Waiakoa Gulch Stream

Waiakoa Gulch Stream Kihei:

DESCRIPTION: Latitude 20°47’03.0″,   Longitude 156°27’32.2″.  NAD83 Maui County, Hawaii, Hydrologic Unit 20020000. Drainage area: 10.10 square miles (Source: https://waterdata.usgs.gov/nwis/inventory?site_no=16659000)

Waiakoa Gulch Stream Kihei. Courtesy of SouthMauiWetlands

“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

The Waiakoa Stream Catchment area includes several ranches and passes several Monsanto fields before crossing Pi’ilani Highway and reaching the flood plain. There it enters the Waiokoa Wetland, before finally entering the ocean.

Waiakoa Stream Catchment (far left side). Photo: S.Dorn

Waiakoa Gulch can also be inundated by large Wave, and High Surf Events: In this image, the Waiakoa Wetland and Bridge area are flooded by ocean-related wave -driven flooding.

Waiakoa-Stream-Bridge-at-South-Kihei-Road-flooded-by large-waves
Waiakoa-Stream-Bridge-at-South-Kihei-Road-flooded-by large-waves. Photo D.Dorn

The Waiakoa Gulch Stream can flood the surrounding land near the shoreline, These areas are the traditional Flood Plains for the gulch.  This image shows the flood’s footprint connecting Kealia Pond all the way to Kenolio Park and beyond.

Waiakoa Stream 2021 Flood. Image: South Maui Wetlands Study.

Lateral Flooding: Streams have cycles of high and low flow, During high-flow events such as Kona Storms floodwaters expand beyond the stream banks and flow laterally. This slows the water and allows suspended solids to fall out. After big flows, large amounts of sediments are left behind. Sometimes these deposits are several feet deep.

Waiakoa Stream’s December 2021, “Flooding Footprint”. Photo: D.Dorn