Kulanihakoi Gulch is located in the Hapapa watershed, in the Moku of Kula, on the leeward slopes of Haleakala, It begins high on the upper slopes of the mountain and winds downward all the way to the ocean through the coastal area known as Kula kai.
Location of Ranchlands in the watershed catchment areas.
Kulanihakoi Stream: The Gulch is formed by the Kulanihakoi Stream which is described as non-perennial. The stream itself stretches for more than 4 miles. Starting at about 8,000 feet above sea level, descending to sea level and below. It includes several tributaries including Kaipoioi Gl, Kaonoulu Gl, Naalae Gl, Kaakaulua Gl,
Comparison to Waipuilani Gulch: Kulinahakoi’s neighbor Waipuilani Gulch is conservatively 14,270 feet (2.7 miles) long, with a 10.5 square mile catchment area.
Upcountry Ranchlands: The muddy flooding problem’s source is the upcountry ranchlands with overgrazed degraded land and loose soils that are washed down in increasing quantities with each flood. Unfortunately, rainwater does not absorb into the now hydrophobic soils, it simply sheets off that land, and carries away massive amounts of soil.
Kulanihakoi Gulch: The gulch has a catchment (Drainage) area of 15.03 square miles (source USGS)
In Kihei, the Kulanihakoi gulch is prone to surface water flooding. Both public infrastructure such as roads and bridges and private property are damaged during storm events by sediment-laden stormwater. (Source SMWP 2019).
WETLANDS AT RISK: Flooding at Ka’ono’ulu-Kulanihakoi: Frequent flooding brings mudflows down the mountain. It should be noted, in each of these mudflows comes from the degraded ranchlands upcountry. Each storm brings thousands of tons of upcountry “mauka mud” down the mountain, and after storms.
MUD ACCUMULATION: this mud needs to be removed from the gulches and floodplains, otherwise, it increases flooding problems in neighborhoods, on roads, and/or flows into the ocean where it harms coral reefs. In the lower Gulch, the siltation has displaced the original stream flow and allowed it to overflow onto Kaonoulu road.
Department of Public Works: Cleaning up after every storm. The mud flowing down from the degraded ranchlands “mauka” of Pi’ilani Highway, clogs the Kulanihakoi streambed, causing stormwaters to overflow onto local roads, stopping traffic, and causing road closures. This mud needs to be cleared away from roads after storms. This photo is taken after December 2022 storm. Unfortunately, a lot of the mud is not removed, and over time it is allowed to accumulate in the streambeds and on the stream banks. The built-up of silt/mud causes future floods to be displaced and flow laterally. Each time they clean up the mud, they make the flooding problem worse. *This can also be seen at Waiakoa gulch where the post-cleanup berms are 4-6 feet higher than the pre-flood conditions.
New pathways: When we don’t remove all of the mud left over from mudfloods, each successive flood gets worse. The River finds new paths around previous flood paths and creates new outlets. The mud left behind in the river’s mainstream channel makes it less likely that the next flood will follow the same path.
Estimated Costs of Stream Restoration: The portions of Kulanihakoi, Waipuilani, and Keokea located makai of Pi’ilani Highway within the urban corridor of Kihei are good candidates for stream channel restoration. Kulanihakoi in particular has had so much sediment deposited into its flood plain that this section of the stream is no longer able to rise above its flood banks and access this area of the stream during smaller storm events. Dredging to remove this sediment has been proposed for this stream to restore proper function to the coastal flood plain (Source SMWP 2019). Using the costs cited above, an estimate to restore the entire 2,850 feet of Kulanihakoi makai of the highway would be approximately $690,000 (Source SMWP 2019).
The estuary site is located at the Kaonoulu Estuary and is associated with the outfall of Kulanihakoi Gulch where it meets coastal waters (Source SMWP 2019).
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