| Date | November 2017 | Marks available | 6 | Reference code | 17N.2.sl.02 |
| Level | SL only | Paper | 2 | Time zone | |
| Command term | Explain | Question number | 02 | Adapted from | N/A |
Question
The diagram shows a storm hydrograph for a river.
[Source: © International Baccalaureate Organization 2017]
State the lag time for the storm event shown on the hydrograph.
State how many hours the discharge was over 40 cumecs.
Outline why the rising limb on this hydrograph is steeper than the falling limb.
Explain the formation of two landforms on a river floodplain.
Discuss the environmental consequences of eutrophication and the pollution of aquifers.
Markscheme
10–11 hours [1]
5 hours 30 minutes (5.5 hours) [1]
Accept answers in the range 5–6 hours [1].
The rising limb is steeper as it is responding to the precipitation falling in the drainage basin/rapid increase of rainwater reaching the river/rapid run-off [1], whereas the falling limb still has rain reaching the river slowly/by throughflow / groundwater flow [1].
Possibilities include, but are not limited to:
- floodplain
- meanders
- ox-bow lakes
- deltas
- levees
- terraces
- alluvial fans.
Award [1] for each landform identified and [2] for further description/explanation of their formation.
For example: Braiding [1] is a river channel with a number of interconnecting channels separating the islands or eyots [1]. They form when sediment-rich rivers are forced to deposit their load as discharge is reduced [1].
Groundwater pollution and eutrophication may be caused by farming, fertilizer and waste run-off. Eutrophication occurs in a surface water store, causing algal blooms and reduced levels of oxygen in the water, whereas aquifer pollution results in the declining quality and quantity of water.
Other environmental consequences could include adverse impacts on habitats, flora and fauna, or creation of dead zones.
Good answers may compare environmental consequences on a variety of scales or from different perspectives (stakeholders). Another approach might be to compare the way eutrophication occurs at a more local scale than aquifer pollution, or the way eutrophication occurs on the surface whereas aquifer pollution occurs underground.
At band D, expect description of the two types of pollution and their environmental consequences.
At band E, expect either a more detailed explanation of the consequences or a structured discussion of the two types of pollution.
At band F, expect both of these elements.
Marks should be allocated according to the markbands.
