Hydrographs

Question 1

What is a river regime?

Answer 1

A graph showing changes in river discharge over the course of a year in responses to climactic change with the seasons e.g precipitation, temperature, evapotranspiration

Question 2

What is discharge?

Answer 2

The amount of water in a river flowing past a particular point expressed in metres cubed per second (cumecs)

Question 3

What do storm hydrographs show?

Answer 3

Changes in river discharge in response to a rainfall event - short term change

Question 4

What is a hydrograph?

Answer 4

A graph that shows river discharge and rainfall over time

Question 5

What is a flood?

Answer 5

When the capacity of a river to transport water is exceeded and water flows over its banks

Question 6

What is base flow?

Answer 6

The base flow of the river represents the normal day to day discharge of the river and the consequence of groundwater seeping into the river channel

Question 7

What is storm flow?

Answer 7

Storm runoff resulting from storm precipitation involving both surface and through flow

Question 8

What is bankful discharge?

Answer 8

The maximum discharge that a particular river channel is capable of carrying without flooding

Question 9

What is peak discharge?

Answer 9

The point on a flood hydrograph when river discharge is at its greatest

Question 10

What is peak rainfall?

Answer 10

The point on a flood hydrograph when rainfall is at its greatest

Question 11

What is lag time?

Answer 11

The period of time between the peak rainfall and peak discharge

Question 12

What are the factors affecting the shape of a hydrograph? (4)

Answer 12

Size of drainage basin
Vegetation
Valley side steepness
Soil Type

Question 13

How does the size of the drainage basin affect the hydrograph?

Answer 13

Small drainage basin = flashy
Large = subdued

Question 14

How does the amount of vegetation affect the hydrograph?

Answer 14

Bare = flashy (deciduos in winter, low levels of interception, rapid movement through system)
Forest = subdued (deciduous in summer, high levels of interception and slower passage through the system: more water lost to evaporation from vegetation surfaces)

Question 15

How does the valley steepness (relief) affect the hydrograph?

Answer 15

Steep valley = flashy (promote surface run-off)
Gentle sloped valley = subdued (allow infiltration + percolation)

Question 16

How does soil type affect the hydrograph?

Answer 16

Impermeable = flashy
Permeable = subdued

Question 17

What are the key physical aspects affecting a hydrograph? (8)

Answer 17

• Shape of drainage basin
• steepness of drainage basin
• high/ low density
• saturation
• impermeable/ permeable rock
• vegetation
• precipitation intensity
• large/ small drainage basins

Question 18

What are the key human aspects affecting a hydrograph? (5)

Answer 18

• deforestation/ afforestation
• Agriculture
• Urban areas
• Growing population
• urbanisation

Question 19

What are the characteristics of a flashy hydrograph? (3)

Answer 19

• short lag time
• high peak
• steep rising limb

Question 20

What are the characteristics of a subdued hydrograph? (3)

Answer 20

• long lag time
• low peak
• gently sloping rising limb

Question 21

How does drainage density impact hydrograph?

Answer 21

High = more streams + rivers/ unit area so water moves quickly to measuring point
LOw = few streams + rivers / unit so water more likely to enter ground and move slowly through basin

Question 22

How does human activity impact hydrograph? (3)

Answer 22

• Urbanisation producing impermeable surfaces
• Deforestation reduces interception
• Arable land, downslope ploughing

Question 23

How does little human activity impact storm hydrograph? (3)

Answer 23

Low population density, few artificial impermeable surfaces
Reforestation increases interception
Pastoral, moorland and forested land

Question 24

How do pre-existing (antecedent) conditions impact hydrograph?

Answer 24

Basin already wet from previous rain, water table high, soil saturated, so low infiltration/percolation

Basin dry, low water table, unsaturated soils, so high infiltration/percolation