The wetland study site at 16 E. Waipuilani Road is located within Kihei’s Wetland District. This site was mapped during the 1965 wetland survey (Kolb), included in the 1991 Erickson wetlands survey, and is part of a larger interconnected wetland and watershed system extending throughout central Kihei. Wetland and watershed features occur on the east, west, and south sides of the property.
The site is located within a well-known flood-prone area that has experienced severe flooding on multiple occasions over the past several decades. It is one of the last undeveloped parcels in the area and occupies one of the lowest elevations within the local landscape. There is no formal area drainage, making the site an important low-lying catchment for surrounding floodwaters.
Watershed Services
This site currently provides important watershed services, including stormwater detention, temporary storage, and stormwater infiltration into the underlying aquifer. The site also exhibits numerous indicators of wetland hydrology, including altered vegetation, loose uncompacted soils, crusted mud, accumulated surface salt deposits, and seasonal groundwater expression.
One of the defining characteristics of this site is the interaction between surface water and groundwater. During heavy rainfall, floodwaters collect on the surface while groundwater can also rise through the soil as the water table responds to increased recharge. As floodwaters slowly recede, the site functions as an important infiltration area where stored surface water gradually returns to the aquifer.
Flood-Prone Area
This area is a notorious flood zone, partly because of its low elevation and primarily because this part of Kihei has no regional stormwater drainage system. Flooding may result from local rainfall, flash flooding from nearby gulches, elevated groundwater, or a combination of these factors.
Elevation
The elevation along South Kihei Road allows floodwaters from several local streams and drainage systems to spread north and south into the surrounding low-lying areas. The 16E Waipuilani site occupies one of the lowest elevations within this basin and receives runoff from surrounding neighborhoods.
The coastal dune system blocks direct drainage toward the ocean, causing floodwaters to backfill into the inland portions of the watershed.
Drainage Issues
As a result, stormwater can pond to depths of approximately 3 to 4 feet and remain for several days. Water gradually infiltrates through the soil into the aquifer, or Maui County may deploy pump trucks to remove floodwaters from surrounding neighborhoods.
There are currently no stormwater outlets serving this section of Kihei. This site also lies within a FEMA flood zone.
Different Sources of Flooding
Flooding at this location can occur from several different sources, including:
- Riverine flooding from overflowing streams and gulches.
- Surface runoff from surrounding developed neighborhoods.
- Rising groundwater associated with aquifer recharge.
- Coastal inundation from high wave events.
- Extreme high tides.
- Storm surge associated with severe coastal storms.
These flooding mechanisms often occur simultaneously, making this one of the more complex flood environments in South Maui.
Tsunami Hazard Zone
This area is also vulnerable to tsunami inundation. Even relatively small tsunami events have the potential to cross the beach park and flood nearby streets. Fortunately, larger tsunamis are rare, although smaller events of less than approximately six feet occur more frequently.
(NOAA Tsunami Hazard Zones)
Street Flooding
This area floods frequently and has no sidewalks or curbs. Floodwaters can create hazardous conditions for pedestrians, and vehicles have been known to stall or even float during major flooding events.
Mud and Silt
Following heavy rainfall, pooled floodwaters often leave behind significant accumulations of mud and silt. The area effectively functions as a temporary siltation basin, with deposits sometimes reaching one to two feet in depth. After floodwaters are removed, it typically takes several days before the mud dries sufficiently for cleanup operations.
Ingress and Egress During Flooding
Flooding can prevent residents from entering or leaving their properties. Standing water, deep mud, and road closures may isolate portions of the neighborhood for several days, creating significant disruptions to transportation and emergency access.
Vegetation
Vegetation includes several salt-tolerant and wetland-associated species, including ʻAkulikuli (Sesuvium portulacastrum), Kipukai / Enaena (Heliotropium curassavicum), Indian Fleabane (Pluchea indica), Buffel Grass (Cenchrus ciliaris), Kiawe (Prosopis pallida), Fan Palm (Livistona chinensis), and Koa Haole (Leucaena leucocephala).
Salt deposits and ʻAkulikuli (Sesuvium portulacastrum) at 16E Waipuilani.
Site Inspections and Aerial Surveys
This site has been identified through both aerial photography and repeated on-site inspections. It is believed to lie along a presumed underground groundwater pathway that follows E. Waipuilani Road, emerges at the ephemeral wetland within Waipuilani Park, and continues offshore through submarine groundwater springs along the shoreline.
The site’s mature trees also provide habitat for several protected species, including the Hawaiian Short-eared Owl (Pueo) and the Hawaiian Hoary Bat.
