hydrographs Flashcards
1
Q
what do hydrographs show?
A
The discharge versus time past a specific point in a river
2
Q
what is discharge
A
the volume of water flowing through a river channel
3
Q
what is lag time
A
how long it takes the peak rainfall to created peak discharge
4
Q
what is rising limb
A
line on a graph showing discharge increases
5
Q
what is falling limb
A
line on a graph showing discharge decreasing
6
Q
explain the physical causes of a shorter lag time ( 4 marks)
A
- 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
7
Q
explain the human causes of a shorter lag time (6 marks)
A
- 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
