Floods

Question 1

Threshold Exceedence

Answer 1

a peak discharge that exceeds a given threshold

Question 2

Annual maximum flood

Answer 2

the highest discharge in any one year

Question 3

Mean annual flood

Answer 3

an index of cental tendency of the distribution of flood magnitudes. often estimated by averaging the series of annual maximum floods

Question 4

T-year return period flood

Answer 4

an index based on the upper tail of the distribution of flood magnitudes

Question 5

Data problems

Answer 5

floods are hard to measure in the field, rarity mean few opportunities to calibrate

Question 6

average frequencies

Answer 6

need long records to define even moderate return periods

Question 7

interpretation problems

Answer 7

tendency to equate return period with a forecast by an event mat occur in less time or may not even occur

Question 8

Multi0decadal variability

Answer 8

clustering of relatively flood-rich and flood poor epochs

Question 9

Non-stationarity

Answer 9

• catchment changed imply differing consequences through time
• past may not be representative of the future

Question 10

Impact of urbanisation on floods

Answer 10

• increases flood frequency, more floods
• accelerates due to improved drainage, earlier peak flow
• magnifies due to more impermeable surfaces, higher peak flow
• reduces sensitivity to antecedent conditions

Question 11

approaches to mitigate floods

Answer 11

• permeable pavement
• water filled tube
• restoration of original meanders and floodplain from straightened rivers
• demountable wall