GLG-112 Exam 3
"U" shape valley
U-shaped valley or glacial trough is formed by the process of glaciation. It has a characteristic U shape, with steep, straight sides and a flat bottom. Glaciated valleys are formed when a glacier travels across and down a slope, carving the valley by the action of scouring. When the ice recedes or thaws, the valley remains, often littered with small boulders that were transported within the ice. -Low-medium sinuosity in "U" shaped valleys
Sinuosity (low vs high)
a continuously derivable curve having at least one inflection point is the ratio of the curvilinear length (along the curve) and the distance (straight line) between the end points of the curve. This dimensionless quantity is obtained by the following report: actual path length/shortest path length
Hydrograph
a graph showing changes in stream discharge, water depth, or stage over time
This is created when two cut banks migrate towards one another and then merge
abandoned meander
The weight of a column of air bearing down on the surface of the Earth per unit area
barometric pressure
This controls wind speed and the height of worm surge in a cyclone
barometric pressure
The location within the drainage basin where discharge per unit area will be the lowest
base level
The lowest elevation to which a stream will erode
base level
Braided Stream
braided patterns have numerous sand and gravel bars and islands that divide and reunite the main channel, especially during low flow. Overall, braided channels tend to be wide and shallow, compared to meandering channels. -Many channels that change course often and "braid" with one another
The stream type that develops when water velocity quickly slows down (dominated by deposition)
braided stream (large amount of sediment and little water)
The surface area within which all enters on stream system
catchment area
Retention pond
comparison of runoff from a paved area, which goes directly through a worm drain to a steam, with runoff that is stored temporarily in a retention pond before draining to a tram.
Know how to identify a cut bank and point bar in a stream.
cut bank: the outside of a bend point bar: inside of a bend
How do meandering streams move their channels (i.e. through creation of cut banks and point bars)?
cut bank= erosion point bar= deposition
State whether the following properties of a stream increase or decrease as water moves from the headwaters to base level. Why?--Maximum grain size
decrease! -he size of particles that make up the bed load of the stream tends to decrease. Even though the velocity of the stream increases downstream, the bed load particle size decreases mainly because the larger particles are left in the bed load at higher elevations and abrasion of particles tends to reduce their size.
State whether the following properties of a stream increase or decrease as water moves from the headwaters to base level. Why?--total sediment load
decrease...
What could cause the discharge of a 100-year flood to systematically decrease or increase over a period of decades?
decrease: urban planning increase: urbanization near stream
One negative effect of building levees along a river
decreased sediment supply to floodplain/levee "arms race"/false sense of security
A sedimentary feature created by sediment deposition at the mouth of a stream
delta (composed of sand deposition at the end of a rive)
An increase in water velocity and channel size will cause an increase in this
discharge (volume of water per time)
What properties of a stream will increase downstream of levees, if the stream is leveed on both sides?
discharge,water velocity
One stream property that increases downstream of levees
discharge/water velocity/ erosion
Describe the effect on erosion, water velocity, and discharge when you levee both sides of a stream.
downstream of levee= -increase discharge -increase water velocity -increase erosion in channel
The size of this area will determine how much water enters a stream
drainage basin/watershed/catchment area
One location on Earth where cyclones will not form
equator/north or south of 20 degrees latitude
A straight stream is dominated by this sedimentary process
erosion
This process occurs when water velocity speeds up
erosion
Base level
essentially the lowest elevation to which it may erode. Most often, this elevation is at or close to sea level, although a river may have a temporary base level such as a lake.
Storm surge will be the highest under this portion of a hurricane
eye (where the pressure is the lowest)
Heavy rain over small watershed will create this type of flood
flash flood
Flood discharge increases towards base level but this property of a flood will decrease
flood height (larger volume of water spread out over a wider area)
This location is deprived of sediment when levees are built
floodplain
Total sediment load
generally subdivided into bed load, suspended load, and dissolved load, based on how the river carries the material. -bed load: sand and gravel particles that slide, roll, and bounce along the channel bottom in rapidly moving water. Makes up less than 10% of total load. -
what is the primary control on the size of sediment a river can carry (max. grain size)?
gradient -rivers can carry larger grain sizes (cobbles,boulders) with the help of gravity on a steep slope
This is one of the only properties of a stream system that decreases as water moves from headwaters to base level
gradient (the slope of the land)
The location within a stream system that is referred to as the "zone of erosion"
headwater
Grain size is largest in this region of a stream
headwaters (mountains)
The stream type that is dominated by erosion and deposition
high-sinuosity meandering stream
This records stream discharge over time
hydrograph
State whether the following properties of a stream increase or decrease as water moves from the headwaters to base level. Why?--Channel size
increase! -as the amount of water increases towards the base level, the stream has to adjust. As discharge increases, generally width, depth, and velocity of the stream also increase.
State whether the following properties of a stream increase or decrease as water moves from the headwaters to base level. Why?--Velocity
increase! -stream will have the fastest velocity near base level because that is where the stream has the most water.
State whether the following properties of a stream increase or decrease as water moves from the headwaters to base level. Why?--Discharge
increase! -the deepest part of channel occurs where the stream velocity is the highest. Both width and depth increase downstream because discharge increases downstream. As discharge increases the cross sectional shape will change, with the stream becoming deeper and wider.
Which of the following is NOT typically a result of urbanization?
increased infiltration/absorption
The word that describes how water soaks into the ground
infiltration
after a landscape is urbanized_____will decrease because of pavement/parking lots/building ect
infiltration
How can we use recurrence intervals to project the 100-year flood for a river?
interval: the probability that a specific size flood will occur on a specific stream in any given year
What streams are dominated by: Erosion and Deposition
meandering
This type of stream where you would expect a regional flood
meandering stream
Hurricanes spin in a counterclockwise direction. As a result, the wind in this quadrant of the worm will be most damaging
northeast quadrant
The position on a steam meander that experiences deposition
point bar (inside of bend)
Choose the possible cause for the average 100-year flood discharge decreasing over several decades
rainwater harvesting
This term is usually used to describe flood frequency
recurrence interval (probability of a specific size flood per year)
Flash versus regional floods - how do they differ in peak discharge times, location, and causes? (maybe best to make a chart here?)
regional floods: Wide valleys, near local or regional base level Water discharge may peak over days flash floods:
A flood control method that captures surface water and delays its entrance into a stream
retention ponds
Sets of abandoned meanders on the flood plain
scrolls
A word that describes how a stream bends
sinuosity
Urbanization causes an increase on this in the communities
sirface runoff
One control on how fast a flood will rise and fall
size of the drainage basin. soil saturation levels. amount of rain/hour.
The speed of a flood crest during a regional flood
slow
Point bar
slower water on the inside of a meander bend deposits sand and sometimes gravel
A low-sinousity stream
straight stream (sinuosity describes the degree of bend in a river)
What streams are dominated by: Erosion
straight streams
Channelization
straightening, deepening, widening, clearing, and/or lining existing stream channels
Numbers assigned to streams in a system that describe how big those streams are
stream order
Lowering the elevation of a floodplain due to decreased sediment supply
subsidence
The name for water that drains off of the landscape
surface runoff
Recurrence Interval
the average time between flood events that are of equal or greater magnitude
Urbanization
the development of a natural landscape (roads, parking lots, ect.) -Decrease of infiltration -Increase of surface runoff
Floodplain
the flat surface adjacent to the river channel that is periodically inundated by floodwater, is, in fact, produced by the process of flooding.
Choose the best statement that describes how flooding is caused by storm surge
the ocean rises up under the low pressure system, causing the hurricane to bring water on shore with it as it moves
gradient
the slope of the land over which a river flows. This slope is determined by calculating the vertical drop in elevation of the channel over some horizontal distance.
Lag time
the time between the storm and onset of the flood -lag time decrease -discharge increase
Discharge
the volume of water moving through a cross section of a river per unit time. Calculated by multiplying the velocity of the flow (V) times the cross-sectional area (A) of the water in the channel.
discharge
the volume of water moving through a cross section of a river per unit time. Calculated by multiplying the velocity of the flow (V) times the cross-sectional area (A) of the water in the channel.
All wind in the northern hemisphere is deflected in this direction
to the right (as a result of the Coriolis Effect)
Trunk Stream
transporting system (trunk) -- the main trunk stream, which functions as a channelway through which water and sediment move from the collecting area toward the ocean. (Erosion and deposition also occur in a river's transporting system)
The name of the highest order stream in a system
trunk stream
Flash flood
typically occur in the upper part of a drainage basin and in some small drainage basins of tributaries to a larger river. -Small discharge, high flood level (actual height of the water) -Flash floods occur in narrow valleys ("V" and "U"). The volume of water is relatively small but the height is significant.
This happens to stream valleys as water moves through the drainage basin towards base level
valleys get wider as the streams get bigger towards base level
How does the presence of levees decrease sediment supply to the floodplain?
water is unable to get out and deposit sediment onto floodplains
Even though the land is flatter this property of stream actually increases toward base level
water velocity
What is the primary control on whether a stream erodes or deposits sediment?
water velocity -when water speeds up, sediment is eroded. -when water slows down, sediment is deposited
Channel width is highest in this type of valley
wide valley
Gradient is highest in this type of stream valley
"V" shaped valley (classiest to the headwaters)
What are the negative effects of building levees on two sides of a stream?
"arms race" -decrease sediment supply on floodplains -no water to crops
Explain stream order. Know how to figure out the order of a stream given a stream diagram
-1st order streams have no tributaries. 1st orders join to form 2nd orders and so on.. -A dendritic stream pattern is made up of a series of tributaries with on main trunk -the higher the order, the bigger the stream, the more water it holds
Three zones define a stream system
-Zone of erosion in headwaters (steep gradient) -Zone of transportation is central -Zone of deposition towards mouth of water (shallow gradient)
How does urbanization increase the risk of flooding (include an explanation on surface runoff and lag time)?
-decrease in infiltration (water does not soak in to asphalt/concrete) -lag time decreases between center of mass of rainfall and center of mass of runoff *lag time:the time between the storm and onset of flood -lag time decrease/discharge increase -more surface runoff=bigger flood in shorter time
How do retention ponds decrease discharge of a flood?
-help reduce runoff -capture surface runoff and allow water to soak into ground (usually built next to parking lots) -increase infiltration -decrease surface runoff that enters stream
What is a flood recurrence interval?
-interval is the probability that a specific size flood will occur on a specific stream in any given year
What is the relationship between discharge and channel size?
-meandering streams have the largest discharge and channel size
(Pakistan and Georgia/South Carolina hydrograph exercises from class)
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(in class exercise- How do river systems change downstream)
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A large storm system hovers over central Illinois for 4 days, dropping 4 in of rain over much of the state. What type of flood would be created downstream? What would the hydrograph look like?
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A levee breaks in the middle of a massive, regional storm. What would the hydrograph look like just downstream?
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A storm drops 5 in of rain in a narrow canyon, what would the hydrograph look like?
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Flood frequency
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How are erosion, deposition, and water velocity affected?
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Hydrograph scenarios (draw hydrograph's?)
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Know how to identify abandoned meanders, scrolls, and oxbow lakes
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Peak annual flood
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Understand how to read, plot, and interpret a hydrograph
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What is done to a stream when it is channelized?
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What property of a hurricane will decrease as the hurricane gains strength (increase in category)?
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Where is barometric pressure the lowest?
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maximum grain size
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How does a braided stream form?
...-Many channels that change course often and "braid" with one another
Wide Valley
...a wide valley -High sinuosity in wide valleys
Straight stream
...straight stream occur in in "V" shaped valleys ...straight streams may become braided in "U" shaped valleys ...develop on the steepest gradient?
Why do stream valleys get wider toward base level?
...water amount increases causing stream to adjust in size. ...velocity increases causing erosion ...delta
Which flood would have the highest discharge?
100-year flood *the lower the probability = higher discharge
which of the following locations should have the steepest gradient?
2nd order -gradient is steepest closest to the headwaters
Hurricanes can only form between what latitudes north and south of the equator?
5º and 20º
"100-year" flood
= 1/100 or 1% *lower the probability = higher discharge/ smaller the number = bigger the flood
Mouth
A river mouth or stream mouth is the part of a river that flows into a river, lake, reservoir or ocean.
velocity
A stream's velocity depends on position in the stream channel, irregularities in the stream channel caused by resistant rock, and stream gradient. The average velocity is the time it takes a given particle of water to traverse a given distance.
"V" shape valley
An elongated lowland between ranges of mountains, hills, or other uplands, often having a river or stream running along the bottom. An extensive area of land drained or irrigated by a river system.
What streams are dominated by: Deposition
Braided streams dominated by sediment deposition -Stream rushes out of the mountains and drops its sediment load on the plains at the base
The name for the stream pattern that resembles the shape of an oak tree
Dendritic stream pattern (smallest streams at the top, largest at the bottom)
in the North Atlantic Ocean, the Coriolis Effect (effect of earth's spin on weather patterns) causes hurricanes to travel along a curved path in what general direction?
East to West
Hydrographs (Flood Crest Movement graphs) - how can you tell the difference between a flash flood and a regional flood just by looking at the graph?
Flash food: A curve that rises and falls quickly with the x-axis units in hours.
Choose the statement that best describes how flood crests move through a watershed from headwaters to base level.
Floods crest quickly in the headwaters region and get slower toward base level
How can hydrographs show the movement of a flood through the stream system from the headwaters to base level (i.e. flood crest movement)?
Floods crest quickly in the headwaters region and get slower toward base level
Explain why the total sediment load may decrease quickly at the mouth of a river and form a delta.
If the gradient of the stream suddenly changes by emptying into a flat-floored basin, an ocean basin, or a lake, the velocity of the stream will suddenly decrease resulting in deposition of sediment that can no longer be transported. This can result in deposition of such features as alluvial fans and deltas.
Flood crest
In the case of river flooding, it is the highest stage or level of a flood wave as it passes a particular point. Gauges along the river record the level of the water, and the highest level recorded at each gauge will be the crest for that gauge.
Low pressure systems create this type of weather
Inclement (bad) weather/storms
Meandering Stream
Meandering, similar to the curves of a moving snake. Meanders migrate back and forth across the floodplain over a period of years to decades. Water moves faster along the outside of the meander bend during low to relatively high flows. The fast moving water erodes the riverbank on the outside of the bend to form a steep or near-verticle slope known as a *cutbank. *largest channel size -Meandering streams occur in "U" shaped and wide valleys -highest order stream
stream order
Second order streams only have first-order streams as tributaries. Third order streams only have second and first order streams as tributaries, etc. As the order of the stream increases, the discharge increases, the gradient decreases, the velocity increases, and the channel dimensions (width and depth) increase to accommodate the increased discharge.
What would you expect a flash (rapid) flood to look like?
Small discharge, high flood level (actual height of the water) -Flash floods occur in narrow valleys ("V" and "U"). The volume of water is relatively small but the height is significant.
Delta
Stream flow expands and slows down as a river goes from mountains onto plains or from a channel into an ocean, lake, or pond. At these points the river commonly forms a triangular or irregular shaped deposit known as a delta if it extends into a ledger body of water
Cut bank
The fast-moving water erodes the riverbank on the outside of the bend to form a steep or near-vertical slope
Peak discharge
The highest flow in the channel is known as the peak discharge.
channel size
The stream channel is the conduit for water being carried by the stream. The stream can continually adjust its channel shape and path as the amount of water passing through the channel changes.
This type of flood reaches its peak discharge over several days
Regional flood
One way to decrease the peak discharge for flooding in urban areas
Rainwater harvesting. building retention ponds. increasing infiltration through vegetation. rainwater harvesting.