changes to stream hydrology, including flooding frequency and severity, over the course of the last few decades?
Human development
True or False Question True or false: The function of wetlands is poorly understood scientifically, but wetlands have little impact ecologically or on the severity of flooding.
False
Which of the following are common negative effects of channelization to the environment and ecosystems?
Floodplain ecology is altered. A higher volume of water is moved downstream.
What are flash floods or upstream floods?
Floods that quickly overflow the banks of the streams, typically from intense rainfall filling small stream channels
Order these rivers with those having the highest discharge based on climate and drainage basin size at the top and those with the lowest discharge at the bottom.
1.amazon 2.congo 3.mississipi
Click and drag on elements in order Order the steps of natural levee formation from first at the top to last at the bottom.
1.stream velocity and discharge 2.bed load 3.water level increase 4.velocity reduces 5.sediment is deposited
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 to understand how the river behaves?
100 years
Which of these precipitation events is most likely to cause a flood?
3 inches of rain over 4 hours
Which of these hydrographs best represents a flash flood?
A
Match the zone labeled on the map with the description of where it fits in the floodplain.
A matches Choice, NFIP floodway; critical zone for flood risk where development is severely limited NFIP floodway; critical zone for flood risk where development is severely limited B matches Choice, Flood fringe; restricted zone for development where flood risk is fairly high Flood fringe; restricted zone for development where flood risk is fairly high C matches Choice, Regulatory floodplain; the area where the relative flood risk is higher than the rest of the landscape Regulatory floodplain; the area where the relative flood risk is higher than the rest of the landscape
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.
The lowest point a stream can flow to is called the . For most streams, it is a lake or the ocean.
Blank 1: base Blank 2: level
Sediment pollution controls that aim to trap soil include stream that use vegetation to limit soil erosion and fences, which are synthetic fabric sheets that trap sediment but allow water to pass.
Blank 1: buffers Blank 2: silt
If two streams have drainage basins equal in size, differences in their discharge would be due to their
Blank 1: climate, precipitation, rainfall, or moisture
The most significant effect of urbanization on streams is the spread of impermeable surfaces. Precipitation is not allowed to the landscape and is forced to move as overland flow.
Blank 1: infiltrate
The movement of large quantities of soil off the land and into drainage systems is called sediment
Blank 1: pollution
Houston has long experienced floods due to the natural setting of the city and associated with human actions. The floods have become more frequent and more intense in the last 20 years, likely due to a climate.
Blank 1: warming or changing
Which zone on this map is a drainage basin?
C
What is the most likely factor that Houston has experienced such frequent, large floods in the last 20 years?
Climate change
Why have people historically built settlements near streams and in floodplains?
Close proximity of water Source of energy Source of food
What specific purpose does a dam provide?
Dams are used to moderate streamflow and prevent an excess of water from flooding downstream areas.
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.
What is the effect of channel sedimentation on flooding?
It increases the frequency and severity of flooding.
What is a stream gradient?
It is the steepness of the steam channel.
Why is floodway management the best approach to handling floodways in communities?
It reduces the amount of development in the floodplain, damage costs are much lower, and recreation areas can be developed.
What are some disadvantages of levees being used for flood control?
Levee channels cannot hold as much water as floodplains. Stage and flood risks increase for sections upstream and downstream. Stage is artificially increased behind levee walls.
Which of the following are causes for artificial levee failure?
Levee saturation and water infiltration Cracks or holes in levee walls Flood waters breaching levee walls
What drainage basin characteristics aid in the formation of stream meanders?
Low gradient Wide valleys Decreasing water velocity
Which of these reasons have historically led to the drainage of wetlands?
Mosquito-breeding habitats Blockage to human travel Saturated soils
Which of the following are characteristics that make a channel susceptible to flash floods?
Narrow channels High water velocity Minimal floodplain formation
What program allows home and business owners with properties in floodplains affordable access to flood insurance?
National Flood Insurance Program
Why are floods difficult to predict?
Projections are based on statistical probabilities.
What are the benefits of flood-control dams?
Recreational facilities can be developed. Streamflow can be moderated. Hydroelectric power can be generated. Water for irrigation can be stored.
What is the best method of defense against the risk of flooding?
Restrictive zoning that limits development in a floodplain
What is the flood-control device shown here?
Retention pond
How does construction activity exacerbate flooding?
Sediment is deposited in channels. Overland flow increases. Vegetation is removed.
Which of the following are the two primary methods used to reduce sediment pollution?
Soil particles are kept in place. Physical barriers trap sediment outside the drainage network.
What is the primary function of a floodplain?
Storing water
What is infiltration capacity?
The ability for the ground to absorb water and reduce overland flow and flooding
What indicator may be present if a stream experiences multiple floods with 100-year or greater recurrence intervals in a short period of time?
The frequency of recurrence interval may indicate a change in climate.
What is the stage of a stream?
The height of the water surface at any point
What is the source of the large quantity of sediment polluting streams?
The landscape
What is a recurrence interval for a stream?
The number of years between floods of a certain discharge for a particular stream
What is lag time?
The time it takes for overland flow to reach a channel
Flood-control dams can be very effective but have specific disadvantages. Select all the disadvantages that may apply to dams or reservoirs.
The valley downstream may still flood. River navigation is disrupted. The valley behind the dam is flooded. Fish migration is disrupted.
Which flooding type poses the greatest risk of loss of life?
Upstream flooding
How does urbanization affect groundwater?
Urbanization can reduce the quantity of water that is able to infiltrate and permeate to the aquifer.
Channelized streams are characterized by smooth, straight channels, as shown in the picture. What features are characteristics of natural streams?
Varying water depth Plant and animal habitat Varying velocities
Which landscape feature can help reduce flood hazards by increasing soil infiltration capacity, reducing overland flow velocity, and absorbing some water?
Vegetation
Removing vegetation can worsen flooding conditions in drainage basins. What function is the vegetation serving?
Vegetation intercepts water on its leaves and increases soil permeability.
The value and function of wetlands are fairly well understood. They are dynamic systems that offer critical functions in the ecosystem and specifically in drainage networks. How are wetlands approached for development?
Wetlands are valued as natural land and protected for their ecological and flood control functions.
Natural levees are formed when ______.
a river floods and deposits sand adjacent to the banks
The government regulatory definition of floodplains includes ______ where the floodplain ______ well developed. The natural definition of a floodplain includes only sections of the stream with flat areas of land adjacent to the stream.
any land; may not be
A 25-year flood has a recurrence interval of 25 years and will occur ______.
any time
Residents living in floodplains must consider the likelihood of a catastrophic flood that could occur ______ and the ______ associated with flood-proofing a home.
at any time; high cost
Modifications to a stream channel that are intended to increase the velocity of flow, the volume of the channel, and the discharge capacity are described by what general term?
channelization
Flooding is aggravated by ______ activity, which removes vegetation and increases overland flow. Streams can quickly fill with ______.
construction; sediment
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
Typically, the average gradient of a stream ______, and in humid climates, the average velocity ______, from the head to the mouth.
decreases; increases
Houston's reservoirs were built to control flooding when the city had 800,000 people. Now with over 10 times that number of citizens, the effectiveness of the reservoirs is ______.
decreasing
Floodway management can benefit communities by ______.
developing public spaces that everyone can use prohibiting buildings that would likely be damaged
Construction of levees often causes water to back up upstream and leads upstream communities to build their own levees. Water levels tend to rise higher in the ______ levees. Higher water levels cause greater stress on or failure of the structures when they are ______.
existing; saturated
A(n) occurs when the amount of water in a stream is more than the channel can carry and the water spills over the banks.
flood
When a stream receives more water than it can carry and overflows its banks, the stream has ______.
flooded
Which of the following units is used to measure stream discharge?
ft3s
Urbanization leads to ______.
more flash flooding more severe flooding
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
When stream velocity ______, larger sediment particles are deposited on the bottom on the channel first. If velocity ______ downstream, lighter particles are the first to be carried with the water.
slows; increases
There are two primary methods used to reduce sediment pollution. First, an effort is made to keep ______ in place. Second, a physical barrier is used to trap sediment before it can enter the drainage network.
soil grains
When we quantify a flood by measuring how high the river is compared to a reference, we are measuring the ______. We can also measure a flood by its ______, or the volume of water flowing past a given point.
stage; discharge
A stream that exists within a narrow valley and has little to no floodplain is ______ to flash flooding.
susceptible
The levee effect describes _____
the false sense of security of living in a floodplain protected by an artificial levee
Following the 2005 flooding disaster in New Orleans, the costliest in U.S. history, and one in which nearly 2,000 people died, ______.
the government approved over $14 billion to improve flood controls for the city
Floods are difficult to predict because their recurrence is estimated by statistics, and ultimately, they are dependent on ______ instead of ______.
weather; climate
Meandering streams are characterized by ______ valleys with ______ gradients.
wide; gentle
In the hydrologic cycle, precipitation reaches groundwater through or is part of overland flow that runs off into streams.
Blank 1: infiltration
The ability for the ground to absorb water is called capacity.
Blank 1: infiltration
The time it takes for runoff to reach a stream channel is time.
Blank 1: lag
Much of New Orleans is situated in a bowl-shaped depression that is below sea level and is protected by artificial ; these are the features that broke in the disastrous flooding of 2005.
Blank 1: levees
Question Mode Fill in the Blank Question Fill in the blanks to complete the sentence. 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.
Blank 1: levees
Raised banks along streams that increase channel capacity are called
Blank 1: levees
Why does the widespread removal of wetlands cause an increase in flooding?
Wetlands provide temporary storage of floodwaters. Without wetlands, the water expands wider through the floodplain.
Stream buffers and silt fences are two of the primary methods used to reduce sediment pollution. Match the method to its common application.
Stream buffers matches Choice, Reducing erosion from logged or agricultural land Reducing erosion from logged or agricultural land Silt fences matches Choice, Reducing erosion from lots under construction Reducing erosion from lots under construction
Why are downstream floods generally caused by extended periods of rain in the drainage basin upstream of the flooded area?
Stream discharges tend to increase downstream. This means a large quantity of water is needed to cause a flood.
In situations where the removal of wetlands has increased flooding, the wetlands can be restored. In situations where overland flow is excessive, ______ are a possible method of flood mitigation.
artificial wetlands
A flood peak appears differently on a stream hydrograph at various points along the drainage. Match the hydrograph line to the point in the stream.
A matches Choice, Near mouth; most lag time Near mouth; most lag time B matches Choice, Midstream; some lag time Midstream; some lag time C matches Choice, Near headwaters; least lag time Near headwaters; least lag time
Identify the water process in the hydrologic cycle by matching the letter to the name.
A matches Choice, Transpiration Transpiration B matches Choice, Groundwater baseflow Groundwater baseflow C matches Choice, Infiltration Infiltration D matches Choice, Evaporation Evaporation E matches Choice, Precipitation Precipitation F matches Choice, Overland flow Overland flow
In arid climates, the water table is often the level of streams, which creates losing streams that feed groundwater. In humid climates, the water table is higher the stream, and groundwater to gaining streams.
Blank 1: below or under Blank 2: discharges
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.
Blank 1: channelization
A flood control measure meant to moderate stream flow and minimize flooding by partially blocking a stream is a(n)
Blank 1: dam or reservoir
Loss of navigable rivers for people and aquatic life and the intentional flooding of entire valleys are negative effects of which flood-control method?
Blank 1: dams, dam, or reservoir
The volume of water moving through a specific point in a stream channel over a certain amount of time is known as stream
Blank 1: discharge
We quantify flooding by measuring either the stage or the of the river.
Blank 1: discharge
Floods that most often occur in the lower portions of drainage basins are called
Blank 1: downstream
Floods that most often occur in the lower portions of drainage basins are called floods and often affect a wider floodplain than flash floods, which tend to occur upstream in the drainage basin.
Blank 1: downstream
When comparing upstream and downstream floods, floods cause greater property damage because they cover large areas for long periods of time, and floods most commonly pose the greatest risk to people because there is less time to evacuate.
Blank 1: downstream Blank 2: upstream
An area containing all tributaries and streams within a single network is called a(n) basin.
Blank 1: drainage
The red line in the image shows a , which determines the stream network that precipitation will flow into depending on where it falls.
Blank 1: drainage Blank 2: divide
Flooding events where streams rapidly overflow their banks are called floods.
Blank 1: flash or upstream
Driving through floodwater can be very dangerous. Just 2 feet of water can cause a vehicle to and be carried away or flipped over by the current.
Blank 1: float
Raising a house on a platform and building a personal levee are two common examples used by homeowners for protection
Blank 1: flood
The height of the water surface in a stream at any point is called the stage of the stream. A stream has flooded and has reached stage when the water has exceeded the height of the stream banks.
Blank 1: flood
Vegetation removal, building construction, and vast impermeable surfaces are elements of human impact that have led to increased of streams in a short period of time.
Blank 1: flooding
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
Blank 1: floodplain
The National Flood Insurance Program regulatory floodway consists of two zones; the first being the , where floodwaters are the deepest and fastest, and the flood , which borders the regulatory zone.
Blank 1: floodway Blank 2: fringe
he National Flood Insurance Program regulatory floodway consists of two zones; the first being the , where floodwaters are the deepest and fastest, and the flood , which borders the regulatory zone.
Blank 1: floodway Blank 2: fringe
The stream is measured as the steepness of the stream channel.
Blank 1: gradient, slope, or grade
A plot of discharge over time is a
Blank 1: hydrograph
The headwaters of a drainage system is in the upper portion where a stream begins. The of a stream is in the lower portion where a system empties into an ocean, lake, or other river.
Blank 1: mouth
Compared to streams, streams have been altered from a diverse ecosystem to an artificial environment with fast-moving waters, uniform depth, a smooth channel bottom, and smooth banks.
Blank 1: natural, native, or original Blank 2: channelized, straightened, or lined
The frequency that a flood of a certain discharge will repeat for a particular stream is known as its interval.
Blank 1: recurrence
Urbanization can increase peak discharge and shorten lag time of precipitation events, creating a higher potential for flash floods. Retention ponds can peak discharge and lag time, thereby decreasing the potential for flooding.
Blank 1: reduce, lessen, or decrease Blank 2: increase or lengthen
Large basins that trap some surface runoff and delay it from flowing directly into a stream are called ponds.
Blank 1: retention
People have historically chosen to live along because they provide a source of water for drinking and irrigation, a mode of transportation, and a source of food.
Blank 1: streams or rivers
This stream hydrograph compares the pattern of discharge for a landscape with natural vegetation cover and the same landscape after it has been urbanized. Line A demonstrates a landscape with higher peak discharge and flash flooding characteristics. Line B shows a landscape with lower peak flow and a longer lag time.
Blank 1: urbanized, city, urban, or developed Blank 2: natural or native
When is(are) removed from the landscape, greater amounts of overland flow carry more sediment into the stream channel. The additional sediment eventually deposits in the and reduces capacity. A capacity reduction increases flood severity.
Blank 1: vegetation, plants, or flora Blank 2: channel or stream
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.
Blank 1: velocity or speed
Reducing insect-borne diseases and increasing land suitable for development are reasons that have been drained.
Blank 1: wetlands, marshes, bogs, or swamps
Which of these are methods used by homeowners to protect homes in floodplains from flooding?
Building the home on an elevated platform Constructing a levee around the home
How might changes in regional climate be measured by streams?
Changes in flood recurrence intervals
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 these changes are observed with the removal of vegetation in a drainage basin?
Decreased infiltration Increased soil erosion Increased overland flow
Floodplains are the flat land that streams will fill with water when they overflow. How are floodplains formed?
Deposition of sediment during flooding Migration of meanders
Levees generally provide a false sense of security to those living near them because they can fail quite easily; this is the levee effect. Compare the type of development in floodplains controlled by levees versus that in uncontrolled floodplains by selecting the correct description.
Development in a floodplain with levees is often next to the levees, whereas in a floodplain without levees, development is outside the floodplain.
What is the name of a topographic high point in the landscape that determines the stream network that precipitation will flow in?
Drainage divide
What effect does the widespread removal of wetlands have on flooding?
Flooding increases.
What is a common level of flood risk assumed by homeowners?
Flooding once between 50 and 100 years.
Match the government regulation definition and the natural definition of floodplains.
Government regulation matches Choice, Land susceptible to flooding Land susceptible to flooding Natural matches Choice, Flat areas adjacent to streams Flat areas adjacent to streams
Along with urbanization, how have human actions exacerbated flooding risk in Houston?
Groundwater and oil pumping have created a bowl-shaped depression underlying the city that tends to collect water.
Where is the mouth of a stream located?
In the lower portion of the drainage system where the stream empties into a lake, ocean, or another river
What are the main goals of channelization?
Increase the volume of the channel Increase the velocity of water flow
What is the common cause of downstream floods?
Rain falls over large areas of the upper drainage basin for days or weeks
Which of these characteristics can determine the risk of flooding for a stream?
Rainfall intensity Rainfall duration
How does vegetation help mitigate flood hazards?
Reduces water velocity Increases soil infiltration Absorbs water
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.
How are retention ponds positioned so they can counter the effects of urbanization on storm water runoff?
Retention ponds are placed adjacent to areas with large amounts of impermeable surfaces.
In the 1900s, engineers drained the swamps of New Orleans in order to develop those areas but in doing so ______
the land subsided and created a bowl-like depression
This plot of discharge over time is a ______.
hydrograph
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
What climates are associated with gaining and losing streams? Match each climate to its stream type.
Arid climate matches Choice, Losing streams Losing streams Humid climate matches Choice, Gaining streams Gaining streams
Which type of flood management structure is shown here?
Artificial levee
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
Which of these can be a base level for a stream?
Ocean Lake Larger stream
