Wrights Road Storage Ponds – breach flood animations

Screening-level dam-breach model (ANUGA on LINZ 1 m LiDAR). Not a certified assessment. See the repository README and SPEC for method and caveats.

East embankment breachPond 1 → Pond 2 cascade, 7.2 Mm³ released, peak ~2,100 m³/s. 4 h animation. East embankment breach – routed to Diversion RoadSame east cascade breach on the full 31.5 × 16 km domain, 12 h animation: the wave reaches Browns Road at 4.3 h, Two Chain Road at 5.4 h and Diversion Road at 7.5 h, then drains to the Waimakariri River. 69 km² inundated (Damwatch zone 73 km²). North embankment breachPond 1 → Pond 2 cascade through the Dixon Road embankment, 4.7 Mm³ released, peak ~820 m³/s. The flow turns east north of the east-breach corridor. 4 h animation. North embankment breach – routed to Diversion RoadSame north breach on the full 31.5 × 16 km domain, 12 h animation: Downs Road at 4.5 h, Browns Road at 5.9 h, Two Chain Road at 7.4 h and Diversion Road at 9.6 h. 49 km² inundated (Damwatch zone 66 km²). West embankment breachPond 1 piping failure only, 1.2 Mm³ released, peak ~235 m³/s. 4 h animation. Earthquake – all embankments fail at oncePostulated seismic failure at full supply (Alpine Fault Mw 8 or Darfield-type Mw 7 shaking): east, south, north, west and dividing embankments breach simultaneously with no warning. 7.4 Mm³ released, combined peak ~3,000 m³/s within 35 min. 4 h animation. Storm – breach during heavy rain, Eyre River in floodRainy-day combination: the east cascade breach opens after 2 h of 10 mm/h rain on saturated ground with the Eyre River already carrying 150 m³/s (assumed) where it crosses the flood corridor. Same breach as East, wetter plain, no river capacity to spare. 4 h animation after the breach.
Exploratory – water races, dewatering and tree shelterbeltsWhat if the ponds are dewatered down the irrigation races for 6 h before the breach, and what do the tall shelterbelts do to the flood? Near-field runs (14 × 9.5 km) with the races MR4, R2 and R3 (assumed names) and the tree belts from LiDAR canopy height in the model. Not part of the published results; race names, culvert treatment and tree roughness are assumptions. Cyan lines: races; green blocks: shelterbelts. Dewatering only – culverts open20 m³/s down the races for 6 h, no breach. MR4 and R2 carry it; the Dixon Road drain (R3) spills. Dewatering only – every culvert blockedSame flows with every road and track crossing blocked: MR4 stalls 1.7 km from the ponds, R2 overtops its crossings and carries on. East breach after 6 h of dewatering – races running fullThe ponds are assumed to fail anyway (peak ~1,970 m³/s). 6 h of dewatering, then 4 h of breach flood. East breach onto dry races (comparison)Same breach and mesh without the dewatering flow: practically the same flood – full races change arrival by less than 5 min. East breach with tree shelterbeltsBelts over 6 m tall (median 14 m) as extra roughness (n = 0.20): 5–15 min later and 0.1–0.3 m deeper behind dense belts east of Carleton Road. East breach after dewatering, with tree shelterbeltsBoth together: races running full and shelterbelts in the model.
Results and mapsKey numbers for all breach scenarios, arrival-time comparison with Damwatch, and every hazard map (depth, speed, depth×velocity, hazard class, arrival time). Repository and handoverCode, configuration, specification and run instructions. Tripod Digital · September 2026 · LiDAR © Environment Canterbury / LINZ (CC BY 4.0) · Roads and buildings © OpenStreetMap contributors (ODbL)