Variations In Runoff And The Water Cycle

Question 1

Define river discharge.

Answer 1

The volume of water that flows in a river per second.

Question 2

What is river discharge measured in?

Answer 2

M^3/s
Cubic metres per second.

Question 3

What is a hydrograph?

Answer 3

Graphs of river discharge over time.

Question 4

What do hydrographs show?

Answer 4

• River discharge over time
• Volume of water
• River changes

Question 5

What is a flood hydrograph also known as?

Answer 5

Storm hydrograph

Question 6

What do flood hydrographs show?

Answer 6

River discharge around the time of a storm event over a short period of time of a storm event.

Question 7

Define peak discharge.

Answer 7

The highest point on the graph where river discharge is at its greatest.

Question 8

Define lag time.

Answer 8

The delay between peak rainfall and peak discharge (How long it takes rainfall to flow into the river).

Question 9

What would a shorter lag time do to discharge?

Answer 9

Increase peak discharge as more water reaches the river in a shorter period of time.

Question 10

Define the rising limb of a hydrograph.

Answer 10

The part of the graph up to peak discharge.

Question 11

Describe the falling limb on a hydrograph.

Answer 11

The area of the graph after peak discharge. It decreases because less water is now flowing into the river.

Question 12

What 4 factors affect the hydrograph shape?

Answer 12

-Size of drainage basin
-Shape of drainage basin
-Ground steepness
-Rock and Soil type

Question 13

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

Answer 13

Larger drainage basins catch more precipitation so they have a higher peak discharge but may have a longer lag time as precipitation may have to travel.

Question 14

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

Answer 14

Circular basins are more likely to have flashy hydrographs than long, narrow basins as all points of the watershed are the same distance away, meaning water will reach the river at the same time.

Question 15

Describe a flashy hydrograph.

Answer 15

A basin with rapid runoff and not much storage creates a hydrograph with a short lag time and high peak discharge.
This is a flashy hydrograph.

Question 16

How does ground steepness affect the shape of a hydrograph?

Answer 16

Water flows more quickly downhill on steep-sided basins = shortened lag time
Water also has less time to infiltrate so the runoff is higher.

Question 17

How does rock and soil type affect the shape of a hydrograph?

Answer 17

Impermeable rock= don’t allow infiltration.
= Higher surface runoff and higher peak discharge (more water reaches the river)

Question 18

What are the natural factors that cause variations in hydrographs and the water cycle?

Answer 18

-Storms
-Seasonal changes
-Vegetation

Question 19

How do storms affect hydrographs and the water cycle?

Answer 19

More precipitation= greater peak discharge.
Large input of rainfall causes flows such as runoff and stores like groundwater increase in size.
Some flows like infiltration may not occur rapidly enough for the size of the input increasing runoff.

Question 20

How do seasonal changes affect hydrographs and the water cycle

Answer 20

The size of inputs flows and stores varies with the seasons.
Winter: Water freezes so less flows
Spring: frozen water melts flows and outputs increase.

Question 21

How does vegetation affect variations in hydrographs and the water cycle

Answer 21

Vegetation intercepts precipitation and decreases surface runoff.
More vegetation there is the more water is lost through evapotranspiration reducing runoff and peak discharge.

Question 22

What are the human practices that impact hydrographs and the water cycle?

Answer 22

-Farming practices
-Land use change
-Water abstraction

Question 23

How do farming practices affect the variation in hydrographs and the water cycle?

Answer 23

Affects infiltration:
-Ploughing breaks up the surface meaning more water can infiltrate.
-Crops increase interception and decrease runoff
-Livestock compact soil decreasing infiltration and increasing runoff
-Irrigation can increase runoff if not all the water can infiltrate. Can cause river levels to fall.

Question 24

How does land use change affect hydrographs and the water cycle?

Answer 24

-Deforestation reduces the amount of water intercepted by vegetation increasing surface runoff.
-Construction of buildings and roads creates an impermeable layer that prevents infiltration increasing runoff.

Question 25

What is water abstraction?

Answer 25

When water is removed from a store to meet demand in areas that are highly populated.

Question 26

How does water abstraction affect hydrographs and the water cycle?

Answer 26

-More water abstracted during dry seasons for consumption and irrigation so stores are depleted and peak discharge decreases.