The issue: A Damming report – why are some strategies for flood management more sustainable than others?

Look through the resource booklet What information do you need to know? Write it down in your books Share your ideas with another pair

The basics! What is a river? What is a drainage basin? What is a flood? What causes a flood? What is a hydrograph? What is resource 1 about? What possible questions could we be asked?

Task 1 What is a drainage basin? Why is this relevant to the exam? You need to know the following terms.

What is a drainage basin? Tributary A river which joins a larger river. Mouth Where the river flows into the sea, or sometimes a lake. Catchment The area from which water drains into a particular drainage basin. Watershed The boundary dividing one drainage basin from another- a ridge of high land. Source The upland area where the river begins. Confluence The point at which two rivers join.

Do you know your drainage basin terminology?

You also need to know what a drainage basin looks like on a map

Match the label to the correct letter Watershed c Confluence Tributary b Source d a

Sketch the river showing its catchment Add the following labels – Watershed, Confluence, Tributary

Examination question Study the map of a river valley below: X Y Height (m) X Y X Y Sketch a cross-section of the river valley from X to Y. Label two features of this river valley. State at what stage of a river’s course you would expect to find this type of valley. Give reasons for your answer.

What is a river? How does water enter a river? Why would a river flood?

The water cycle – more detailed

The water cycle – definitions!

You need to understand water enter a river in order to understand how it floods

The drainage basin

Drainage basin system interception infiltration surface runoff precipitation interception evapotranspiration infiltration surface runoff throughflow percolation river water table groundwater flow

What is a hydrograph? What information does it provide? What do the key terms mean?

What is a flood hydrograph?

Hydrographs Peak discharge Falling limb Rising limb storm flow normal (base) flow I = Lagtime Peak rainfall Write a definition of the key words. Calculate the lagtime shown on this hydrograph.

What would a hydrograph look like if it was about to flood? What is a flood? Why do rivers flood? Complete the work sheet about what causes flooding

What affects the shape of a hydrograph? Hydrographs Geology and soil Gradient of the valley sides What affects the shape of a hydrograph? Land use Drainage density Type and amount of precipitation

How do trees reduce flooding? trees intercept the rain evapotranspiration reduces the amount of water that reaches the river water is taken through the roots and so less enters the river

What factors influence the shape of a hydrograph? The hydrographs ‘a’ and ‘b’ have been produced from the same storm event but from different drainage basins.

Hydrographs Imagine that these two areas have had the same amount of rain over a 24-hour period. Draw a possible hydrograph for each of these areas. A B

Hydrographs What could cause 2 peaks in a hydrograph?

Resource 1 What else do you need to know? What type of questions could you be asked about this resource (use last years paper to help you) What is the lag time in each drainage basin? Which river is more likely to flood and why? Compare the 2 drainage basins and explain why are different.

Drainage basin 1: What does the word discharge mean? (1) What does the word lag time mean? (1)

It is the volume of water in cubic metres in the river every second. It is the time between the maximum rainfall and maximum discharge.

Describe the shape of the storm hydrograph in resource 1 (4).

Mark for shape and figures. 2 for rain/ 2 for discharge. The rainfall begins at 0mm at first, then increases to its maximum of 30mm after 1 hour, it then decreases back down to 0mm after 2 hours. The discharge begins at its minimum of 1m3/sec, then rises rapidly to a maximum of 14m3/sec after 3 hours, then decreases rapidly down after 5 hours, then remains fairly steady.

Describe the river valley shown in photo A. (2)

The river valley shows steep hills, and a grassy landscape with no trees. It is a rural area, and the river looks quite narrow.

Give the four and six figure grid reference that the photo is taken from. (2) How high is the tallest point shown on the map? (1) What direction did the photographer face to take the photo? (1)

8086 and 802867 600m East

Drainage basin B Describe the shape of the storm hydrograph in resource drainage basin 2 (4).

The rainfall begins at 0mm at first, then increases to its maximum of 30mm after 1 hour, it then decreases back down to 0mm after 40mins. The discharge begins at its minimum of 1m3/sec, then rises gradually to a maximum of 4m3/sec after 5 hours, then decreases gradually down to 1.8m3/sec at 9 hours.

Describe the river valley shown in photo A. (2)

The river is fairly narrow and shallow, and there are lots of trees The river is fairly narrow and shallow, and there are lots of trees. There are some deciduous and coniferous trees.

Give the four and six figure grid reference that the photo is taken from. (2) How high is the tallest point shown on the map? (1) What direction did the photographer face to take the photo? (1)

8585 858858 481m East

Compare the hydrographs in drainage basin A and B.(2) (Give two differences)

In drainage basin A the maximum discharge is very high at 14m3/sec, whereas in B it is lower at 4m3/sec. In drainage basin A the rising and falling limb are very steep, whereas in B they are a much gentler curve. In both drainage basins the rain falls for about 1hur and 30mins. The lag time in photo A is 2 hours, whereas in Drainage basin B it is nearly 4 hours long.

Compare the lag time in both drainage basins (1) The lag time in photo A is only 2 hours, whereas the lag time in photo B is nearly 4 hours long. (1)

Explain why the lag time differs between drainage basin A and B. (4)

The lag time is shorter in A, this is because the land is steeper, so more water will travel by surface run off, which is quicker, so all the water will reach the river at the same time, whereas in photo B the land is flatter, so water will travel slower to the river. (2) There are less trees in A, so less water will be taken in by the roots and transpired back to the atmosphere, whereas in B there are lots of trees, so lots of water will be taken in by the roots and transpired. (2) In addition, the roots of the grass in photo A will be short, and will not hold the soil together, so it will be eroded, and will wash into the river, and fill it up with silt, so less water can be contained, whereas in photo B the tree roots will hold the soil together, so it doesn’t get washed into the river. (2)