Screening-level results. Method, assumptions and caveats: SPEC.md §3 and §7.3; sources: source notes. Time zero for all 2D results is the moment the external (downstream) breach opens; for cascade scenarios that is 2.2 h after the Pond 1 failure begins.
| Scenario | Mechanism | Breach invert (LiDAR toe, m NZVD2016) | Peak outflow (m³/s) | Time to peak (h) | Volume released (Mm³) | Froehlich 1995 check (m³/s) |
|---|---|---|---|---|---|---|
| east | Pond 1 → Pond 2 cascade, overtopping | 210.8 | 2,098 | 1.1 | 7.18 | 1,484 |
| south | Pond 1 → Pond 2 cascade, overtopping | 215.4 | 1,066 | 1.5 | 5.34 | 777 |
| north | Pond 1 → Pond 2 cascade, overtopping | 216.7 | 817 | 1.7 | 4.68 | 600 |
| west | Pond 1 piping | 221.9 | 235 | 1.4 | 1.24 | 256 |
Damwatch (design report s3): "approximately 2,500 m³/s" for the type of breach analysed.
| Metric | East | West | Damwatch 2012 (E / W) |
|---|---|---|---|
| Inundated area > 0.1 m (km²) | 39.47 | 5.99 | flood zone 73 / 15 |
| Deepest water (m) | 2.9 | 1.7 | – |
| Fastest flow (m/s) | 5.5 | 1.8 | – |
| Buildings > 0.1 m / ≥ 0.5 m | 439 / 95 | 45 / 2 | households in zone 176 / at risk 40 ; 50 / 1 |
| PAR screening (2.5 persons per at-risk building) | 238 | 5 | 107 / 4 |
| Road | Damwatch arrival (h) | Model arrival (h) | Damwatch depth (m) | Model max depth (m) |
|---|---|---|---|---|
| Carleton Road | 1.50 | 0.77 | 0.68 | 1.00 |
| Wolffs Road | 2.08 | 1.33 | 0.33 | 0.94 |
| Poyntzs Road | 2.67 | 1.90 | 0.34 | 0.75 |
| Pesters Road | 3.00 | 2.27 | 0.57 | 0.51 |
| Downs Road | 4.17 | 3.33 | 0.3 | 1.18 |
| Browns Road | 5.25 | not reached in 4 h | 0.58 | 0.00 |
| Two Chain Road | 7.33 | not reached in 4 h | 0.46 | 0.00 |
| Diversion Road | 9.00 | not reached in 4 h | <0.1 | not reached in 4 h |
The model reaches each road ~45 min earlier and generally deeper than the 2016 study – the expected direction for uniform roughness (n = 0.045), a 20 m grid that smooths road/race embankments, and a 1.1 h breach formation. These are the phase-1 calibration levers.
| Road | First arrival (h) | Max depth (m) |
|---|---|---|
| Carleton Road | 1.93 | 0.37 |
| Wolffs Road | 2.86 | 0.30 |
| Wrights Road | 1.13 | 0.57 |
| Dixon Road | 0.64 | 0.71 |
| Domain Road | 1.10 | 0.50 |
Maximum depth
Maximum flow speed
Depth × velocity
Hazard class H1–H6
Arrival time
Time of peak depth
Maximum depth
Maximum flow speed
Depth × velocity
Hazard class H1–H6
Arrival time
Time of peak depth
With the design report's volumes and areas, Pond 1 draining into Pond 2 statically equalises at ~223.8 m RL, 0.5 m below the Pond 2 crest (224.3 m). The overtopping cascade Damwatch describes therefore requires dynamic surge or a different stage–storage shape. The model initiates the Pond 2 breach at 223.6 m RL (config/dam.yaml: cascade.pond2_trigger_mRL); reconcile with Appendix H before any reportable use.