Worked example · Geography · Year 8
LNF: Literacy → Reading → Understanding, response and analysis · DCF: Data and information literacy
A secure Year 8 response, annotated against the success criteria, and a full answer key for the supply teacher. Step 1: total rainfall = 48 mm; peak rainfall = 18 mm at 14:00; peak discharge = 52.0 cumecs at 17:30; lag time = 3 hours 30 minutes (3.5 hours); river was at or above 40.0 cumecs bankfull from 16:00 to 19:00 (3 hours); peak was 12.0 cumecs above bankfull. Step 2: Witness A’s timings (16:15 flood start, 17:30 peak) match the gauge data, though her single-cause blame is opinion; Witness B’s claims of 100 mm rain and flooding at 14:30 are refuted by the gauge (48 mm total rain; discharge at 14:30 was only 18.0 cumecs); Witness C’s figures match Section 3. Step 3: lag time shortened by 1 hour 30 minutes (1.5 hours) from 5.0 h to 3.5 h, and peak discharge rose by 14.0 cumecs from 38.0 to 52.0 cumecs.
| Hydrograph measurement | Value and unit (use 24-hour clock times) |
|---|---|
| Total storm rainfall between 12:00 and 16:00 (mm) | 2 + 12 + 18 + 10 + 6 = 48 mm |
| Time and amount of peak rainfall (mm) | 14:00 · 18 mm |
| Time and amount of peak river discharge (cumecs) | 17:30 · 52.0 cumecs (m³/s) |
| Lag time (Time of peak discharge − Time of peak rainfall) | 17:30 − 14:00 = 3 hours 30 minutes (3.5 hours) |
| Time the river first reached 40.0 cumecs bankfull and time it dropped back to 40.0 cumecs | Reached bankfull at 16:00 · Dropped back to bankfull at 19:00 |
| Total number of hours the river stayed at or above 40.0 cumecs (flood duration) | 19:00 − 16:00 = 3 hours |
(b) At its 17:30 peak, the river was 52.0 − 40.0 = 12.0 cumecs above bankfull discharge.
Reads the hydrograph table accurately, calculates the 3 hour 30 minute lag time and 3-hour flood window, and includes correct units (mm, cumecs, hours). Evidences criterion 1.
| Witness | One factual claim they make (times or numbers) | One opinion or biased phrase in their statement | Does the river gauge data support their factual claim? (Quote numbers) |
|---|---|---|---|
| Witness A: Siân Parry (Bakery owner) |
Water poured over the flood wall at 16:15 and reached 30 cm deep by 17:30. | “100% the fault of the greedy new Glanrafon Retail Park... worst planning disaster” | Supported: the river reached 40.0 cumecs bankfull at 16:00 (43.5 cumecs by 16:30), so overflowing at 16:15 and peaking at 17:30 (52.0 cumecs) matches the gauge. |
| Witness B: Mark Evans (Retail Park Manager) |
Over 100 mm of rain fell in 4 hours, and the river was already overflowing onto High Street at 14:30. | “Freak tropical monsoon... shopkeepers are just looking for someone rich to blame” | Refuted (False): total rain was 48 mm (not 100 mm), and at 14:30 river discharge was only 18.0 cumecs (22.0 cumecs below the 40.0 cumecs flood level). |
| Witness C: Dr Owen Rhys (Hydrologist) |
Both 2019 and 2026 storms had 48 mm of rain, but lag time fell from 5.0 h to 3.5 h and peak flow rose from 38.0 to 52.0 cumecs. | None (uses an objective, balanced scientific tone). | Supported: every figure matches the official 2019 and 2026 gauge records in Section 1 and Section 3. |
(b) Witness A’s bakery was damaged by floodwater, so she wants someone held responsible for her financial losses. Witness B manages Glanrafon Retail Park and wants to deflect blame away from his company’s car park so they do not face bad publicity or have to pay for flood defences.
Separates verifiable time and volume claims from emotive language and vested interests, using exact gauge figures (48 mm, 18.0 cumecs at 14:30) to expose Witness B’s false claims. Evidences criterion 2.
(a) Changes between the 2019 storm and the 2026 storm:
Lag time change: 5 hours 0 minutes − 3 hours 30 minutes = shortened by 1 hour 30 minutes (1.5 hours).
Peak discharge increase: 52.0 cumecs − 38.0 cumecs = increased by 14.0 cumecs (pushing the river from 2.0 cumecs below bankfull to 12.0 cumecs above bankfull).
(b) Step-by-step drainage basin explanation: In 2019, the 4.5-hectare riverside meadow had permeable soil and grass, allowing rainwater to soak into the ground by infiltration and travel slowly towards the river as throughflow. When the meadow was covered in impermeable tarmac in March 2026, rainwater could no longer infiltrate the ground. Instead, water flowed rapidly over the smooth tarmac as surface runoff and straight through storm-drain pipes into the Afon Glyn. Because the water reached the river channel 1.5 hours faster, the lag time shortened from 5.0 hours to 3.5 hours and all the water arrived at once, raising peak discharge from 38.0 to 52.0 cumecs.
Quantifies both changes between 2019 and 2026 and links impermeable tarmac to reduced infiltration, rapid surface runoff, shorter lag time and higher peak discharge. Evidences criterion 3.
Pont y Glyn Flood Enquiry Summary (14 October 2026)
On 14 October 2026, 48 mm of rain fell between 12:00 and 16:00, with peak rainfall of 18 mm at 14:00. The Afon Glyn exceeded its 40.0 cumecs bankfull threshold from 16:00 to 19:00, reaching a peak discharge of 52.0 cumecs at 17:30 after a lag time of 3 hours 30 minutes.
Gauge records confirm bakery owner Siân Parry’s account that flooding began around 16:15 and peaked at 17:30. Conversely, retail park manager Mark Evans’s claims of 100 mm of rain and flooding at 14:30 are false: at 14:30, river discharge was only 18.0 cumecs.
The flood resulted from both physical and human causes. Three weeks of autumn rain had saturated upland peat bogs, reducing natural infiltration. However, comparing 2026 with an identical 48 mm storm in 2019 proves that replacing 4.5 hectares of riverside meadow with impermeable car-park tarmac shortened the lag time from 5.0 to 3.5 hours and raised peak discharge from 38.0 to 52.0 cumecs. (158 words)
Maintains an objective, authoritative tone within the 150-word target, synthesising hydrograph timings, witness verification, physical saturation and human land-use change. Evidences criterion 4.