Waiakoa Wetland

The Waiakoa wetland is located in the Moku of Kula (Kīhei) in the Ahupua’a of Pulehunui. It sits within the Waiakoa Gulch and has its outlet at Kalaepohaku beach. This wetland is located on the Kīhei floodplain and is just 0.2 miles from Kealia Pond.

 

In North Kīhei at the start of South Kīhei Road is a small bridge and a small wetland tucked in between two buildings. You can barely catch a glimpse of it as you drive down the road, but it is always full of water. This small pool is a spring-fed wetland that is a link in the water cycle of a large gulch that comes from higher elevations down to the sea. The wetland is actually a much larger area that is on both sides of the road. The road cuts across the very last part of the wetland. The major portion of the wetland is on the mauka side (upslope/mountainside) of South Kīhei Road. It is an area of scrubby undeveloped land that is covered with Kiawe trees and bushes. This large flat area is the stream’s flood plain, and where the wetlands naturally expand during rains. During high rainfall events, the floodwaters break the banks of the stream and spread out laterally outward along the floodplain, the footprint of the expanded flood zone extends to Kealia Pond to the north and includes Kenolio park and parts of Mai Poina Beach Park.

This area, local residents will remember, floods periodically and causes traffic problems. and even cars have been washed into the ocean here.  A few years ago, they closed the road for several months the road while they re-engineered a new “conspan” bridge here.

As you drive across this new bridge you actually dip down, as the bridge’s deck is lower than the surrounding roadway on either bank or the stream. The bridge is designed to flood and overflow across the roadway. A sign says, “turn around and don’t drown”.

This wetland has permanent water because it is spring-fed, so water is constantly flowing down this gulch albeit underground. Water from this wetland merges with the ocean continuously and affects local ocean conditions. You may also notice that this body of water is very often a muddy brown color, showing that it has received stormwater runoff from higher elevations.

You may also notice that the water does not flow directly into the ocean, but there is a sandbar/sand plug blocking the mouth of the stream at Kalaepohaku beach. This is a sandbar that protects the ocean from the stormwater flowing directly into it.

Filtering: The wetlands receive the dirty stormwater, and hold back the silt and soil, and allow the water to filter down through the sand and back into the ocean.

This unsung hero is fighting to keep our ocean clean every day and every night, 24/7/365.

Flooding: However whenever heavy rains are expected, the County sees fit to break open the sand plug to preemptively drain the wetland so that the water level does not rise and “cause problems” to surrounding properties. However, this entire area is on the flood plain, and has been a wetland for centuries, long before anyone built anything here, including the ancient Hawaiians.

Flood mitigation: Wetlands in their natural state are flood-mitigators and reduce the negative impacts of flooding. They take on massive amounts of water and give runoff the chance to be absorbed through the ground before entering the ocean. The solution to much of Kīhei’s coastal flooding issues is to protect, preserve, and restore the coastal wetlands and maintain their margins and gulches so that they can detain large amounts of stormwater just as nature intended.

Culture: The freshwater streams in this area were once considered to be so special, that high chiefs would reserve them for their exclusive use.

This wetland is a textbook example of how wetlands have been underappreciated and relegated to the margins of our communities. We should instead try to better understand their role and learn how to appreciate their massive contributions to the health and wellbeing of our ecosystem, and their vital function as ocean protectors.

Wildlife: According to the USFWS there are 5 species here that are protected by the Endangered Species Act (ESA), and 1 specie protected by the Migratory Bird Treaty Act (MBTA) that may occur and transit through this area, including, the Hawaiian Hoary bat, Hawaiian petrel, Newell’s shearwater, wedge-tail shearwater, and hawksbill turtle. The threatened green sea turtle may also occur and transit through the study area. There are many more species that are more common and use this estuarine muliwai and nearshore areas as their habitat. Including many species of endemic and endangered plants and insects.

About the Waiakoa Gulch: The wetland is just one part of the entire gulch and watershed system. The gulch is a watershed feature that includes large catchment areas upcountry, that funnel rainwater into streambed and down the slope toward the sea.

Narrow Stream Mouth: Unfortunately, the stream bed has been narrowed by development and the addition of a bridge at South Kīhei Road. This bridge acts as a choke point during floods, and catches debris. The debris coming downhill with the floodwaters, creates a plug at the bridge, which quickly forms a dam wall blocking the stream. The stream then flows sideways and creates a large pool. The fast-flowing floodwaters slow down as they hit the newly-formed lake, and they drop out their suspended sediments. This means that not only are the areas covered with water, but also that there are massive amounts of mud left behind after storms.  This storm in 2021 left behind massive amounts of mud, that closed down the road for about a week. These mud-floods are the result of poorly managed farmland upslope on the ranches in the Kīhei Highlands. All the topsoil is easily mobilized because there is a lack of groundcover, and the soil has been loosened by Cattle and feral ungulates such as deer and goats. The result is a “mud-flood” happening every time there is a decent amount of rain.  Unfortunately, this causes big problems for the wetlands and overwhelmed their ability to filter water. Wetlands can filter a fair amount of floodwater, but super-sized mud-floods are damaging to the wetlands and in turn the ocean.

Massive damage from Mud Floods:  There is a big cleanup after storms, because mud, debris, and flooding can affect properties and transport infrastructure.  Cars get stranded, houses flood, and roads are buried or damaged by floodwaters.

“The gulch originates on the eastern slopes of Haleakala at an approximate elevation of 4,900 feet AMSL and extends westward to the Pacific Ocean. Downslope from Piilani Highway to the east, the gulch receives a constant supply of brackish groundwater and surface water is always present at the South Kīhei Road project site (wetland), the gulch is usually blocked by a sand deposit at the ocean and forms a muliwai (brackish water pond) at the South Kīhei Road culvert site (wetland)”. MA-EFEA-Waiakoa-Gulch-Culvert-Replacement.pdf