R - River Discharge (Factors affecting and hydrographs)

Question 1

What is river discharge?

Answer 1

The volume of water flowing in a river

Question 2

What is river discharge affected by?

Answer 2

Percipitation, hot weather (higher temp = lower discharge bc of evaporartion), removal of water (abstraction - reduces discharge)

Question 3

What do hydrographs do?

Answer 3

Show river discharge over a period of time - they show how the volume of water flowing at a certain point in a river changes over a period of time

Question 4

What do storm hydrographs do?

Answer 4

Show river discharge around the time of a storm event

Question 5

What is peak discharge?

Answer 5

The highest point on the graph, when the river discharge is at its greatest

Question 6

What is lag time?

Answer 6

The delay between peak rainfall and peal discharge

Question 7

Why does lag time happen?

Answer 7

Because it takes time for the rainwater to flow into the river

Question 8

What is the rising limb?

Answer 8

The part of the graph up to peak discharge

Question 9

What is the falling limb?

Answer 9

The part of the graph after peak discharge

Question 10

What are the physical factors that affect the storm hydrograph?

Answer 10

• Drainage basin characteristics - the physical features of the drainage basin
• The amount of waster already present in the drainage basin (‘antecedent moisture’)
• Rock type
• Soil type
• Vegetation
• Precipitation
• Temperature

Question 11

What does the drainage basins characteristics affect? Why?

Answer 11

Lag time and peak discharge

• Larger DB’s can catch more precipitation = higher peak discharge
• Smaller DB’s = shorter lag times because water has less distance to travel to reach the main channel
• Steep sided drainage basins = shorted lag times - water flows more quickly downhill (can also increase peak discharge)
• Circular basins are likely to have a flashy hydrograph - this is because all points on the watershed are roughly the same distance from the point of discharge measurement - meaning lots of water will reach the measuring point at the same time - increasing peak discharge
• Basins with lots of streams (high drainage density) drain quickly = shorter lag times

Question 12

What does the amount of waster already present in the drainage basin affect? why?

Answer 12

Lag time
- If the ground is already waterlogged - infiltration is reduced and surface runoff increases - meaning rainwater reaches the river more quickly which reduces lag time

Question 13

What does rock type affect? Why?

Answer 13

Lag time and peak discharge

• Impermeable rocks reduce infiltration and increases surface runoff - reducing lag time
• Peak discharge also increases as more water reaches the river in a shorter period

Question 14

What does soil type affect? Why?

Answer 14

Lag time and peak discharge
- Sandy soil allows lots of infiltration - but clay soils have low infiltration rates
Low infiltration rates increase surface runoff - reducing lag time and increasing peak discharge

Question 15

What does vegetation affect? Why?

Answer 15

Lag time and peak discharge

• Vegetation intercepts precipitation and slows its movement to the river channel - increasing lag time
• The more vegetation in a drainage basin - the more water is lost through (transpiration & evaporation) before it reaches the river channel - reducing peak discharge

Question 16

What does precipitation affect? Why?

Answer 16

Peak discharge

• Intense storms = more precipitation and so greater peak discharge
• The type of precipitation affects lag time - eg snow thats fallen in a winter storms can melt and flow into the river that spring

Question 17

What does temperature affect? Why?

Answer 17

Lag time and peak discharge

• Hot, dry conditions and cold, freezing conditions both result in dry ground - which reduces infiltration and increases surface run off (reducing lag time and increasing peak discharge)
• High temperatures can increase evapotranspiration - so less water reaches the river channel - reducing peak discharge

Question 18

How does human activity affect the hydrograph?

Answer 18

In urban areas the ground is often impermeable (eg concrete)
This increases surface runoff meaning water flows more quickly into the river - increasing peak discharge and reducing the lag time
- Man made drainage systems - water flows down drains onto the river before it can evaporate or infiltrate causing a shorter lag time and increased peak discharge