River management

Question 1

Define precipitation

Answer 1

Moisture falling from the atmosphere as rain, hail, sleet or snow

Question 2

Define discharge

Answer 2

The quantity of water that passes a given point on a stream or river bank - within a given period of time

Question 3

More precipitation = More ____

Answer 3

More precipitation = More discharge

Question 4

What is a hydrograph

Answer 4

A hydrograph shows how a river responds to a rainfall event.

This helps us to understand discharge patterns of a particular drainage basin

Question 5

What two graphs are hydrographs made up of

Answer 5

Bar chart = Rainfall

Line graph = Discharge

Question 6

Features of a hydrograph

Answer 6

Peak rainfall
Lag time
Rising Limb
Peak discharge
Falling limb
Base flow (normal flow)

x - axis - time (days and hours)
y- axis - discharge in cumecs

Question 7

What is peak discharge

Answer 7

The highest discharge in a given period of time

Question 8

What is lag time

Answer 8

The delay between peak rainfall and peak discharge

Question 9

What is rising limb

Answer 9

The increase in river discharge as rainwater flows into the river

Question 10

Falling limb -

Answer 10

The decrease in the river discharge as the river returns to its normal level

Question 11

What is the base flow

Answer 11

The normal flow of a river when its level is being sustained by groundwater

Question 12

Label a hydrograph

https://www.jkgeography.com/uploads/1/0/8/4/108433405/screen-shot-2018-01-21-at-16-34-56_orig.png

Answer 12

https://www.jkgeography.com/uploads/1/0/8/4/108433405/screen-shot-2018-01-21-at-16-24-02_orig.png

Question 13

Two types of hydrographs

Answer 13

‘Slow response’ hydrograph
‘Flashy response’ hydrograph

Question 14

Explain the features of a slow response hydrograph

Answer 14

Slow response = slow flow

Small amount of rainfall in a prolonged amount of time

There is a less steep rising limb as water is taking longer to enter the river channel

The lag time is long as the water is taking a long time to enter the river channel - the peak discharge is lower as water is lost to infiltration and interception

Question 15

Conditions that would result in a slow hydrograph

Answer 15

Areas with permeable materials, vegetation, gently sloping land, unsaturated soil, good drainage

Question 16

Describe the features of a flashy response hydrograph

Answer 16

flashy response aka storm hydrograph = quick flow

Large amount of rainfall in a short period of time

The rising limb is steep because rainfall has occurred in conditions that have caused a lot of surface run off (when the water flows on the surface instead of permeating in the ground). All rainwater rushes to the river at once

The lag time is short as water gets into the channel quickly due to a lot of surface runoff - therefore the time between rainfall and entering the river is short

The peak discharge is also high as the water has gotten into the river quickly and less water is lost -
High peak discharge as there’s lots of water

Question 17

Conditions which may result in a flashy hydrograph

Answer 17

Prolonged rainfall, which results in saturated soil. Therefore more surface runoff -

Clay soil so water cannot infiltrate

Steep valley/hill so water runs down faster - reducing lag time

Little vegetation leads to more surface runoff (less interception)

Urban area with lots of impermeable materials

Poorly farmed land = increased surface runoff

Question 18

What is flashy response

Answer 18

flashy response hydrograph is associated with sudden flooding called ‘flash floods’

Question 19

What is a slow response

Answer 19

normal rainfall event (low flood risk)

Question 20

State the physical and human factors that affect flood risk

Answer 20

Physical
Precipitation (Heavy rainfall, prolonged rainfall)
Geology (rock type)
Relief (changes in land height)

Human - land use

Question 21

What is flooding

Answer 21

Flooding occurs when a river’s level rises so much that it spills over its banks

Question 22

What does a shorter lag time result in

Answer 22

Shorter lag time = peak discharge is higher = flooding is more LIKELY TO OCCUR

Question 23

Explain how heavy rainfall affects flood risk

Answer 23

Heavy rainfall means that water arrives too quickly to infiltrate, so there’s a lot of surface runoff, which increases the discharge (into river channels)

Question 24

Explain how geology affects flood risk

Answer 24

Clay soils and some rocks e.g. granite and shale, are impermeable (they don’t allow infiltration), so surface runoff is increased (into river channels)

Question 25

Explain how prolonged rainfall affects flood risk

Answer 25

Prolonged rainfall can saturate the soil Any further rainfall can't infiltrate, increasing surface runoff into river channels

Question 26

Explain how relief affects flood risk

Answer 26

If a river is in a steep-sided valley, water will reach the river channel quicker because it can flow faster down the steep slopes - this rapidly increases discharge

Question 27

Explain how land use affects flood risk

Answer 27

Buildings are often made from impermeable materials (e.g. concrete) and surrounded by rounds made from impermeable surfaces (e.g. tarmac), increasing surface runoff Man-made drains then quickly transport runoff to rivers, increasing discharge Trees intercept rainwater on their leaves, which then evaporates. Trees also take up and store water from the ground. This means that curing down trees increases the volume of water that enters the river channel

Question 28

State some types of different management strategies (FOR FLOODING)

Answer 28

Hard engineering Soft engineering

Question 29

What is hard engineering

Answer 29

Man-made structures built to control the flow of rivers and reduce flooding

Question 30

Examples of hard engineering

Answer 30

dams and reservoirs, straightening, embankments, flood relief channels

Question 31

Explain the method of dams and reservoirs

Answer 31

Dams are barriers built across the rivers, usually in the upper course A reservoir (artificial lake) is formed behind the dam

Question 32

Adv. of dams and reservoirs

Answer 32

Reservoirs store water (e.g. after heavy rain), control water flow and prevent flood downstream They can also be used to generate hydroelectric power (HEP)

Question 33

Disadv of dams and reservoirs

Answer 33

Dams are very expensive to build. Creating a reservoir can flood existing settlements Material is deposited in the reservoir, not along the river's course, so farmland downstream can become less fertile.

Question 34

What is channel straightening

Answer 34

Meanders are removed by building straighter, artificial channels

Question 35

Benefits of channel straightening

Answer 35

Water leaves the area more quickly rather than building up, so flood risk is lower

Question 36

Disadvantages of channel straightening

Answer 36

Flooding may happen downstream instead. Faster-moving water may cause more erosion downstream

Question 37

What are embankments

Answer 37

Embankments are raised walls built along the river banks

Question 38

Adv. of embankments

Answer 38

The river can hold more water, so floods are less frequent

Question 39

Disadvantages to embankments

Answer 39

They are quite expensive there is a risk of sever flooding, if the water rises above the level of the embankments or if they break

Question 40

What are flood relief channels

Answer 40

Channels that are built to divert water around built-up areas or to divert excess water if the river level gets too high

Question 41

Advantages of flood relief channels

Answer 41

Gates on the channels mean that the release of water can be controlled, reducing flood risk

Question 42

Disadvantages of flood relief channels

Answer 42

There will be increased discharge where the relief channel rejoins the river (or joins another river), which could cause flooding in that area

Question 43

What is soft engineering

Answer 43

Soft engineering is schemes set up using knowledge of a river and its processes to reduce the effects of flooding

Question 44

What is flood warnings and preparation

Answer 44

The Environmental Agency issues flood warnings through various media (e.g. TV, radio, internet) Buildings are modified to minimise flood damage. Residents can prepare sandbags and flood boards prior to floods

Question 45

Advantages/benefits to flood warnings and preparations

Answer 45

Warnings give people time to move possessions upstairs, put sandbags in place or evacuate. This reduces the impact of flooding

Question 46

Disadv. to flood warnings and preparation

Answer 46

Warnings don't prevent floods People may not have access to the warnings Modifying buildings is expensive Preparation doesn't guarantee safety from a flood and it could give people a false sense of security

Question 47

What is flood plain zoning

Answer 47

Flood plain zoning are restrictions that prevents building on parts of a flood plain that are likely to be affected by a flood

Question 48

Adv of flood plain zoning

Answer 48

Flood risk is reduced since fewer impermeable surfaces are created (e.g. roads) The impact of flooding is also reduced as there are no buildings to damage

Question 49

Disadvantages of flood plain zoning

Answer 49

The expansion of an urban area is limited if there aren’t any other suitable building sites It can’t help in areas with existing buildings

Question 50

What are planting trees

Answer 50

Planting trees in the river valley increases the interception of rainwater (the lag time)

Question 51

Adv. of planting trees

Answer 51

Discharge and flood risk decrease This is because planting trees in the river valley increases the interception of rainwater (and lag time increases) Vegetation reduces soil erosion in the valley and provides habitats for wildlife

Question 52

Disadv. of planting trees

Answer 52

Less land is available for farming

Question 53

What is river restoration

Answer 53

River restoration is making the river more natural. For example by removing man-made levees, so that the flood plain can flood more naturally

Question 54

Adv. of river restoration

Answer 54

Discharge is reduced so there’s is less is less risk of flooding downstream Little maintenance is needed and there are better habitats for wildlife

Question 55

Disadv. of river restoration

Answer 55

Local flood risk can increase, especially if nothing is done to prevent major flooding.