Hawaii Flood Damage Model — Non-NWM Path

Standard flood model pipeline (NWM + HAND) is CONUS-only. Hawaii uses a gauge-stage + FEMA FIRM zone approach.

Algorithm

  1. USGS instantaneous-value stage data fetched for 4 Oahu gauges (param 00060/00065). Wahiawa Reservoir peaked at 85.29 ft — above flood stage (84 ft).
  2. Buildings in FEMA FIRM flood zones (AE, VE, A, AH) assigned scenario depths above first-floor elevation: VE=5ft, AE=3ft, A=2ft, AH=1ft.
  3. Additional buildings below the corridor flood surface (50 ft NAVD88 along Kaukonahua Stream corridor) assigned elevation-based depths.
  4. HAZUS 6.0 depth-damage curves applied per occupancy type (RES1, RES2/MH, COM): damage_index = interpolated fraction of structure value damaged.
  5. Structure value from NSI (National Structure Inventory) via USACE.

Depth Assumptions

FEMA VE zone5 ft above FFE (coastal wave)
FEMA AE zone3 ft above FFE (100-yr riverine)
FEMA A zone2 ft above FFE (100-yr, no BFE)
FEMA AH zone1 ft above FFE (ponding)
Kaukonahua corridorElevation-based: 50 ft NAVD88 flood surface

Wahiawa Dam (Lake Wilson)

OwnerDole Food / Castle & Cooke
Capacity9,200 acre-ft (3 billion gal)
DLNR ConditionPoor — Very High risk
Peak reservoir level85.29 ft (flood stage: 84 ft)
OutcomeReceded without failure

References

USGS Water Services. Real-time gauges 16210000, 16210200, 16210500, 16340000.
FEMA NFIP FIRM. Flood Insurance Rate Map zones via NSI hazard fields.
HAZUS 6.0. Depth-damage curves, FEMA/NIBS 2022.
NSI v3. National Structure Inventory, USACE 2023.
Governor Josh Green estimate. $1B total event damage (March 20, 2026).
Buildings colored by inundation depth — FEMA FIRM zones + Kaukonahua corridor • HAZUS depth-damage • Click a building for details
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