Water - Storm / Flood Hydrograph

Question 1

What is a storm hydrograph?

Answer 1

A graph showing us the discharge of a river leading up to and following a rainfall or storm event.

Question 2

What are storm hydrographs useful for?

Answer 2

Prediciting the response from rivers to a rainstorm, helping to manage the river.

Question 3

What is the lag time in storm hydrographs?

Answer 3

The time taken from peak rainfall to peak discharge.

Question 4

What are the characteristics of a flashy hydrograph?

Answer 4

Short lag time.
High peak discharge.
Steep rising and falling limbs.

Question 5

What type of hydrograph are more circular drainage basins likely to have? And why?

Answer 5

More flashy ones because each point on the drainage basin is relatively equidistant to the measuring point on a river.

Question 6

What type of hydrograph is a steep sided drainage basin likely to have? And why?

Answer 6

More flashy ones because water flows quicker on steep slopes.

Question 7

What type of hydrograph is a high drainage density drainage basin likely to have? And why?

Answer 7

More flashy ones because they have a lot of surface streams acting as tributaries to the main river. All water will reach the measuring station at the same time.

Question 8

What will happen if a drainage basin is already saturated by antecedent rainfall during a rainfall period?

Answer 8

Overland flow will increase because infiltration capacity will have been reached.
Time lag will be reduced.

Question 9

What will happen after a rainfall period if the soil or rock type is impermeable?

Answer 9

Overland flow will increase and throughflow and infiltration will be reduced causing a flashy hydrograph.

Question 10

What are some of the physical factors which affect the shape of the storm hydrograph?

Answer 10

Drainage density.
Bank gradient.
Soil or rock type.
Vegetation cover.
Intensity of precipitation.
Type of precipitation.
Size/shape of drainage basin.

Question 11

What are some human factors which affect the shape of the storm hydrograph?

Answer 11

Deforestation.
Afforestation.
Agriculture.
Land use.
Growth of urban areas.

Question 12

How does vegetation cover affect the shape of the storm hydrogrpah?

Answer 12

Vegetation intercepts precipitation and water is also lost due to evaporatio and transpiration from vegetation which increases lag time and reduces peak discharge.

Question 13

How does the intensity of precipitation affect the shape of a storm hydrograph?

Answer 13

It will result in a higher discharge.

Question 14

How does the type of precipitation affect the shape of a storm hydrograph?

Answer 14

Snow will cause a longer lag time in comparison to rain as it takes time to melt before entering the channel.

Question 15

How does the size of the drainage basin affect the shape of a storm hydrograph?

Answer 15

Larger drainage basins catch more precipitation and have a higher peak discharge in comparison to smaller drainage basins.
Smaller drainage basins will have a shorter lag time as precipitation has less far to travel.

Question 16

How does deforestation affect the shape of the storm hydrograph?

Answer 16

Deforestation reduces interception rates and the lack of roots will reduce the infiltration rate causing rapid overland flow and a flashy hyrograph.
Exposes soil to erosion which leads to sedimentatio of the channel, reducing the bankfull capacity of a river and increase risk of flooding.

Question 17

How does afforestation affect the shape of the storm hydrograph?

Answer 17

Increases interception rates and infiltration rates in the soil, preventing overland flow.
Prevents soil erosion which reduces the risk of flooding.

Question 18

How does ploughing affect the shape of the storm hydrograph?

Answer 18

Ploughing breaks up topsoil and allows for greater infiltration but also increases sedimentation of channels, promoting flooding.