hydrographs

Question 1

what do hydrographs show?

Answer 1

The discharge versus time past a specific point in a river

Question 2

what is discharge

Answer 2

the volume of water flowing through a river channel

Question 3

what is lag time

Answer 3

how long it takes the peak rainfall to created peak discharge

Question 4

what is rising limb

Answer 4

line on a graph showing discharge increases

Question 5

what is falling limb

Answer 5

line on a graph showing discharge decreasing

Question 6

explain the physical causes of a shorter lag time ( 4 marks)

Answer 6

• heavy precipitation as the more precipitation there is the more saturated the soil becomes and therefore it will not be able to absorb more water quicker so surface run off will increase
• the gradient of the land if the land is steep it means rainwater moves at a faster rate via surface runoff into the river making them more prone to flash flooding

Question 7

explain the human causes of a shorter lag time (6 marks)

Answer 7

• impermeable surfaces means water can’t infiltrate into the soil so into the river (surface runoff) this increases the river discharge
• deforestation with no trees or vegetation to infiltrate into the soil there is more water hitting the ground rapidly causing surface runoff
• but also without trees the soil is eroded quicker as the top layer of soil is left exposed to the sun causing it to dry out when it rains this finds its way into rivers and blocks them reducing their river channel capacity
• agriculture means cattle trample the soil meaning it compacts and stops rain infiltrating into the soil leading to an increase in surface runoff