Flood Hydrographs

Question 1

What is a flood hydrograph?

Answer 1

Used to represent rainfall for the drainage basin of a river and the river discharge on a graph.

Question 2

What are the key components of a flood hydrograph?

Answer 2

Discharge
Rising limb
Falling limb
Lag time
Baseflow
Stormflow
Bankfull discharge

Question 3

What is discharge in a flood hydrograph?

Answer 3

The volume of water passing through a cross-sectional point of the river at any point in time.
Measured in Cumecs (cubic metres per second). Made up of the baseflow and stormflow

Question 4

What is the rising limb in a flood hydrograph?

Answer 4

The line on the graph that represents the discharge increasing

Question 5

What is the falling limb in a flood hydrograph?

Answer 5

The line on the graph that represents the discharge decreasing

Question 6

What is the lag time in a flood hydrograph?

Answer 6

The time between peak rainfall and peak discharge

Question 7

What is the baseflow in a flood hydrograph?

Answer 7

The level of groundwater flow

Question 8

What is the stormflow in a flood hydrograph?

Answer 8

Comprised of overland flow and throughflow

Question 9

What is the bankfull discharge in a flood hydrograph?

Answer 9

The maximum capacity of the river. If discharge exceeds this this then the river will burst its banks and be in flood

Question 10

What is a flashy hydrograph?

Answer 10

Short lag time and high peak discharge, most likely occur during storm event.

Question 11

What is a subdued hydrograph?

Answer 11

Long lag time and low peak discharge

Question 12

What are the natural factors which create a flashy hydrograph? (9)

Answer 12

High intensity rainfall, antecedent rainfall, Impermeable underlying rock, High drainage density, small basin, circular basin, low temps, precipitation type, vegetation cover

Question 13

How does high intensity rainfall produce a flashy hydrograph?

Answer 13

Higher discharge potential. More likely for soil to reach its field capacity - increase surface runoff and decreasing lag time

Question 14

What is antecedent rainfall?

Answer 14

Rainfall that occurs before the studied rainfall event

Question 15

How does antecedent rainfall cause a flashy hydrograph?

Answer 15

Ground is saturated and soil reached field capacity - increased surface run off

Question 16

How does impermeable underlying geology cause a flashy hydrograph?

Answer 16

Decreased percolation - greater levels of throughflow

Question 17

How does high drainage density cause a flashy hydrograph?

Answer 17

Many tributaries to main river, increasing speed of drainage and decreasing the lag time

Question 18

How does a small basin cause a flashy hydrograph?

Answer 18

Rainfall reaches the central river more rapidly - decreasing lag time

Question 19

How does a circular basin cause a flashy hydrograph?

Answer 19

Rainfall reaches the central river more rapidly, decreasing lag time

Question 20

How do lower temperatures cause a flashy hydrograph?

Answer 20

Less evapotranspiration so greater peak discharge

Question 21

How does precipitation type cause a flashy flood hydrograph?

Answer 21

Snow or hail takes time to melt before moving to the river, so rainfall increases flood risk

Question 22

How does vegetation cover cause a flashy hydrograph?

Answer 22

Forested areas intercept more rainfall, decreasing flood risk, but exposed areas will transfer water to the river more rapidly, decreasing lag time

Question 23

What are the human factors which create a flashy hydrograph? (3)

Answer 23

Urbanisation, Pastoral farming, deforestation

Question 24

How does urbanisation cause a flashy hydrograph?

Answer 24

More impermeable surfaces - increased runoff. Surface storage and infiltration reduced

Question 25

How does pastoral farming cause a flashy hydrograph?

Answer 25

Ground trampled - less infiltration - more surface runoff

Question 26

How does deforestation cause a flashy hydrograph?

Answer 26

Less interception - more surface runoff and greater flood risk