Slide 1 of 7 · Settling starter · Geography · Year 8
5 minutesSynthesising Witness Accounts and River Data for a Flood Enquiry
After a river flood, local residents often have strong opinions about what caused the water to rise. Today you will cross-reference three witness statements from an invented flood in Pont y Glyn with the official river gauge hydrograph and rainfall table.
While the register is called: write your name, class and date on your worksheet, then read Section 1 of the stimulus sheet and answer the starter question in rough.
Starter question: Look at the storm hydrograph table in Section 1 of the stimulus sheet. At what time was peak rainfall (14:00), and at what time did the river reach peak discharge (17:30)? How many hours apart were they?
Slide 2 of 7 · Today’s brief and key words · Geography · Year 8
5 minutesToday’s brief and key vocabulary
Pont y Glyn Community Council is holding a flood enquiry after the Afon Glyn burst its banks on 14 October. You will read the storm hydrograph data, test three witnesses’ claims, explain the effect of the new retail car park, and write a 150-word enquiry summary.
Hydrograph terms
- Discharge (cumecs): cubic metres of water flowing past the river gauge every second (m³/s).
- Bankfull discharge: the maximum flow the river channel can hold before flooding (40.0 cumecs).
- Lag time: the time delay between peak rainfall and peak river discharge.
Drainage basin & literacy
- Impermeable surface: tarmac or concrete that water cannot soak through, increasing rapid surface runoff.
- Synthesis: combining evidence from multiple texts and data tables to reach a balanced judgement.
Slide 3 of 7 · Step 1: Reading the storm hydrograph · Geography · Year 8
10 minutesStep 1: Extracting the storm hydrograph figures
Use Section 1 of the stimulus sheet to complete the hydrograph table in Step 1(a) and calculate the lag time and flood duration in Step 1(b).
Worked formula for Lag Time:
Lag time = Time of peak river discharge − Time of peak rainfall
17:30 − 14:00 = 3 hours 30 minutes (3.5 hours).
Checking when the river flooded (above 40.0 cumecs bankfull):
Look down the discharge column in Section 1: the river reached 40.0 cumecs at 16:00, peaked at 52.0 cumecs at 17:30, and dropped back to 40.0 cumecs at 19:00.
Slide 4 of 7 · Step 2: Fact, opinion and witness cross-check · Geography · Year 8
10 minutesStep 2: Distinguishing fact from opinion and testing claims
Read the three witness statements in Section 2 of the stimulus sheet. Separate verifiable facts from personal opinions, and check each witness’s numbers against the river gauge data.
| Witness | Fact claim in statement | Does the gauge data support it? |
|---|---|---|
| Witness A: Siân Parry (Bakery owner) | Water came over the flood wall at 16:15; blames the new tarmac car park alone. | Timing supported: river passed 40.0 cumecs bankfull at 16:00 (43.5 cumecs by 16:30). Single-cause blame is opinion. |
| Witness B & Witness C | Complete the rows for Witness B (Mark Evans, Retail Park Manager) and Witness C (Dr Owen Rhys) on your worksheet... | |
Slide 5 of 7 · Step 3 & Step 4: Impermeable surfaces & enquiry summary · Geography · Year 8
12 minutesStep 3 and Step 4: Impermeable surfaces and your 150-word enquiry summary
First complete the cause-and-effect chain in Step 3 comparing the 2019 storm with the 2026 storm. Then write a balanced 150-word enquiry summary for Pont y Glyn Community Council in Step 4.
Structure for your Step 4 community council summary (around 150 words):
- What happened on 14 October: Quote total rainfall (48 mm), peak rainfall (18 mm at 14:00), peak discharge (52.0 cumecs at 17:30), and the 3.5-hour lag time.
- Evaluating the witnesses: Confirm Siân Parry’s 16:15 flood timing (river passed 40.0 cumecs at 16:00), and correct Mark Evans’s false claims (discharge at 14:30 was 18.0 cumecs, not flooding).
- Physical and human causes: Synthesise how saturated upland peat bog and the 4.5 hectares of impermeable retail park tarmac shortened the lag time from 5.0 hours to 3.5 hours and raised peak discharge from 38.0 to 52.0 cumecs.
Slide 6 of 7 · Partner and self check · Geography · Year 8
5 minutesCheck your enquiry report against the success criteria
Check your own worksheet or swap with your partner. Tick each box in the success criteria table only if the evidence is clearly written on the sheet.
- Have you calculated the 3 hour 30 minute (3.5 hour) lag time and the 3-hour flood duration (16:00 to 19:00) in Step 1?
- Have you separated fact from opinion and used gauge figures to refute Mark Evans’s 14:30 and 100 mm claims in Step 2?
- Have you explained how impermeable tarmac reduced infiltration, speeded up surface runoff and shortened lag time from 5.0 hours to 3.5 hours in Step 3?
- Does your Step 4 summary synthesise both physical and human causes in around 150 words with an objective tone?
Slide 7 of 7 · Plenary quick-check · Geography · Year 8
3 minutesPlenary: Quick-check answers
Check your answers against the summary table on the board before handing in your worksheet.
| Enquiry question | Verified answer |
|---|---|
| Peak rainfall, peak discharge and lag time (2026 flood) | Peak rain: 18 mm at 14:00 · Peak discharge: 52.0 cumecs at 17:30 · Lag time: 3 hours 30 minutes (3.5 hours) |
| Time window when the Afon Glyn exceeded 40.0 cumecs bankfull | 16:00 to 19:00 (3 hours above bankfull discharge) |
| Which witness gave inaccurate figures? | Witness B (Mark Evans): claimed 100 mm rain (actually 48 mm) and flooding at 14:30 (discharge was only 18.0 cumecs) |
| 2019 vs 2026 storm comparison (both 48 mm total rain) | After 4.5 ha of meadow became tarmac, lag time fell from 5.0 h to 3.5 h and peak discharge rose from 38.0 to 52.0 cumecs |