The Ewa wetland is an example of a landlocked wetland. With no obvious overland outlets to the ocean, this wetland is still a catchment and detention basin and performs a vital function as drainage infrastructure. This neighborhood has no other stormwater drainage services, so this wetland takes all of the neighborhood’s rainwater.
This area has natural uncompacted, porous soils that are very efficient at infiltrating water into the water table and aquifer. These soil conditions allow large volumes of stormwater to be absorbed and stored below the surface rather than flowing directly into the ocean. This site has a very low elevation, averaging about 3.4 feet AMSL, which further supports its role as a natural collection point for water.
This wetland becomes a lake after heavy rains, as water flows into this area from many local sources, including Yee’s Wetland (orchard). This temporary expansion is a natural and expected condition, reflecting the wetland’s role as part of a larger interconnected drainage and groundwater system.
Ewa Wetland is part of a much larger group of wetlands that extend from the Piʻikea, Waipuilani, Yee’s, and VFW wetlands, with hydraulic connections to several others. These interconnected systems function together across the coastal plain rather than as isolated sites.
Groundwater Nexus: The Ewa wetlands are connected to many other wetlands through a series of underground pathways. It also communicates directly with the ocean and the aquifer in this area of Kihei. Whatever happens to the hydrology at this site affects the broader groundwater system and nearby coastal environments.
Natural Stormwater Retention Basin: The Ewa wetlands are the area’s de facto stormwater retention basin. As the lowest point in the surrounding neighborhood, this is where rainwater and floodwaters naturally accumulate. This site has the capacity to hold millions of gallons of stormwater during major rain events. After storms, large volumes of muddy water remain within this “muliwai” and slowly feed down into the aquifer over several days or weeks. This natural infiltration of stormwater through the ground filters out sediments and many contaminants before the water reaches the ocean, reducing direct impacts to the nearshore environment.
Wetland Services: The Ewa Wetland provides important services for the surrounding community as it mitigates and reduces the impacts from flooding. It also provides protection for the ocean waters and the nearshore ecosystems.
South Kihei Road Flooding and the “Bathtub Effect”
This section of South Kihei Road has no formal stormwater drainage infrastructure and sits at a natural low point in the landscape. As a result, it relies almost entirely on the Ewa Wetland as its drainage outlet. During heavy rains, stormwater flows toward this area as expected—but when that water is not able to enter the wetland, it backs up and begins to accumulate across the roadway and into surrounding properties.
This creates what is commonly referred to as the “bathtub effect,” where the road effectively becomes a holding basin for stormwater. As the water slows, heavy sediment and red silt settle out, leaving behind thick mud that can take weeks to fully dry or be removed. Each storm adds another layer, gradually raising the ground level and making future flooding worse.
The impacts are significant. Floodwaters spread across South Kihei Road, creating hazardous conditions for vehicles and pedestrians, while nearby homes—particularly along the mauka side—are vulnerable to repeated flooding and property damage. These are not isolated events; they are recurring conditions that reflect a breakdown in how stormwater is being managed in this area.
The images above and below document these conditions, showing what happens when stormwater cannot move through the system and reach the wetland as intended.
Ewa Wetlands Watershed Features
This diagram identifies a network of interconnected wetland and watershed features that function together across the Kihei coastal plain. The numbered sites represent mapped and recognized wetlands—including Ewa, VFW, Yee’s, and Piʻikea wetlands—as well as related retention areas and culturally significant sites such as Waiohuli Kai fishpond. These are not isolated locations; they operate as part of a shared hydrological system, where stormwater moves between sites through both surface flow and subsurface pathways. Collectively, these wetlands provide critical functions by receiving, storing, and redistributing stormwater across the landscape. They also support environmental and cultural resources that have existed long before modern development. The diagram illustrates how multiple sites contribute to this system, reinforcing that the effectiveness of any single wetland depends on the health and connectivity of the entire network.
Wetlands Identified in the Kihei Drainage Master Plan
The Kihei Drainage Master Plan identifies the Ewa Wetland and surrounding sites as part of a larger system of existing natural wetlands that function as stormwater infrastructure. These areas are not incidental open spaces—they are recognized components of how water is managed across the landscape.
As shown in the diagram above, stormwater runoff from developed areas is directed toward these wetlands, both through surface flow and underground pathways. Water moves between multiple wetland sites, forming an interconnected system that distributes and absorbs stormwater across the coastal plain. This system depends on maintaining clear flow paths so that water can reach these wetlands without backing up into surrounding neighborhoods.
These wetlands are relied upon to receive, hold, and gradually release large volumes of stormwater. When they are functioning properly, they reduce the intensity of flooding by spreading water out and slowing it down. However, they are not designed to eliminate flooding entirely—only to mitigate its severity and impacts.
When these wetlands are degraded, blocked, or prevented from receiving water, the system breaks down. Water that would normally flow into these areas instead backs up into streets and residential areas. This is why preserving these wetlands is not enough—they must also be maintained in a condition that allows them to function as part of the drainage system.
The impacts of this breakdown are visible in the images below, where local flooding reflects what happens when stormwater is unable to reach and move through these wetland systems as intended.
