Rivers, Floods and Management

Question 1

Drainage basin inputs?

Answer 1

Precipitation - rain, hail, snow, frost, dew

Question 2

Drainage basin storage’s? Give 3?

Answer 2

Interception - when precipitation lands on vegetation, buildings or concrete before reaching the soil. This is only temporary because the water evaporates quickly.

Vegetation storage - Water taken up by plants.

Surface storage - Water in puddles, ponds, lakes.

Groundwater storage - Water stored in the ground in soil or rocks. The water table is the top surface of the zone of saturation.

Channel storage - The water held in a river or stream.

Question 3

What is the technical term for water in puddles?

Answer 3

Depression storage.

Question 4

What is the technical term for water stored in soil?

Answer 4

Soil moisture.

Question 5

Name porous rocks which hold lots of water?

Answer 5

Aquifers.

Question 6

What is the zone of saturation?

Answer 6

The zone of soil and rock where all the pores in the soil or rock are full of water.

Question 7

Drainage basin Flows and Processes? Give 5 examples?

Answer 7

Surface runoff - Water flowing over land.

Throughfall - Water dripping from one plant to another.

Stemflow - Water running down a plant stem or tree trunk.

Throughflow - Water moving slowly downhill through the soil.

Infiltration - When water soaks into the soil. Infiltration rates are influenced by soil type and soil structure. During a storm water can’t infiltrate fast enough so flows over the surface.

Percolation - Water seeping down through soil to the water table.

Groundwater flow - Water flowing slowely through permeable rock below the water table.

Baseflow - Groundwater flow that feeds into rivers through river banks and river beds.

Interflow - Water flowing downhill through permeable rock above the water table.

Channel flow - The water flowing in the river of stream itself.

Question 8

Explain Flows and Processes?

Answer 8

The movement of water from one place to another.

Question 9

What is another name for channel flow?

Answer 9

The river’s discharge.

Question 10

Drain basin Outputs? Give 3 examples?

Answer 10

Evaporation - water to water vapour

Transpiration - Evaporation from plant leaves.

Evapotranspiration - The process of evaporation and transpiration together.

River discharge

Question 11

What does the water balance show?

Answer 11

The balance between inputs and outputs.

Question 12

Define River Discharge?

Answer 12

The volume of water flowing in a river.

Question 13

What do Hydrographs show?

Answer 13

The river discharge over a period of time.

Question 14

In regards to a Hydrograph, what is peak discharge?

Answer 14

The highest point of the graph, when the discharge is at its greatest.

Question 15

In regards to a Hydrograph, what is lag time?

Answer 15

The delay between peak rainfall and peak discharge. There is a delay because the water takes time to reach the river.

Question 16

In regards to a Hydrograph, what is rising limb?

Answer 16

The part of the graph up to the peak discharge. Discharge increases as rainwater flows into the river.

Question 17

In regards to a Hydrograph, what is falling limb?

Answer 17

the part of the graph after the peak discharge. Discharge decreases because less water flows into the river.

Question 18

Name and explain physical factors which effect a Storm Hydrograph? Name 5?

Answer 18

Drainage basin characteristics - effects the lag time and peak discharge. e.g larger drainage basins, steep sided drainage basins, circular basins.

The volume of water that is already present in the drainage basin affects lag time. If the soil is waterlogged then infiltration is reduced and surface runoff is increased.

Rock type - affects lag time and river discharge. Impermeable rock increases surface runoff, reducing lag time and increasing the river discharge.

Soil type - affects lag time and peak discharge. The rates of infiltration differ between soil types.

Vegetation - affects lag time and peak discharge. The more vegetation, the greater the interception and the longer the lag time. A greater number of plants also reduces the water that gets to the river as the plants absorb some for internal processes.

Precipitation - affects peak discharge. The larger the volume of precipitation the greater the river discharge.

Temperature - affects lag time and river discharge. High temperatures increase Evapotranspiration, reducing river discharge.

Question 19

How does human activity affect a hydrograph?

Answer 19

In urban areas the soil is convered by impermeable materials such as concrete. The water cannot infiltrate and thus, surface runoff is increased and the water flows into the river more quickly, shortening the lag time and increasing peak discharge.

Man-made drainage systems do the same, they transport the water to the river at a faster rate, reducing lag time and increasing peak discharge.

Question 20

What features of a river can erosion affect?

Answer 20

Length, Depth and Width

Question 21

Explain Hydraulic action?

Answer 21

The pressure of the water breaks rock particles away from the bed and banks of the river.

Question 22

Explain Abrasion/Corrasion?

Answer 22

Eroded rock scrapes against the bed and bank, removing material.

Question 23

Explain Attrition?

Answer 23

Eroded rocks smash into each other and break up into smaller fragments.The rock fragments also become more rounded.

Question 24

Explain Cavitation?

Answer 24

Air bubbles in turbulent areas of the river implode and send out shockwaves that break rock off the banks and bed.

Question 25

Explain Corrosion/Solution?

Answer 25

The dissolving of rock by chemical processes. Carbon dioxide dissolves in the water to create a weak acid which reacts with limestone and chalk.

Question 26

Explain solution?

Answer 26

Substances that can dissolve and are carried along by the river.

Question 27

Explain suspension?

Answer 27

Very fine material such as silt and clay.

Question 28

Explain saltation?

Answer 28

Larger particles such as pebbles or gravel. To heavy to be carried in suspension so instead bounce along the riverbed.

Question 29

Explain traction?

Answer 29

Very large particles such as boulders are pushed along the riverbed.