1.A.4 - The Water Cycle

Question 1

What is a flood hydrograph?

Answer 1

Shows the change in discharge caused by a period of rainfall

Question 2

What are flood hydrographs used for?

Answer 2

• Find out discharge patterns/trends of a particular drainage basin
• Help predict flooding events, therefore influence implementation of flood prevention measures

Question 3

What is base flow?

Answer 3

the “normal” river level before a rainfall event

Question 4

What does the rising limb show?

Answer 4

The discharge rising as storm enters the drainage basin.

Question 5

What is peak discharge?

Answer 5

The highest flow in the channel for that event.

Question 6

What is the lag time?

Answer 6

The time taken from the peak rainfall to the peak discharge

Question 7

What does the receding limb show?

Answer 7

When the discharge begins to fall

Question 8

Features of a flashy storm hydrograph

Answer 8

• short lag time
• steep rising limb
• steep falling limb
• high peak discharge

Question 9

Features of a delayed storm hydrograph

Answer 9

• long lag time
• gentle rising limb
• gentle falling limb
• low peak discharge

Question 10

Physical factors affecting storm hydrographs

Answer 10

The drainage basin’s slope/gradient - DBs with steep sides have a faster overland flow and therefore gets to the river more quickly, causing a higher discharge and short lag time. Results in flashy hydrograph

Question 11

Physical factors affecting storm hydrographs

Answer 11

Rock type - if the soil or rock type in the river basin is impermeable, overland flow will be high as there will be less percolation and the soil will be saturated resulting in a shorter lag time -> flashy hydrograph.

Question 12

Physical factors affecting storm hydrographs

Answer 12

Drainage basin area - large drainage basins catch more precipitation so have a higher peak discharge compared to a smaller basin. Larger DB = longer lag time. Larger DB = flashy

Question 13

Human factors affecting storm hydrographs

Answer 13

Farming practices:
Exposed soil - after harvest, loose soil is washed into rivers which leads to the sedimentation of rivers. This results in less capacity in rivers so an increased flood risk.
Ploughing down slopes - furrows can act as small stream channels, increased runoff and shorter lag time, flashier hydrograph.

Question 14

Human factors affecting storm hydrographs

Answer 14

Landuse change:
Concrete and tarmac surfaces - surfaces are impermeable so there is no infiltration and no throughflow. This means there is an increased runoff, increased flood risk
Deforestation - reduces interception rates so rainwater hits the surface directly, leading to saturated soils which results in rapid overland flowed more runoff. Increased flood risk.

Question 15

Human factors affecting storm hydrographs - Water Abstraction

Answer 15

Happens when:
- high population density
- demand for food
- heavy industry
demand for water exceeds amount available during a certain period.
- low rainfall, high population density

Question 16

Human factors affecting storm hydrographs - Water Abstraction

Answer 16

• Boreholes take water from the groundwater store -> reduced
• lowers the water table
• reduced groundwater flow and through flow
• long term drop in river levels

Question 17

Human factors affecting storm hydrographs - Water Abstraction

Answer 17

• water taken directly from rivers
• can be for drinking water
• most taken for agriculture, irrigation
• decreases discharge
• increased runoff from farmland -> pollution