Lecture 17: Floods

Question 1

evaporation and precipitation

Answer 1

• condensation and precipitation
• part of the hydrologic cycle

Question 2

runoff and infiltration

Answer 2

• what paths does water take after precipiation on land
• runoff = a portion flows across the surface into streams
• infiltration = portion of precipitation that soaks into the ground

Question 3

transpiration

Answer 3

• water that is absorbed by plant roots
• leaves release water vapor through transpiration

Question 4

volcanism

Answer 4

• at subduction zone the water is brought to the center of the earth and causes volcanism

Question 5

drainage basin

Answer 5

• area of land that convey all runoff into a particular body of water
• acts as a funnel evaculating water to a single outlet

Question 6

basin drainage density

Answer 6

• measure of the tendency of a drainage basin to flooding
• drainage density = (length of all stream segments)/(area of basin)
• low drainage density = water runs off over long distances before reaching streams
• high drainage density = water channel quickly moves into stream and is transmitted to main channel

Question 7

discharge

Answer 7

• volume of water flowing in a stream channel per unit of time
• Q=AxV
• Q = discharge
• A = cross sectional area (m^2)
• V: flow velocity (m/s)

Question 8

load

Answer 8

sediments transported by a stream
- fine sediments are suspended or dissolved
heavy material hop on the stream bed

Question 9

channel gradient

Answer 9

• slop = delta elevation/delta distance
• higher gradient at the head
• lower gradient at the mouth

Question 10

stream path sinuosity

Answer 10

• typical path of a meandering stream
• the more curves in the river the more sinuosity it has

Question 11

mechanisms decreasing flow velocity

Answer 11

• downcutting to decrease gradient
• increasing sinuosity
• increasing amount of load

Question 12

hydrometeorological floods

Answer 12

• abundant rains
• spring melt
• april and may are vulnerable

Question 13

snowmelt - runoff floods

Answer 13

• when the amount of meltwater runoff exceeds the capacity of streams to contain the flow
• saturated soil
• can be days and weeks

Question 14

storm rainfall floods

Answer 14

• torrential rains accompanied by storm surges moving inland and high tides
• develop rapidly (flash floods) hours or days

Question 15

rain on snow floods

Answer 15

• combination of snowmelt runoff and storm rainfall floods
• rain is augmented by melt water to generate substantial runoff

Question 16

ice jam floods

Answer 16

• temporary obstruction of river flow by ice buildup

Question 17

natural dam floods

Answer 17

• blockage by mass movement, glaciers, lava flows
• upstream: flood due to ponding
• downstream: outburst flood: flooding when dam fails
  peak discharge ~ 10 times greater that hydrometeorological floods
• may cause enormous damage

Question 18

flooding frequency

Answer 18

• increasing flood frequency in canada reflects:
• population growth
• better reporting of disasters
• climate change
• models predict increased precipitation for most of canada

Question 19

storm rainfall flood weather conditions

Answer 19

• thick snowpack
• wet spring
• heavy rainfalls over a large area

Question 20

urbanization

Answer 20

• has created more hazardous conditions
• less infiltration where ground surface is covered with impermeable material
• development on flood plains
• flood impact can be reduced by careful land management
• restrict flood plains to recreational use

Question 21

flood control strucutres

Answer 21

• dams
• leeves: dikes that condone flood water by increasing the height of the channel
• floodway: artificial channel open to waterflow at peak discharge to handle excess volume