Kam 1 Clean-Up: conceptual design update

Kamaole Beach Park I · Kamaole Ahupuaa · November 2026

What this update adds

The Kam 1 pilot now has a design sized to the water that actually arrives. Three maps replace the earlier sketches: the Kamaole Gulch watershed with its 100-year flows marked at every bottleneck, a terminal site plan for the beach park, and a chart that sets the runoff loads against the storage the design provides.

The Kamaole Gulch watershed above Kam 1 with numbered culvert and bridge bottlenecks and the outfall at K — The Kamaole Gulch watershed above Kam 1. Numbered markers are the four culvert and bridge bottlenecks between Piʻilani Highway and the beach; K is the outfall. Flows are the County's 100-year values.

The watershed behind the beach

Kamaole Gulch drains 3,333 acres to the sand at Kam 1. In the 100-year storm, 2,871 to 3,765 cubic feet per second arrives at the beach, against culverts that pass 550.

Piʻilani Highway: two 96-inch culverts built for 979 cfs, facing a 2,806 cfs design flow.
Kanakanui Road and Kuli Puu Street: the flow is still above 2,800 cfs through both Conspan crossings.
South Kihei Road: one 11'-5" by 7'-1" arch pipe passing 550 cfs against 2,871 cfs. In past storms, the County records, the lawn of this park was completely washed away.

What the stream actually carries

The gage record tells a different story from the design storm, and the design has to answer both. USGS station 16663500 measured Kamaole Gulch from 1980 to 1997. Most years the channel recorded no flow at all. Its peaks were 291 cfs on March 17, 1982, 207 cfs on January 10, 1980, 70 cfs on January 20, 1997 and 50 cfs on December 6, 1988. A dry gulch that occasionally becomes a river, not a stream with a steady load. That is why the configuration is built in tiers rather than around a single design storm.

Terminal site plan at the Kam 1 outfall showing the forebay, biofiltration basin, vegetated swale, dune and sand bypass, and the South Kihei Road crossing — Terminal configuration at the outfall. One is the forebay, two the biofiltration basin, three the vegetated swale, four the dune and sand bypass, five the South Kihei Road crossing, K the outfall.

The basin configuration

Three cells at the beach, two basins upstream, each matched to a load regime.

Facility	Size	Storage	Function
1Sedimentation forebay	70 × 45 ft, 3 ft deep	0.22 ac-ft	Traps bed load and the sand that reaches the park
2Biofiltration basin	105 × 72 ft, 2.5 ft ponding	0.43 ac-ft	Amended soil, 48 in media, underdrain, 60 cfs treatment flow
3Vegetated swale	300 ft, 12-ft bottom	0.14 ac-ft	Carries treated flow to the dune without a concrete channel
4Dune and sand bypass	100 ft at the mouth	n/a	Keeps the beach face in balance
5Basin A, Piʻilani Basin 21	regional detention	15 ac-ft	Shaves the flood peak before it reaches the highway
6Basin B, mid-slope	detention	4 ac-ft	Second stage of peak shaving and sediment capture

Matched to the loads

Load case	What arrives	What the system does
Routine storms	up to about 70 cfs, the range of the gaged record	Whole train in series; all flow treated
Moderate events	up to about 290 cfs, the 1982 peak	Forebay and swale treat, biofiltration partially bypasses, dune takes the rest
Flood	2,871 to 3,765 cfs, 100-year	Energy dissipation at the outfall, dune and floodplain absorb it, no lawn loss

Chart comparing incoming runoff loads against culvert capacity and storage provided against the water-quality volume — Left, what arrives against what the culverts pass. Right, storage provided against the water-quality volume of the makai basins.

The honest arithmetic

The beach end can hold about one acre-foot of live storage in total. The first flush of just the makai basins, half an inch over 249 acres, is 10.4 acre-feet. The whole watershed's first flush is 139 acre-feet. A beach park cannot hold either number. So the configuration splits the job: the beach treats the routine storms that carry most of the sediment and bacteria to the water, and the storage that changes the flood peak belongs upstream, in Basins A and B and in the retention any new development mauka of Piʻilani Highway should have to build before it builds houses.

Build order

Forebay, swale and dune work (volunteer scale, light permits, one dry season).
Biofiltration basin (engineered and permitted, about a year).
Basins A and B (capital scale, tied to County drainage improvements or a development agreement).

How we will know it works

A staff gauge and sediment depth markers in the forebay, four fixed photo points, water sampling after the first storms of each season, and an annual report to the community with the numbers in it.

Caveats

This is a conceptual design, not a set of engineered drawings. Footprints are indicative, sized from public elevation data and the County's published flows. A field survey, geotechnical work and hydraulic modelling come next, followed by County and State permits, including any conservation district or Army Corps review that applies at the beach. The flows quoted are the County's and FEMA's, not ours.

Source documents

Kamaole Ahupuaa Drainage Report (November 6, 2026).
Liilioholo and Kaluaihākōkō name history report (November 7, 2026).
County of Maui Kīhei Drainage Master Plan, R.M. Towill, November 2016, sections 4.6 and 4.7.
FEMA Flood Insurance Study, Maui County, 2005.
USGS station 16663500 peak-flow records 1980-1997.

Join the clean-up

The full drainage report and maps are available on request at social@kamaoleliving.com.