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Date May 2019 Marks available 4 Reference code 19M.1.bp.1
Level SL and HL Paper 1 Time zone
Command term Outline Question number 1 Adapted from N/A

Question

Option A — Freshwater

The diagram shows the changing frequency of discharge* in a small drainage basin during two different time periods.

[Source: © International Baccalaureate Organization 2019]

 

* frequency of discharge: how often a river reaches or exceeds a particular discharge level

Estimate the highest discharge of the river during the 1950s.

[1]
a.

State the number of times that river discharge reached 4 m3/s (cubic metres per second) during the 1990s.

[1]
b.

Outline two possible land use changes that could account for the increase in river discharge over time shown in the diagram.

[4]
c.

Explain how different channel modifications in a small drainage basin such as this can increase flood risk.

[2]
d.i.

Explain how different channel modifications in a small drainage basin such as this can assist with flood mitigation.

[2]
d.ii.

Markscheme

Award [1] for 6.3 (m3/s) (allow 6.2–6.4).

a.

Award [1] for 8 times.

b.

In each case, award [1] for a valid land use change (eg, urbanization, deforestation) that might explain increased river discharge, and [1] for how this could account for the increase shown. For example:

c.

Award [1] for a valid modification and [1] for further development of how this might increase flood risk.

For example: Straightening the river channel [1] allows faster removal of an increased amount of water away from the area, increasing flood risk downstream [1]

d.i.

Award [1] for a valid modification and [1] for further development of how this might decrease flood risk.

For example: Constructing man-made levees [1] increases channel capacity, allowing greater discharge without flooding [1].

As the question asks for "different modifications", do not accept the same modification twice.

Do not accept afforestation, changing agricultural practices or other land use changes.

d.ii.

Examiners report

There were no problems in identifying the correct figures.

a.

There were no problems in identifying the correct figures.

b.

A well answered question, with urbanization and deforestation the main land use changes considered for increasing river discharge.

c.

Generally well answered. Weaker candidates did not focus on channel modifications and/or confused parts (i) and (ii) in their responses.

d.i.

Generally well answered. Weaker candidates did not focus on channel modifications and/or confused parts (i) and (ii) in their responses.

d.ii.

Syllabus sections

Option A: Freshwater » A.2. Flooding and flood mitigation » A.2.2. How urbanization, deforestation and channel modifications affect flood risk within a drainage basin
Option A: Freshwater » A.2. Flooding and flood mitigation
Option A: Freshwater

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