1.3.1 flooding

Question 1

what is a drainage basin?

Answer 1

the area of land drained by the river.

Question 2

what is a catchment area?

Answer 2

the area within the drainage basin.

Question 3

what is watershed?

Answer 3

the edge of highland surrounding a drainage basin.

Question 4

what is the source?

Answer 4

the beginning of the river.

Question 5

what is the confluence?

Answer 5

the point where two rivers or streams meet.

Question 6

what is a tributary?

Answer 6

a stream or smaller river that joins a larger one.

Question 7

what is a river mouth?

Answer 7

the point where the river ends, usually at the sea.

Question 8

what is precipitation?

Answer 8

any form of water or moisture that comes from a cloud, eg. rain

Question 9

what is interception?

Answer 9

precipitation that doesn’t reach the soil and is intercepted by vegetation, leaves/branches, buildings and concrete before reaching the soil. it is only temporary and quickly evaporated.

Question 10

what is infiltration?

Answer 10

water on the ground surface goes into soil and moves downwards.

Question 11

what is groundwater flow?

Answer 11

the process by which water flows through rocks.

Question 12

what is throughflow?

Answer 12

the movement of water downslope within the soil layer.

Question 13

what is overland flow?

Answer 13

(surface run-off) the movement of water over the land surface when the ground is saturated or frozen or when precipitation is too intense for infiltration to occur.

Question 14

what happens to cause flooding?

Answer 14

• water reaching the river channel quickly

- the river overflowing onto the floodplain

Question 15

what are the reasons for flooding in terms of climate?

Answer 15

• climate (heavy rainfall)
• no infiltration and therefore water runs off the surface
• occurs after heavy rainfall (in britain it occurs after thunderstorms in summer)
• this causes a flash flood
• snowmelt happens quickly causing a flood
• the ground may still be frozen so no infiltration occurs

Question 16

what does impermeable mean?

Answer 16

water cannot get through, eg. concrete or granite.

Question 17

what does permeable mean?

Answer 17

water can get through, eg. sandstone

Question 18

where is a flood risk greater in terms of geology?

Answer 18

where there is impermeable rock or soil.

Question 19

what is relief?

Answer 19

the shape of the land around us.

Question 20

what do steep slopes do to rainfall?

Answer 20

channel heavy rainfall downwards quickly into rivers due to gravity.

Question 21

how does vegetation affect flooding?

Answer 21

• trees, wood and forests intercept rainfall and take it into their roots
• trees delay the time water gets into a river
• farmland helps water infiltrate the soil and delay the time water gets into the river

Question 22

how does human activity affect flooding?

Answer 22

• deforestation means delay times are reduced. higher risk of flooding
• urban growth leads to more flooding
• tarmac and concrete on roads and pavements are impermeable so surface runoff is increased
• water gets into rivers faster

Question 23

what is peak rainfall?

Answer 23

the time of highest rainfall.

Question 24

what is peak discharge?

Answer 24

the time when a river reaches it’s highest flow.

Question 25

what is lag time?

Answer 25

the time water takes to reach the river.

Question 26

what is the base of a river?

Answer 26

the normal flow

Question 27

what is the rising limb?

Answer 27

the rising water flow in a river.

Question 28

what affects the rising limb?

Answer 28

• vegetation
• rock type
• slope
• situation (eg. urban or rural river)

Question 29

what is a falling limb?

Answer 29

shows that water is reaching the river but in decreasing amounts.