Flooding - Human Activity and Flooding Flashcards
what type of human activities has increased the frequency and severity of flooding?
clearing of land for agriculture, building of cities, and construction of transportation networks
t or f: some measures to reduce flooding in one area have led to increased flooding in other areas
t
land-use factors that affect flooding
- removal of natural vegetation
- destruction of wetlands
- construction activity
- urbanization
what are the consequences of widespread removal of forests and grasslands?
- less infiltration capacity resulting to more overland flow and increases the ability of water to move downslope
- increased overland flow and erosion thereby resulting in sediment pollution
excessive dislodged sediment is moved off the
landscape into drainage systems which causes
channels to become filled with sediment
sediment pollution
how does sediment pollution affect flooding?
reducing the capacity of streams to carry water thereby increasing the frequency and severity of flooding
this refers to the level of suspended sediments
turbidity
why are wetlands important in reducing flooding?
wetlands are natural flood-retention basin, they accumulate floodwater
land consisting of marshes or swamps; saturated land
wetlands
wetlands are commonly found in ____________ and ____________ in which case they are called ___________
topographic depressions ; adjacent to river channels ; riparian wetlands
how does destruction of wetland affect flooding?
reducing the landscape’s ability to store water
are lands that occur along the edges of rivers, streams, lakes, and other water bodies
riparian zones
in many parts of the world, wetlands have been viewed as __________
wastelands
t or f: wetlands are generally porous
t
large pipes called _____ are typically sued for small streams that flow intermittently
culvert
what is the downside of using a culvert?
the amount of discharge able to flow through the culvert is limited to its diameter and is unable to handle large volume of water, thereby causing upstream areas to become flooded
most construction activities involves _______thereby, increasing chances of flooding
removal of natural vegetation
The process of removing silt from a body of water (e.g., sand and gravel extraction)
desiltation
urban areas in developed countries typically have significant portions of the land covered with __________ such as concrete and asphalt, causing less infiltration capacity
impermeable surfaces
t or f: urbanization leads to shorter lag times between precipitation events and peak discharge
t
t or f: it takes far less time for overland flow to reach a stream channel than water infiltration and movement through the groundwater system
t
what are the consequence of urbanization?
- more frequent flooding
- higher flood crests
- shorter lag time between rainfall and peak discharge
what are the flood mitigation measures?
- dams
- artificial leeves
- channelization
- retention basins
- erosion control
- flood proofing
- floodplain management/zoning
- education
this serves as a protection against floods and as an important source of freshwater and electrical power
dams
what is the downside of a dam?
heavy or prolonged rains can sometimes cause the reservoir to reach its maximum level, thereby engineers are forced to release water at such high rate causing flooding on the downstream areas
t or f: structural failure of a dam can generate a truly catastrophic flood
t
built by humans to keep a river from overflowing its banks
artificial leeves
large concrete panels used to build artificial leeves
floodwalls
any low ridge or earthen embankment built along the edges of a stream or river channel to prevent flooding of the adjacent land.
earthen leeve
what is a the downside of artificial leeves?
they disrupt natural drainage system by disconnecting a river from its floodplain
will hold far less water than what the floodplain is capable, thus, will act as bottlenecks restricting the flow of a river
t or f: artificial leeves act as bottlenecks that make flood worse in upstream areas
t
involves straightening and deepening of a stream channel
channelization
channelization increases a streams _________
discharge capacity
channelization results in an increase in ________ and _______
stream gradient and water velocity
what is the most serious consequences of channelization?
- flooding downstream becomes worse because in non channelized sections, discharge capacity remains the same
- increased water velocity causes stream to erode downward, leaving steeper banks that are prone to mass wasting
temporarily stores some the excess water in a series of depressions which are constructed within a tributary network
retention basins
involves practices that tend to keep soil particles in place so as to minimize the amount of material able to move downslope
erosion controls
are a type of barrier in which
vegetated strips line the banks of stream channels,
trapping sediment before it can enter the drainage
network
stream buffers
are made of a synthetic
fabric that is fine enough to trap sediment, but yet allows some water to pass
silt fences
ponds constructed for the purpose of
trapping any sediment that makes its way into a
drainage system
silt basins
types of erosion controls
stream buffers, silt fences, silt basins
fabrics used in geotechnical applications, such as road and railway embankments, earth dikes, and coastal protection structures, designed to perform one or more basic functions such as filtration, drainage, separation of soil layers, reinforcement, or stabilisation
geotextiles
Involves raising the building above the expected flood level
flood proofing
For those who do not plan ahead, there is always the possibility of constructing an emergency levee using
sandbags
involves providing federally subsidized flood insurance to property owners
Flood Plain Management
how is a flood map for flood plain management generated?
By comparing the elevation of the land surface to the projected flood height of a 100-yr flood
flood plain management is sometimes called
floodplain zoning
involves identifying areas adjacent to a stream that will be inundated in a 100 year flood.
floodplain zoning
regulatory floodplain is divided into the ________
and ___________, and regulations then restrict the type of development allowed in each of these two zones.
flood fringe ; floodway
a very cost effective means
of reducing the number of fatalities and property
damage.
public education
Approximately half of all flash flood fatalities are ______
vehicle-related
flood susceptibility is divided into how many classes?
4 classes
very high
high
moderate
low
