Wai‘anae Ecological Characterization

Water Resources

Most of the water resources on O‘ahu are a result of the interaction between O‘ahu's high mountains and the high rainfall of the tropics. Moisture from the ocean is driven by the steady trade winds up against the mountains, where it rises, cools, condenses and falls as rain. During normal years, an average of about two billion gallons of rain falls on O‘ahu every day.

This rain soaks into the slopes of the Ko‘olau Range and slowly makes its way down through the porous volcanic rock, ending deep within the basal aquifers (water-bearing rock). It takes an average of about 25 years from the time rain falls on the top of the Ko‘olau mountains to percolate through the rock until it reaches the aquifer and is pumped up through wells into reservoirs and pipelines and into the public water supply system. As rainwater percolates slowly down through the mountains toward the basal aquifers, it is purified naturally by the volcanic rock, producing potable drinking water.

Other water resources on O‘ahu include dike-impounded water, perched groundwater, and perennial and intermittent streams (Shirazi 2004). O‘ahu also uses closed reservoirs to store water for daily community use. Numerous wells, dikes, tunnels, shafts and springs service the island of O‘ahu (Honolulu Board of Water Supply 2004a). O‘ahu has:

• 77 well stations, with 180 potable water wells
• 2 nonpotable wells, at Barbers Point at Lualualei
• 4 shafts (Halawa, Pearl City, Mākaha, and Kalihi)
• 18 tunnels (Honolulu, Windward, and Wai‘anae areas)
• 2 springs (Alewa and Makiki), and 1 nonpotable spring (Kalauao)
• 163 reservoirs (11 in the Wai‘anae District), for a total storage capacity of 169.63 million gallons

Value of Water Resources in Ancient Hawai‘i

The Hawaiians knew the value of their water resources and how to manage them effectively. As populations grew and the demand for food supply increased, the Hawaiians began to make decisions in village-based communities (Juvik and Juvik 1998). By 1100 AD, the Hawaiian culture and their social and economic decisions were dominated by extended family groups (‘ohana) who worked under the leadership of elders (haku) to make resource management decisions, including water resource management. As the village communities grew, their influence spread from the coast to the upland areas, while maintaining the existing ‘ohana and haku leadership. This system evolved into a management system based on ahupua‘a: land units extending from the uplands through the coastal areas, including the reefs and ocean (Derrickson and others 2002).

The ahupua‘a were managed as comprehensive, independent social and economic units, providing a share of seafood, crops, firewood, homesteads, and clothing and construction materials. Hawaiians in the ahupua‘a developed intricate hydraulic systems (‘auwai) for moving water for taro cultivation, and their rules governing water use within the individual ahupua‘a continued to evolve. Many ahupua‘a may not have been independent; the communities traded for items not available in their land, including water resources (Derrickson and others 2002).

The evolution of the ahupua‘a was dependent upon the management of natural resources and water. As a result, the boundaries of the ancient ahupua‘a are very similar to natural watershed boundaries, which are solely dependent upon the flow of water across the land. The ahupua‘a in the Wai‘anae Moku closely follow the natural watershed boundaries of the majestic valleys within the moku. The Wai‘anae Moku consists of nine ahupua‘a:

• Keawaula
• Kahanahāiki
• Mākua
• ‘Ōhikilolo
• Kea‘au
• Mākaha
• Wai‘anae
• Lualualei
• Nānākuli

Most of the streams in the ahupua‘a of the Wai‘anae moku are intermittent at the coastlines, only containing water after large runoff-inducing rain events or during high tides. At higher elevations, streams flow perennially. These perpetually wet areas were once suited to agricultural endeavors in the moku like lo‘i taro cultivation. The stone terraces of these ancient lo‘i are still visible today in the interior valleys of Lualualei, Mākaha, Mākua, and Wai‘anae. Streams that have a hydrologic connection to a groundwater aquifer can be a source of groundwater recharge.

Diversion of Water in the Modern Era

During Wai‘anae’s plantation era, which began around 1880, surface water and groundwater were diverted from the Nānākuli, Kea‘au, and Mākaha Valleys to irrigate sugar fields at the Wai‘anae Plantation (Lao 2002). The millions of gallons of diverted water and a specially created reservoir sustained the plantation, which in turn provided an economic engine for the community for over 70 years. To learn more about Wai‘anae’s agricultural history, please see the Ka Po‘e: Land Management, Agriculture section.

Beginning in the mid-1970s and to the present, water needs for development along Wai‘anae’s coastline have been met by additional well drilling and further diversions of the limited perennial streams. Alteration of streambeds by diversion or concrete paving, or alteration of groundwater resources by pumping, can change stream flow by either reducing the amount of groundwater that enters the stream or by increasing the amount of water that the stream contributes to the aquifer (Oki 2003).

There is increased community interest in understanding water diversions and restoring Wai‘anae’s kalo lo‘i. The Ka‘ala Cultural Learning Center, Wai‘anae High School, and the State Department of Land and Natural Resources (DLNR) are working together to offer opportunities for children, youth, and community groups to get involved in this important work. Several areas in Upper Wai‘anae Valley that were traditionally farmed and inhabited until the early 1900s are being mapped, weeded, and inventoried for their water and cultural resources. Maintaining stream flow is critical to the success of the lo‘i restoration (State of Hawaii DLNR 2004b). Preservation, conservation, and restoration of these resources, in collaboration with the community, reinforces stewardship of the ‘āina and community pride.

The following sections provide information on the surface water and ground water resources of the Wai‘anae moku, as well as information on the modern day threats to these valuable resources and the management programs in place to protect them.

References Cited

Derrickson, S.A.K., M.P. Robotham, S.G. Olive, and C.I. Evensen. 2002. "Watershed management and policy in Hawaii: Coming full circle." Journal of the American Water Resources Association 38(2): 563-577.

Honolulu Board of Water Supply. 2004a. Water for Life Website. http://bws.starrtech.com/cssweb/index.cfm

Juvik, S.P. and J.O. Juvik. 1998. Atlas of Hawaii. University of Hawaii Press.

Lau, C. 2002. Hydrogeology of the Watersheds of Makaha Valley and Waianae Valley. Honolulu Board of Water Supply.

Oki, D.S. 2003. Surface Water in Hawaii: U.S. Geological Survey Fact Sheet 045-03. USGS.

Shirazi, T. 2004. Urban Groundwater Database: Honolulu. International Association of Hydrogeologists. http://www.scar.utoronto.ca/~gwater/IAHCGUA/UGD/honolulu2.html

State of Hawaii Department of Land and Natural Resources (DLNR). 2004b. Sustainability Hotspot: Upper Waianae Valley, Island of Oahu. http://www.hawaii.gov/dlnr/pdf/waianae.pdf

Related References

City and County of Honolulu, Department of Planning and Permitting. 2000. Waianae Sustainable Communities Plan. http://www.honoluludpp.org/Planning/DevSust_Waianae.asp

Hunt, C.D. 1996. Geohydrology of the Island of Oahu, Hawaii. U.S. Geological Survey: Professional Paper 1412-B. U.S. Department of the Interior, USGS. http://hi.water.usgs.gov/pubs/abstracts/pp1412b.html

State of Hawaii Department of Land and Natural Resources (DLNR). 2003. Wao Akua: Sacred Source of Life. Division of Forestry & Wildlife. Honolulu, HI.

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