Flood Response

Question 1

The basics

Answer 1

• flow downhill under gravity
• flow velocity moderated by frictional resistance and sediment transport controlled by flow velocity and velocity profile
• flow depth can also vary significantly with channel cross-section and roughness

Question 2

Flood Propagation

Answer 2

downstream flood peak and timing

• if/when the flood will occur and how long the flood water is going to be there
• raised deeper water overtakes shallower water

Question 3

Catchment area

Answer 3

• small catchments, response times are short

- as catchment area increase the range of travel times to channel outlet increases

Question 4

Discharge

Answer 4

• determined by climate (precipitation and evapotranspiration, and storage factors)
• raised water level represents a disturbance which propagates down stream as a wave
• a higher discharge may equal earlier peak and therefore flooding
• higher discharge = higher rainfall

Question 5

Speed/Velocity

Answer 5

• raised water level/depth can be identified by the velocity of the flow, deeper the water, faster the flow
• higher velocity = increased flood activity

Question 6

Storage

Answer 6

• zones of potential storage gives lags in channels and on floodplains
• delays peak flow and reduces peak magnitude
• weirs and flood control dams function as local reservoirs

Question 7

Groundwater

Answer 7

• all pores are filled with water
• aquifers hold water
• effects on overland flow, subsurface flow and groundwater flow

Question 8

Cross sectional area

Answer 8

• water depth, channel slope, resistance, roughness and disturbance

Question 9

Hillslope

Answer 9

• steep V-shaped valleys increase runoff and pathway to stream
• infiltration may effect overland flow

Question 10

Vegetation

Answer 10

• intercept, store and transport water to subsurface
• highly vegetated areas are going to take more time to reach the catchment
• urbanised areas, impermeable rock will transport precipitation quicker through runoff

Question 11

Tributries

Answer 11

• collect all the water and transport it to the main stream

- more tributries = higher catchment rate

Question 12

Boscastle Floods

Answer 12

• prolonged heavy rainfall
• deep V shaped valley upstream
• impermeable surface in urban areas around catchment
• 2 major tributries, Valancy and Jordon
• reduction in trees and hedges