EV1005 - L7-8 Streams and Floods Flashcards
How many times more water falls on the oceans than it does on the land?
4x more water falls in the ocean than on the land
The water cycles consists of inputs (1), migration (2) and outputs (3). What are these?
Inputs - precipitation (rain, snow, hail, etc)
Migration - run-off off the land and from rivers, infiltration into ground water
Outputs - transpiration, evaporation and discharge of ground water to ocean or surface
how much water that evaporates over oceans returns to the ocean? (%)
90% of the water that evaporates from the ocean returns to the ocean. 10% falls over the land
What are the water reservoirs? (6)
Atmosphere Oceans bodies of water on land (lakes, rivers etc) Glaciers Snowfields Groundwater
True or False
Residency times vary greatly in different reservoirs.
True
Residency time can vary from days to millions of years
Order these reservoirs in order of shortest to longest residency time
Lakes Soil moisture Rivers Glaciers Oceans Seasonal snow cover Atmosphere Groundwater - Shallow Groundwater - Deep
Atmosphere - 9 Days Soil moisture - 0.2 years Seasonal snow cover -0.4 years Rivers - 0.4 years Glaciers - 40 years Lakes - 100 years Groundwater (Shallow) - 200 years Oceans - 3,200 years Groundwater (Deep) - 10,000 years
Define Transpiration
Process by which water that is absorbed by plants, usually through the roots, is evaporated into the atmosphere from the plant surface, such as leaf pores. One of the ways water travels between reservoirs.
Define condensation
Condensation is the process of water vapor returning to its liquid state as temperatures cool. Clouds form when water condenses in the atmosphere. One of the ways water travels between reservoirs.
Define precipitation
Rain, snow, sleet, or hail that falls to the ground (or ocean). One of the ways water travels between reservoirs.
Define runoff
The draining away of water (or substances carried in it) from the surface of an area of land, a building or structure, etc. One of the ways water travels between reservoirs.
Define infiltration
Infiltration is the process by which water on the ground surface enters the soil. One of the ways water travels between reservoirs.
Define Melting
The runoff produced by melting snow or ice. One of the ways water travels between reservoirs.
Define groundwater flow
The movement of groundwater between infiltration and discharge into streams, lakes or oceans (or man-made pumps). One of the ways water travels between reservoirs.
What areas exhibit the most about of runoff?
A) Polar
B) Temperate areas
C) Tropical areas
C)
Tropical areas generally have the highest amount of runoff.
Order these names for the collection of runoff
Rill
Tributary
Sheetwash
Trunk Stream
Sheetwash becomes rills which flow into tributaries. tributaries are connected to the main trunk stream; the body of water that flows directly to the ocean.
Sheetwash - Rill - Tributary - Trunk Stream
What is a perennial stream?
Streams that run all year long because the water table is always intecepted
What is an ephemeral stream?
A stream that dies up for periods during the year. water collected in channel is lost to underground flow and the stream only flows when the ground level intercepts the water table
Define wetted perimeter
The perimetre of the ground the water is touching
Define thalweg
The deepest part of a water channel
Which has a rougher base? Upstream or downstream channels?
Upstream channels are usually rougher and have more turbulence.
Why are clays harder to erode? (2)
They have ionic bonds holding them together
they are platy materials and form smooth surfaces with little friction
What size particle is the easiest to move?
A) Clay
B) Silt
C) Sand
D) Gravel
C) Sand
Sand moves in normal river flow. Clay and silt don’t have a large enough surface area and clays also form ionic bonds that hold them together. Gravels are often too heavy to be transported easily.
Define Saltation
Intermittent ‘jumping” of grains that are lifted by turbulence into a flow of water
How does velocity assist in moving boulders underwater?
Velocity of water passing over a boulder is greater than that passing under the boulder (because the boulder is sitting on the bottom of the stream and further away from the thalweg) therefore boulders roll downstream
Explain the capacity of a stream
The maximum load of sediment a stream can carry
Explain the competence of a stream
The largest particle that a stream can transport
True or False
Erosion happens when Capacity < Load.
False
Erosion happens wen Capacity is greater than load
True or False
Deposition happens when Capacity < Load
True
When the load is greater than the capacity, deposition occurs
Marshlands have
A) Low capacity and low competence
B) High capacity and low competence
C) Low capacity and high competence
D) High capacity and high competence
A) Low capacity and low competence
Trunk streams have
A) Low capacity and low competence
B) High capacity and low competence
C) Low capacity and high competence
D) High capacity and high competence
B) High capacity and low competence
Highland streams have
A) Low capacity and low competence
B) High capacity and low competence
C) Low capacity and high competence
D) High capacity and high competence
C) Low capacity and high competence
Flooded rivers have
A) Low capacity and low competence
B) High capacity and low competence
C) Low capacity and high competence
D) High capacity and high competence
D) High capacity and high competence
True or False
Discharge increases as you go downstream
True
Discharge increases as you go down stream
True or False
Channel smoothness decreases as you go downstream
False
Smotheness increases as sediments are diposited
True or False
The gradient/slope increases as you go downstream
False
The gradient decreases and becomes flatter as you go downstream
True or False
More resistant bedrock along water ways is associated with steep valleys
True
What are alluvial fans?
How are they created?
Where water leaves a mountain valley and enters a relatively flat plain. the decrease in velocity lowers the streams capacity and competence. deposition causes sediments to settle creating large ‘fans’
What are braided streams?
How are the formed?
Consist of interlacing channels of water formed after rapid fluctuations in velocity. When velocity drops large amounts of sediment are deposited. Water still flowing through the area erodes small streams through the sediment. (often caused by glacial outwash)
What is alluvium?
River deposits
What is an oxbow lake?
When the meanders of a stream are exaggerated to the extent that it doubles back on itself and cuts through. Sediment is deposited along the edges and a lake is created separate to the stream. (eg Australian Billabongs)
What are point bars?
Where the stream deposits sediments/alluvium. Occur only on the inside bends of meandering streams
The Nile delta is is
A) Wave dominated
B) River dominated
C) Tide dominated
A) Wwave dominated
The Mississippi River delta is
A) Wave dominated
B) River dominated
C) Tide dominated
B) River dominated
The Ganges River delta is
A) Wave dominated
B) River dominated
C) Tide dominated
C) Tide dominated
The Barron River delta is
A) Wave dominated
B) River dominated
C) Tide dominated
A) Wave dominated
Why do flash floods occur in urban areas?
Because of low infiltration and high runoff levels
True or False?
Riverine floods happen suddenly and with little notice
False
They come with many hours, days or weeks notice and last for extended periods of time.
Which flood results in the highest amounts of deposition?
A) Flash floods
B) Riverine floods
B) Riverine floods
These floods spill over onto the floodplains and therefore velocity and capacity drop
Why are flood plains popular places for housing or farming land? (2)
1) In flood, sediments and nutrients are deposited on flood plains making the soil fertile for crops
2) the land is flat and good for farming machinery and easy to build houses on
What is a problem with man made levees?
They may only offer protection for a limited region and cause greater flooding in other areas
