Two intermittent streams bisect the SEIS Lands; O‘io near the center of the property, and Kawela near the western end of the property. On the makai side of Kamehameha Highway storm water runoff flows into the following four major drainage channels and into Punaho‘olapa Marsh.
- Kawela Stream is an unlined open channel with its opening to Kawela Bay. It is estimated that the stream conveys storm runoff from about 771 acres mauka of Kamehameha Highway into Kawela Bay and 13 acres of the lands addressed in the supplemental environmental impact study (SEIS).
- The West Main Drain is also an unlined open channel. Its terminus at Turtle Bay consists of two 48-inch concrete pipe culverts. As originally designed, it conveys storm runoff from about 193 acres of land mauka of Kamehameha Highway and about 37 acres of land within the SEIS Lands.
- The West Kuilima Drain consists of two 72-inch diameter pipe culverts near the shoreline. It conveys storm runoff generated from about 72 acres within the SEIS Lands.
- The East Main Drain is a trapezoidal unlined open channel that passes through the Fazio Golf Course and terminates at Kuilima Bay. The terminus consists of a concrete and rubble masonry structure with four 72-inch concrete pipe culverts. It conveys storm runoff from approximately 1,664 acres of mountainous land mauka of Kamehameha Highway and 60 acres of the SEIS Lands makai of the highway.
Punaho‘olapa Marsh is a wetland located in the eastern portion of the SEIS Lands. It receives runoff from approximately 306 acres within the SEIS Lands, of which approximately 96 acres make up the marsh. It also receives runoff from 430 acres mauka of Kamehameha Highway. Most of the water within the marsh percolates into the ground with some overflow during major storms conveyed to the East Main Drain by a small ditch. During larger storm events the marsh overflows onto the golf course.
The City and County of Honolulu previously approved a drainage master plan for the SEIS Lands. The Resort Master Plan includes the following drainage improvements recommended in the approved drainage plan:
- Re-contour the golf course fairways to widen the drain channels.
- Widen East Main Drain to become a grass-lined channel. Also, replace the existing 72-inch drain culverts with a rip-rap lined outfall channel.
- Widen the grass lined Punaho‘olapa Marsh Ditch.
- Widen West Main Drain to become a grass-lined channel. Replace the existing 48-inch drain line outlets to the ocean with a rip-rap lined outfall channel.
In addition to the above, as part of its plan, Turtle Bay Resort is reviewing the construction of approximately 30 acres of storm water retention and detention basins in the agricultural area mauka of Kamehameha Highway. These basins would be intended to intercept storm water runoff during heavy rainfall events and reduce flooding across Kamehameha Highway and into the SEIS Lands.
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The plan also includes upgrading the wastewater treatment plant from R2 to R1 treatment level that will enable the use of reclaimed water in the vicinity of residences.
Turtle Bay Resort is the owner of the Opana Wells mauka of Kamehameha Highway. Two of these wells have been improved and are expected to be transferred to the Board of Water Supply (BWS) in 2011. The third well has been tested, but not yet improved. The total capacity of the two wells being transferred to the BWS is 2 mgd. The estimated capacity of the undeveloped third well is 1 mgd.
The total drinkable water average daily demand for the Resort Master Plan is estimated to be 0.72 mgd with maximum demand estimated to be 1.08 mgd. The Opana Well system will be the source of drinkable water.
The existing sources of irrigation water along with additional reclaimed water from the resort’s treatment plant are considered adequate to address the demand resulting from the Resort Master Plan.
Water conservation measures are employed at the resort to conserve water and this strategy will continue as the Resort Master Plan is implemented. The continued use of reclaimed water from the resort’s treatment plant mitigates the impacts of additional landscaping requirements associated with the Resort Master Plan.
Rerouting runoff in Kawela Stream to the West Main Drain will have a significant beneficial impact upon water quality in Kawela Bay. This rerouting will help to mitigate the significant adverse impacts of regional drainage that are not attributable to the Resort Master Plan. The Draft SEIS will present in greater detail any additional mitigation measures that may be necessary.
Storm water drainage and runoff from manmade structures within the SEIS Lands are required by law to be retained on site, such that there is no net increase in storm water runoff from the property. No significant adverse drainage impacts are anticipated to result from implementation of the Resort Master Plan because all development is required to comply with the standards established by the federal government, the State Department of Health, and the City and County. Nevertheless, the possibility of such impacts will be studied and addressed in the Draft SEIS.