Lecture 8 flashcards
(25 cards)
____ ___: an area that drains all precipitation received as a runoff or base flow (groundwater sources) into a particular river/set of rivers
drainage basin
what drainage pattern is tree-like?
dendritic
what separates one drainage basin from another?
a divide - a topographic high point
when does a flood occur?
when stream discharge > channel capacity (causes water to overflow its banks)
what is a recurrence interval?
an estimate of how often a flood of a given size is likely to occur (e.g. a 100-year flood)
what factors affect flood recurrence estimates?
CC, U, D
climactic cycles (drought/excessive rain),
urbanization
damming
what causes regional floods?
melting snow, heavy rain, frozen ground, saturated soils, or slow-moving storm systems (e.g. Calgary 2013 flood)
what causes flash floods?
intense rainfall, steep topography, impervious surfaces (urban areas), and poor infiltration
what is an ice-jam flood?
when ice floes block a river, forming a temporary dam. when it breaks, it causes a sudden flood downstream
what is a dam-failure flood?
a catastrophic flood resulting from the sudden release of water due to the collapse of a dam or levee
what is an artificial levee and what’s a downside of it?
a manmade mound along a river to increase channel capacity. downside: sediment builds up, raising riverbed and increasing flood risk over time
what’s the main goal of flood-control dams?
to store floodwater and release it slowly, reducing the flood crest
what are t here major flood control structures?
Artificial levees,
flood-control dams,
channelization
what is channelization?
modifying a stream to increase flow speed - often by straightening or deepening the channel
what’s a non-structural approach to flood management?
floodplain management - identifying high-risk areas and regulating land use to minimize damage
What is the main cause of a flash flood in urban areas?
A) The presence of numerous dams and reservoirs
B) Heavy rainfall over many days
C) High proportion of impervious surfaces like pavement
D) Failure of natural levees
C
Which of the following correctly compares a 25-year flood to a 100-year flood?
A) A 25-year flood is less severe and 4x less likely
B) A 100-year flood is 4x more frequent than a 25-year flood
C) A 100-year flood is larger and less likely to occur than a 25-year flood
D) A 25-year flood only happens once every 25 years exactly
C
Which flood control method is most likely to lead to a buildup of sediment in the river channel, potentially increasing future flood risk?
A) Channelization
B) Artificial levees
C) Floodplain zoning
D) Constructed wetlands
B
What is one major drawback of flood-control dams over time?
A) They increase the melting of snowpacks
B) They cannot store any groundwater
C) Sediment buildup reduces reservoir capacity
D) They are only useful during winter floods
C
An ice-jam flood is most likely to occur when:
A) A dam is overtopped during a hurricane
B) Meltwater penetrates the permafrost layer
C) Rising stream levels break up river ice into floating blocks
D) Flood-control dams are drained too quickly
C
Channelization increases the speed of water flow. What is a potential side effect of this?
A) Floods become impossible
B) River erosion decreases significantly
C) Sediment transport is reduced
D) Downstream erosion and flooding may increase
D
Which event is an example of a dam-failure flood?
A) Sea-to-Sky Highway flooding due to rainfall
B) Hurricane Katrina overtopping New Orleans levees
C) Derna, Libya collapse of twin dams in 2023
D) Brantford’s ice-jam flood
C
Which best describes a false sense of security related to structural flood controls?
A) Dams always fail during flash floods
B) People believe they’re fully protected and develop floodplains
C) Non-structural approaches are never used
D) Artificial levees are 100% reliable
B
Which factor does NOT affect the accuracy of flood recurrence estimates?
A) Number of years of stream gauge data
B) Urban development in the drainage basin
C) Drought or excess rainfall cycles
D) Composition of the riverbed sediment
D
