Oʻahu Sugar Company constructed the Waiāhole Ditch System to transport, by gravity, water from the northeastern side of the Koʻolau Range. The Waiāhole Ditch collection and delivery system was constructed during 1913-1916.
The general plan or scheme of development adopted for the Waiāhole Water Co. was that recommended by Mr. J. B. Lippincott, C. E., who made an exhaustive study of the project, going fully into the past history and study already made by Mr. J. Jorgensen and other parties, and reported to the Board of Directors of the Oahu Sugar Co., Ltd., under date of August 19, 1911.
The general plan provided for collecting the water from the many streams and gulches on the windward side of Oahu by means of tunnels through the ridges or spurs, and conveying the water, after collecting, through the mountain in the main tunnel to the leeward side of the island, thence by tunnels, ditches and pipes, to the upper levels of Oahu Sugar Plantation.
The tunnels connect up the various streams on the North side, and take in the water at the adits in the gulches. There are 27 of these tunnels on the North side, varying in length from 280 feet to 2,332 feet, the aggregate length of the North side tunnels being 24,621 feet, or 4.66 miles, being in reality one continuous tunnel.
The maximum elevation at which water is taken into the tunnel is 790 feet above sea level, and the grade or slope of the North side tunnels is 1.3 feet per thousand. The length of the main tunnel through the Koʻolau Ridge is 14,567 feet, or 2.76 miles, the grade or slope being 2.0 feet per thousand.
The elevation of the North portal of the main tunnel is 752 feet above sea level, and at the South portal 724 feet. The size of tunnel section is approximately 7 feet wide and 7 feet high, but in many places the section is larger, due to the uneven cleavage of the rock, and the fact that certain portions are unlined.
From the tunnel, the water is then conveyed by means of cement-lined open ditches, elevated concrete ditches, four steel pipes, and three redwood pipes. It is delivered to the upper boundary of Oahu plantation at an elevation of 650 feet through several distributaries, and by the main ditch, which reaches this elevation at the boundary of Honouliuli.
The water is also delivered into numerous reservoirs, especially at night, when irrigating the cane fields is inconvenient. One of the larger reservoirs, on the line of the Waikakalaua storm water ditch, has long been in use. It is called Five Finger Reservoir. Its elevation was a determining factor in establishing the grade elevation of the Waiāhole conduit.
When the work was undertaken, the time of completion was considered an important element, and Mr. Bishop’s organization was planned to secure the most expeditious execution of the project. The General Superintendent of Construction, Mr. Albert Andrew Wilson, who was in direct charge of all the constructing work.
At the beginning of the tunnel work, three shifts of eight hours each were kept going. This was continued until the large amount of water coming into the tunnel, at North heading, became troublesome, and on account of the hardship on the men, working for eight hours in the cold water, it became necessary to cut the shifts down to six hours each, so that four shifts per day were employed for this heading.
The temperature of the water in the tunnel was approximately 66° F., or about 8° colder than the artesian water in Honolulu, or, roughly, about 1° for each 100 feet of elevation.
Camps were established and sanitary conveniences were built to comply with the requirements of the Board of Health. No serious sickness, such as typhoid fever, gave any trouble.
Special tribute should be paid to the Japanese tunnel men, without whom the excellent progress made on the tunnel would have been impossible.
These “professional” tunnel men, as they call themselves, prefer this work to any other, and they apparently take delight in the hardships incident to the work, the exposure to the cold water, and the risk in handling explosives.
They were on the job all the time and never failed to deliver the goods in situations in which white men or native Hawaiians would have been physically impossible. Most of the drilling and mucking was done by these tunnel men as subcontractors – a bonus being given for rapid work, which sharpened their interest and never failed to give results.
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.
These dykes are hard, impervious strata of rock lying approximately at an angle of 45° to the tunnel axis, and nearly vertical, and they occur at intervals of varying length. Between the dykes was the porous water-bearing rock, thoroughly saturated, and with the water pent up between the dykes often under considerable pressure.
When a dyke was penetrated, the water would spout out from the drill holes and would gush forth from the openings blasted in the headings. As the work progressed, the water increased in quantity and the difficulty of the work was enormously greater on account of the water.
The texture and hardness of the rock varied considerably— some of it being particularly soft and porous and much of it hard and flinty—particularly at the dykes. The dykes varied in thickness from 14 feet down to about 4 feet, all composed of very hard, close-grained rock which was apparently waterproof.
From the South portal the progress was rapid, often as high as 630 feet per month, or about 21 feet per day on an average, notwithstanding the long haul, which at the last was over two miles.
Eighty-percent of the length of the main tunnel was driven from the South portal, and 20% of the length was driven from the North portal, the difference in these proportions from the two headings being due to the presence of water at a much earlier stage in the North heading. Had there been no water to contend with, the length driven from each heading would have been approximately the same.
This system of tunnels is essentially a closed-conduit system, that is, the flow is entirely through closed tunnels, not subject to interruption by freshets or washouts or from rubbish or wash from the mountain streams, the intakes being so built as to admit only water as free from rubbish as practicable.
Only at three points in the tunnel system—and these are on the South side, one of which is a gaging station—does the water flow in open channels for an aggregate length of 160 feet.
It is intended to use the reservoirs so far as possible to take care of the water flowing at night, so as to utilize the conduit to its fullest capacity.
The Waiāhole Water Co. has taken over from the Oahu Sugar Co. The water delivered by the Waiāhole System is chiefly used on newly planted cane on land above the lift of the pumps. During construction the water developed in the main tunnel near the South portal was at times utilized for irrigation.
On May 27, 1916, with Mr. H. Olstad as Superintendent, continuous operation of the project was begun. (This post is from portions of a paper read by Chas H Kluegel before the Hawaiian Engineering Association, published in Thrum, 1916)