The recent storm didn’t just bring flooding—it fundamentally altered the hydraulic capacity of South Maui’s entire stormwater system.
Across Kihei, we are now seeing widespread sediment deposition throughout critical drainage infrastructure. Stormwater drains, culverts, open channels, wetlands, and gulches are heavily impacted. This is not cosmetic—this is functional degradation of the system.
When sediment accumulates, it reduces channel conveyance capacity. That means the same volume of water that previously moved through these systems can no longer pass efficiently. The result is predictable: earlier overtopping, lateral spreading, and increased flooding into streets, homes, and neighboring properties.
Key Problem Areas Identified
- Waipuilani Gulch (South Kihei Road crossing):
The already undersized outlet is now further constricted by silt and debris loading. This chokepoint is one of the most critical failure nodes in the system. - Waipuilani Gulch Overflow Zones:
Sediment buildup has reduced the available floodplain storage and overflow routing capacity, increasing the likelihood of uncontrolled spillover. - Kalanihikoi Gulch:
In some areas, sediment banks have accumulated up to 6 feet in height, dramatically reducing the effective cross-sectional flow area of the main channel.
This forces stormwater to bypass the primary channel and instead spread laterally, increasing flood risk across adjacent land. - Storm Drains, Creeks, and Wetlands:
Catch basins, culverts, and natural drainage pathways are now partially filled with fine sediment (red silt “slurry”), reducing intake efficiency and accelerating blockage during high-flow events.
Why This Matters Now
This is not a long-term issue—it’s an immediate pre-storm vulnerability.
If these systems are not cleared before the next major rain event:
- Peak flows will exceed reduced capacities much faster
- Flow will divert out of intended channels
- Flooding will be more severe, more widespread, and more damaging than the last event
In hydrology terms, we are now operating with a compromised drainage network and reduced system resilience.
What Needs to Happen
We need urgent, coordinated action:
- Sediment removal (dredging and excavation) in gulches and channels
- Clearing of culverts, catch basins, and storm drain inlets
- Restoration of channel geometry and flow paths
- Inspection of all known chokepoints and undersized crossings
This is basic watershed management. If we ignore it, we are guaranteeing worse flooding next time.
Kihei’s drainage system depends on flow continuity from mauka to makai. Right now, that continuity is broken.
We don’t need another storm to expose the problem—we can already see it.
Now is the time to act.
