flooding processes Flashcards
what causes flooding? (7)
natural processes starts on land flood hazard construction in flood hazard areas drainage of the land poorly designed urban areas flood defences infrastructure failure.
what causes the earth largest floods in descending order?
proglacial-lake overflow landslide dam failure lake-basin overflow subglacial volcanic eruption caldera-lake break ice-jam and snowmelt rainfall
where do the largest rainfall floods occur?
where there are world’s largest basins, but tropical basins generate more water due to the monsoon climate region causing the largest mass of water to be dropped at a certain time.
what is the probable maximum flood?
the largest flood that could physically occur at the location of interest. it is a very rare event and defines the extent of flood-prone land in a floodplain.
what is the likelihood of the probable maximum flood?
1 in 10,000 and 1 in 10,000,000 years.
what are the types of floods? (5)
winter rainfall floods summer convectional storm-induced floods snowmelt floods sewer flooding/urban drainage flooding urban basement flooding
what is a flood?
exceed of water.
how do you distinguish what type of flood it is?
distinguished either by the event which caused the water or by the process by which it creates a problem
what controls peak magnitude?
the volume of water, the proportion of rain that generates quick flow. rainfall intensity and the amount of saturation, catchment geology and time.
what controls time to peak?
the size, shape, drainage density, and slope. these are all catchment physical properties.
what controls the rate of recession?
depends on the catchment geology.
what is exceedance probability?
is the probability that an event greater than or equal to X occurs in any one sample interval;.
what is a return period?
the average time between sample intervals containing an event greater than or equal to X.
why do flood frequency curves vary?
for a given catchment type: variation in floods depends on variation in flood-producing rainfall.
for a given climate: variation in floods depends on catchment physical properties and geology.
what are flood hazard characteristics? (10)
the magnitude of the flood rate of floodwater rise duration of flooding depth and velocity of flowing waterevacuation problems effective flood access size of population at risk land use flood awareness and readiness effective flood warning time.
