| Date | November 2019 | Marks available | 1 | Reference code | 19N.1.bp.1 |
| Level | SL and HL | Paper | 1 | Time zone | |
| Command term | Estimate | Question number | 1 | Adapted from | N/A |
Question
The following diagram shows the rainfall stores and flows within a drainage basin during a rainfall event.
[Source: International Baccalaureate Organization, 2019]
Estimate the percentage of rainfall shown as surface storage at the start of the rainfall event.
Estimate the number of hours during which overland flow is present in the drainage basin.
Outline one reason why interception decreases over time during the rainfall event shown in the diagram.
Explain three possible ways in which urban development might change how rainwater moves through a drainage basin such as this.
Markscheme
Around 40 (accept 39 to 41)
10 (hours )15 (minutes) (allow 10 to 10 hours 30 minutes)
Accept answers in decimal points (10.0–10.5)
There is a limit to how much water can be stored on leaf surfaces / on vegetation [1], and after a few hours of rainfall no more interception storage can occur [1].
Award [1] for each valid effect and [1] for further development of how this might change the movement/flow/storage of rainwater.
For example: Urbanization would remove vegetation and thus interception storage [1]; as a result, more rain will flow through the drainage basin [1].
Do not accept reference to dams and reservoirs.
Other possibilities include:
- May be more surface storage, as rainwater cannot drain away due to impermeable surfaces.
- Little infiltration of rainfall due to impervious concrete surfaces, increasing run-off
- Small soil storage, as little rainwater will filter downwards from the surface.
- Altered overland flow of rainfall due to drainage channels and gutters.
