Ground Water
Traditionally, Hawaiians used perennial streams and springs as their water supply (Juvik and Juvik 1998). Hawaiian society was very dependent on the controlled use of water resources for taro cultivation, and their water transport system (‘auwai) was still in use a century after Captain Cook’s arrival in the Hawaiian Islands in 1778. The use of O‘ahu’s groundwater for potable water supply began in 1879, when a well was drilled on the ‘Ewa plain. This started a new era of developing groundwater resources on O‘ahu.
Potable Water Supply
"Water is going to be a huge problem in Wai‘anae in the future" (Eric Enos, Ka‘ala Farm, personal communication, 2004). Nearly all of the water used for drinking on O‘ahu is derived from groundwater. The Wai‘anae moku is serviced by six wells in Mākaha and three in Kamaile and Wai‘anae (by the Mākaha shaft) and by two tunnels (the Wai‘anae and Plantation tunnels). The Mākaha shaft reaches down to a water collection gallery (chamber) at the surface of the aquifer. The water is pumped from the gallery to the surface for distribution. The two tunnels are used to tap groundwater that is trapped and stored within the underground basalt dikes of the Wai‘anae Mountains.
The region’s total estimated capacity of potable groundwater (including
the Mākaha and Wai‘anae aquifers) is 7.8 million gallons per day
(mgd; City and County of Honolul, Department
of Planning and Permitting 2000). The Commission on Water Resource Management
in 1991 determined in the State Water Resources Protection Plan that the sustainable
yields of the Mākaha and Wai‘anae aquifers are 4 mgd and 3 mgd,
respectively. Sustainable yield can be understood as the estimated amount of
water that can be removed from a resource without adversely affecting the quality
or quantity of the resource.
Groundwater units on the island of O‘ahu.
Source: Commission on Water Resources Management
Communities in the Wai‘anae moku also use potable water from the Pearl
Harbor aquifer to supplement the local supply (City and County of Honolulu,
Department of Planning and Permitting 2000). For the period from 1991 to 1996,
the moku’s 5-year average draw
from the Wai‘anae region’s water sources was 4.5 mgd, and its 5-year
average draw from the Pearl Harbor aquifer was 3.9 mgd. This indicates that
the water needs of the Wai‘anae
moku for that period averaged 8.4 mgd (City and County of Honolulu, Department
of Planning and Permitting 2000). Thus, current water use in the Wai‘anae
community exceeds the sustainable yield of potable water sources within the
moku (7.8 mgd). The Honolulu Board of Water Supply has proposed the construction
of two additional storage tanks in Nānākuli and Mākaha, with
a total capacity of 4 million gallons. The Board of Water Supply’s policy
is that storage capacity for a district should be one-and-a-half times the
average daily demand. Construction of these storage tanks will help ensure
a safe temporary supply of water for the moku in the event of an interruption
of the regular service or for use during peak demand periods.
The Board of Water Supply’s 2004 Consumer Confidence Report found that concentrations of regulated contaminants in the wells and shafts that service the Wai‘anae moku are below the Maximum Contaminant Levels (MCL) set by the U.S. Environmental Protection Agency for safe drinking water. The regulated contaminant detected at the highest concentrations was 1,2,3-trichloropropane. It was found in Ho‘āeae Wells and Kunia Wells, which are sources of water for some parts of the moku, at a maximum concentration of 0.600 micrograms per liter, which is equivalent to the MCL. 1,2,3-trichloropropane is often used to make other chemicals and is an ingredient in industrial solvents, paint and varnish remover, and cleaning and degreasing agents (Honolulu Board of Water Supply 2004a).
Nonpotable Water Supply
Nonpotable water is water not suitable for drinking purposes and is generally used for fire control and agricultural and landscape irrigation. The major source of nonpotable water on O‘ahu is treated wastewater. This reclaimed water makes efficient use of limited water resources. The most common use of nonpotable water is for agricultural irrigation.
Reclaimed water is not currently available for use in the Wai‘anae moku.
A decrease in demand from the agriculture industry in ‘Ewa and Central
O‘ahu has increased the supply of nonpotable water that could potentially
be available to farmers of the Wai‘anae moku. Unfortunately, the high
cost of installing nonpotable irrigation service to a small farm in Wai‘anae
can be prohibitive. There is also an "impact charge," a
fee charged to new agricultural users for initial hookup to the water supply,
that drives up the cost of agricultural water use, as do new environmental
laws that affect construction (City and County of Honolulu, Department of Planning
and Permitting 2000).
Meeting Wai‘anae’s Water Needs in the Future
The Honolulu Board of Water Supply has estimated that the water needs of
the Wai‘anae moku will approach 12.3 mgd by 2020. Although the sustainable
yield in the moku is estimated at 7.8 mgd, the average pumping rate in the
mid to late 1990s was only 4.5 mgd. If pumping of water sources in the moku
were to continue at that rate, almost 8 mgd would have to be brought from the
Pearl Harbor aquifer or another source to meet Wai‘anae’s projected
needs for 2020 (City and County of Honolulu, Department of Planning and Permitting
2000).
As populations continue to increase island-wide, the overall quality of the groundwater can potentially decrease. Sustainable yield is an estimated value based on large-scale calculations. As the amount of water that is extracted from an aquifer approaches the sustainable yield, the likelihood of exceeding the sustainable yield increases. Draining aquifers too deeply can disrupt the balance of the freshwater lens of the aquifer, causing saltwater contamination of the freshwater supply.
Spatial relationship between fresh and salt groundwater.
Source: Commission on Water Resources Management
To prevent this outcome, the Board of Water Supply plans to implement an aquifer monitoring program by constructing deep monitoring wells in critical aquifers around O‘ahu. By taking measurements of the freshwater-saltwater transition zone, the Board of Water Supply can more accurately monitor the aquifers' response to extended use. The measurements will help determine if an aquifer’s thickness is shrinking due to overpumping, before water quality is affected (Lanzilotti 2003).
Kalo Culture, Tapping into the Roots of Hawai‘i's Life-Giving Ancestral Plant
"One cannot talk about growing taro without talking about water rights, an issue that has posed serious challenges for the farm [Ka‘ala Farm], and for contemporary taro growers in general." Over the last century, large amounts of Hawai‘i's surface water has been diverted away from natural streams and traditional taro areas to support sugar plantations and other modern commercial uses. The effect, Enos says, has been to contribute to "the whole breakdown of Hawaiians' connection to the land and fishing and everything else."
'The [Wai‘anae] valley got dried out to make a town," says Butch DeTroye, Ka‘ala Farm's facilities manager. "But we believe it's possible to put the water back, and share it with the forests, too." Enos says he went through years of bureaucratic struggles to bring water from a diversion ditch down to the valley, where it used to run. "We still don't have enough water," he says. "But I think we're closer to the driver's seat. Before, we weren't even in the bus."
– An article by Leslie Lang, Hana Hou Magazine
Population increases lead to increased land development. Urbanization and changes in land use can also affect water supplies. Agricultural runoff, long-term pesticide use, improper hazardous waste storage, and reduction of vegetated acreage all can adversely affect water quality. Though water seems plentiful on O‘ahu, misuse of the island’s water resources can exhaust the supply. Each individual has an impact on the delicate balance of the Wai‘anae watersheds. Maintaining high-quality water in the moku demands conservation, education, and responsible use.
References Cited
City and County of Honolulu, Department of Planning and Permitting. 2000.
Waianae Sustainable Communities Plan. http://www.honoluludpp.org/Planning/DevSust_Waianae.asp
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.
Lanzilotti, S.S. 2003. WHO-KOBE Report: Water Quality. City and County of
Honolulu. Department of Emergency Services. http://www.co.honolulu.hi.us/esd/reportc.htm
Related References
Lang, L. 2002. "Kalo Culture: Tapping into the Roots of Hawaii's Life-Giving
Ancestral Plant." Hana Hou! The Magazine of Hawaiian Airlines 5(1).
Lau, C. 2002. Hydrogeology of the Watersheds of Makaha Valley and Waianae
Valley. Honolulu Board of Water Supply.
State of Hawaii Department of Land and Natural Resources (DLNR). 2004a. Commission
on Water Resources Management. http://www.hawaii.gov/dlnr/cwrm
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