The Ko`olau range is one of two extinct volcanoes that make up the island of O`ahu. Most of the rock in the Ko`olau mountains is porous — a`a and pahoehoe lava flows, volcanic clinkers and breccia — but throughout much of the range, a series of dense, basaltic dikes lace the mountains’ interior, creating near-impermeable impoundments. When the heavens open and the rains fall, the interstices of the porous rock fill with water, giving the mountains the aspect of a mammoth, natural reservoir.
Until the twentieth century, the water in the rock was in an equilibrium with the springs, streams, and lower-level bodies of water, including the freshwater basal lens and the sea. Water was released into springs when the water table was high enough to reach the upper elevations of the dikes. Streams were fed as their beds cut through the dikes holding back the water. From the bottom of the dike system, which could extend below sea level, water flowed into the basal lens or, in the case of dike impoundments near the coast, into the sea.
Altogether, some 560 billion gallons of water are estimated to have been held above sea level in the 135-square mile area extending from Waiale`e, near Kawela Bay, south to Waimanalo.1
The Dams Break
The earliest water-development tunnel in the Ko`olau range was dug in 1888, near Waimanalo. Just 125 feet long, it was apparently successful enough to encourage further efforts. In 1893, a 449-foot-long tunnel at the back of Maunawili Valley turned out to be dry. A second Maunawili tunnel, 350 feet long, was dug around 1900. That yielded water for irrigation.2
But what turned out eventually to be the most successful network of water-development tunnels in the Ko`olau was originally intended to be a water-transmission tunnel.
About 1904, engineers hired by O`ahu Sugar Company began designing a plan to bore all the way through the Ko`olau range. Water collected from streams and springs on the wet windward coast, from Kahana to Waiahole, would be channeled into a series of ditches and short tunnels running along the face of the cliffs just below the 800-foot contour. At the back of Waikane Valley, the water would enter a nearly 15,000-foot-long tunnel leading under the Ko`olau crest and emerging on the leeward side. From there, the water would travel through a series of siphons and pipes, ultimately to be shunted onto the cane fields of the O`ahu Sugar plantation.
In 1913, a crew of Japanese tunnelers began boring into the mountain at the back of Waiahole Valley. Accounts of the work indicate that the quantity of water encountered when the first dikes were breached took engineers by surprise.
In a paper delivered in 1917 to the Hawaiian Engineering Association, Charles H. Kluegel described what he called “interference by water:”
“While it was suspected at the outset that considerable water might be encountered in the main bore through the mountain, it was not anticipated at the beginning that enough water would be developed to materially interfere with the progress of the excavation. This hope was not realized, however, for the main bore had proceeded only about 200 feet from the North portal when water to the extent of two million gallons daily was developed — this on breaking through the first dyke.”3
More Straws in the Glass
Within a few years, what to Kluegel had been an impediment was being described by geologist W.O. Clark as a bonanza. In 1922, Clark described to C. Brewer & Co. the advantages of tapping dike-confined water. As described by Takasaki and Mink, “Clark was the first to recognize the balance that exists between natural recharge and discharge in a ground-water reservoir formed by dikes. Although it was recognized early that a tunnel has its largest flow when newly dug and that this flow will diminish to some lower rate, it was Clark who first attributed this to depletion in reservoir storage. He explained that the quantity of water obtained initially by tunneling depends on the position at which the reservoir is tapped; also, that it is possible to tap the reservoir to such an extent that it will be completely drained and, thereafter, will not behave as a reservoir at all in that the yield will fluctuate with climatic conditions.”4
Starting in 1925, the Waiahole Water Company, owned wholly by O`ahu Sugar, began work on blind tunnels bored into the Ko`olau specifically for the purpose of water development, as described by Clark. Between 1925 and 1935, six development tunnels were dug, and four of them hugely successful (Kahana, Waikane 1, Waikane 2, and Uwau). The water gained from them was added to the total flow in the Waiahole ditch.
Running on Empty
The high initial flow of water in the tunnels was not sustainable, since most of it had been water dammed up by the dikes and released quickly when the dikes were punctured. According to Takasaki and Mink, of the 50 billion gallons of stored water drained by all windward tunnels, 46.2 billion was drained through the Waiahole ditch system. Minor withdrawals can be attributed to tunnels bored by other plantations and the Honolulu Board of Water Supply.
But draining the mountains — or at least that part of the mountains above the elevation of the tunnels — was not without long-term consequences.
The pre-existing equilibrium between dike-impounded water and windward streams and springs originating high in the mountains was forever altered when the elevation of the water table in the impoundments was lowered. For example, two springs in Waiahole Valley that emerged from the mountains about 750 feet above sea level were measured in June 1911 as having a total flow of 5.7 million gallons a day. When the main bore of the Waiahole tunnel was dug, the springs dried up.5
Estimates vary of the amount of water lost from the Waiahole watershed to the tunnel. However, in 1947, W.E. Armstrong, hydraulic engineer for the U.S.G.S., prepared a short report for the territorial commissioner of public lands that seems to be as dispassionate and accurate as any available.6 Armstrong estimated that average flows in Waiahole Stream before 1912 were around 15.2 million gallons a day and after the tunnel was completed, about 8.2 mgd. On the basis of flows recorded by Waiahole Water Company, Armstrong then calculated that about 7 million gallons a day was contributed as the tunnel passed through territorial land at the back of Waiahole Valley. “Although records are scanty,” Armstrong concluded, “they seem to indicate that there was a yearly average of about 15 million gallons a day available before the tunnel was built and 8.2 million gallons a day under existing conditions.”
Turning reservoirs into funnels had drawbacks for the leeward users as well. No longer could the mountains be counted on to provide a store of water that could be drawn down in dry spells. Rather, water in the tunnel increased and diminished practically in lockstep with mountain rainfall (albeit with a certain time lag).
Plugging the Dikes
By 1934, most of the stored water had been drained from the impoundments breached by the Waiahole tunnel system. In hopes of re-establishing the ability of the mountains to hold water, W.O. Clark recommended placing a bulkhead in the Waikane 2 tunnel. Eventually, both Waikane 2 and Uwau tunnels received bulkheads.
The early experiments did not work because, as Takasaki and Mink report, the bulkheads were too close to the portals and too distant to the back of the tunnels, where the main storage area exists. Eventually, both bulkheads were removed.
A bulkhead that the Board of Water Supply placed in 1955 at the back of its tunnel at Waihe`e, however, has been “spectacularly successful,” Takasaki and Mink report.7
In their work, published in 1985, Mink and Takasaki acknowledged that “the vast initial storage that has been depleted could not likely be returned to its original state because of disruption to the integrity of the reservoir caused by tunnel construction.” Significant portions of it, however, “can be restored and manipulated economically in each of the development tunnels in a manner similar to that employed in Waihe`e tunnel. Correctly located and properly built bulkheads in the tunnels could provide the means for improved management of the water resource.” The best candidate for bulkheading in the Waiahole system, they concluded, was the Kahana tunnel. At its head (that is, at its farthest point in the mountain), “access to more than 10 billion gallons of principal storage was attained” by the tunnel, with the “optimal location for a bulkhead” being somewhere “in the final 300 feet of the tunnel.”8
Plugging Away
In 1985, the state Legislature appropriated $90,000 in the fiscal year 1985-86 budget for the design and planning of the “Waiahole Ditch Bulkheading Project.” (The justification sheet attached to the budget, and completed by the Division of Water and Land Development of the Department of Land and Natural Resources, identified the “individuals or organizations” having an interest in the project as the Honolulu Board of Water Supply, the Hawai`i Housing Authority, and “land developers in the leeward areas.”)9
In 1993, the two bulkheads at the back of Kahana tunnel were in place. Just this summer, in July, the bugs were finally worked out of a remote control system that allows valves in the bulkheads to be controlled from offices at the DLNR building in downtown Honolulu. A computer hooked up to gages allows for constant monitoring of the pressure building up behind the bulkheads.
The Kahana tunnel was built by the Waiahole Water Company and is still a part of the system owned by Amfac. According to the environmental assessment prepared for the project (1990), the purpose of the bulkheading project is “to improve water service to users of the Waiahole transmission system.” The users are not further identified. In the “Summary and Recommendations” of the EA, one of the listed benefits of the project is that it will “provide management with a means to regulate flows under varying degrees of demand.” Again, no identification of “management” is provided.
Whose Water Is It?
From the outset, though, documents at the Division of Water and Land Development show Amfac was involved from the earliest stages of project planning. The original intent appears to have been for the state and Amfac’s O`ahu Sugar to reach an agreement as to the operation of the valves in the bulkhead.
In 1990, negotiations on a draft agreement were still ongoing. By letter dated June 22, 1990, Manabu Tagomori, DOWALD administrator, responded to concerns raised by W.D. Balfour, Jr., vice president and manager of O`ahu Sugar: “We have no objections to the operation and management of the bulkhead system by O`ahu Sugar Company. We will revise the project plans to provide for the remote monitoring of flows and pressures of the bulkhead system from both of our offices (OSCo and DOWALD)…
“The project is a joint undertaking by OSCo and the state with OSCo contributing the use of the aqueduct system and is [sic] responsible to provide the personnel to operate and maintain the bulkhead system and the state is responsible for its construction and repair. Therefore, the rental rate of the aqueduct system shall not be increased to recover the construction nor maintenance costs of the bulkhead system when the lease is required to be renegotiated.”
Efforts to arrive at a memorandum of understanding continued through 1992, but appear to have borne no fruit. By 1993, to judge from DOWALD files made available to Environment Hawai`i, neither Amfac nor the DLNR was attempting to revive the negotiations. With both hardware and software now in place, DOWALD has its finger — and its alone — on the button to control the release valves.
Research Perforce
Elsewhere and at other times, the research benefits of the project have been cited to justify the bulkheads. In fact, in a June 25, 1990, letter to Balfour, then-Land Board Chairman William Paty attempted to dispel Balfour’s suspicions that the state or city had designs on the stored water by noting the high-minded aspects of the project: “Contrary to statements that the project is being developed for domestic purposes, we at the Department restate that the project is intended to prove out the technology of restoring dike-confined waters with the idea of transferring this method once proven to other facilities throughout the state.”
With the phase-out of O`ahu Sugar, it would appear as though the project will be able to be used to support research efforts. Since the bulkheads have been put in place, water pressure behind them has been building slowly, indicating that the dikes punctured seventy years ago have once more begun holding back water. As of July 21, 1994, pressure readings of 21 pounds per square inch were obtained behind the outer bulkhead, equivalent to a column of water 49 feet high. Behind the inner one, the pressure was 18 pounds per square inch, equivalent to a water column 42 feet high. By contrast, Stearns and Vaksvik report that when the first dike was encountered in drilling from the south face of the main transmission tunnel, hydraulic pressured of 67 pounds per square inch “indicated that water was standing in the rocks at least 150 feet above the tunnel, or 900 feet above sea level.”10
According to a status report dated March 24, 1994, by Pericles Manthos, the DOWALD engineer working most closely on the project, “pressure increases noted from last October to the present are probably indicative of an actual storage capacity increase behind the bulkheads. The key factor in determining the relative capacity of this reservoir will be dependent on long-term testing and may take several months to quantify. The testing recently completed has been very positive in that it has shown a substantial recovery factor exists.”
No water has been released since the bulkheads were installed. But it will take years — decades, at least — before water levels behind the bulkheads build back to their pre-tunnel levels and are high enough to feed once more the springs and streams of windward O`ahu.
* * *
For Further Reading
“The Waiahole Tunnel Project,” no author, in Thrum’s Hawaiian Annual, 1916, pages 174-180.
“Engineering Features of the Water Project of the Waiahole Water Company,” by Charles H. Kluegel, Thrum’s Hawaiian Annual, 1917, pages 94-107.
“Geology and Ground-Water Resources of the Island of O`ahu, Hawai`i,” by Harold T. Stearns and Knute N. Vaksvik, Bulletin 1, Division of Hydrography, Territory of Hawai`i (May 1935).
“Water Resources of Windward O`ahu,” by K.J. Takasaki, G.T. Hirashima, an E.R. Lubke, U.S.G.S. Water Supply Paper No. 1894 (1969).
“Evaluation of Major Dike-Impounded Ground-Water Reservoirs, Island of O`ahu,” by K.J. Takasaki and J.F. Mink, U.S.G.S. Water Supply Paper No. 2217.
1 For an exhaustive description of the topic of dike-impounded water, see K.J. Takasaki and J.F. Mink, “Evaluation of Major Dike-Impounded Ground-Water Reservoirs, Island of O`ahu,” U.S.G.S. Water-Supply Paper No. 2217 (1985), prepared in cooperation with the Board of Water Supply, City and County of Honolulu.
2 See Takasaki and Mink, page 21.
3 Reprinted in Thrum’s Hawaiian Annual, 1917.
4 Takasaki and Mink, p. 3.
5 Harold T. Stearns and Knute N. Vaksvik, “Geology and Ground-Water Resources of the Island of O`ahu, Hawai`i,” Bulletin 1, Division of Hydrography, Territory of Hawai`i (May 1935), page 403.
6 “Analysis of Published Geological Survey Stream Gaging Data for Waiahole Drainage Area on Territorial Lands as Compared with Other Long Time Stream Flow Records on O`ahu,” report to A. Lester Marks, Commissioner on Public Lands & Survey, January 27, 1947.
7 Takasaki and Mink, p. 35.
8 Takasaki and Mink, p. 32, 35.
9 The contract for design, development of construction plans and specifications, preparation of an environmental assessment, cost estimates, etc., was awarded to George A.L. Yuen & Associates, which later became Mink & Yuen, Inc. The first contract called for payment of just over $82,000. Three addenda to the contract more than doubled the cost of the work to $185,950. The Division of Water and Land Development has stated publicly that the total cost of the bulkhead project, involving placement of two bulkheads, is about $1.6 million.
10 Stearns and Vaksvik, pages 400-401.
Volume 5, Number 3 September 1994
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