Before construction of the Waiahole ditch system, the stretch of the Ko`olau mountain range from Kahana to Waiahole could be thought of as an enormous reservoir. Water entered the mountains when rain, released from clouds snagged by the mountain peaks, soaked into the ground or when condensation collected on trees dripped into the soil. A vast, complex web of dense basaltic dikes trapped up to 50 billion gallons of water in porous volcanic rock in the mountains’ interior spaces.
When heavy rains fell, the spillage over the tops of the dikes would tumble out as waterfalls down the face of the mountains. Otherwise, the water would find its way out of the dikes through springs and seeps that fed the windward streams or through drainage into the low-lying basal aquifer.
The Waiahole ditch system changed all that. Of the 50 billion gallons that hydrologists believe was stored in the Ko`olaus before 1912, 92 percent — or 46 billion gallons — was drained off during the years of construction and immediately following. High-level springs in the back of Waiahole Valley that in 1911 were measured as having a total of nearly 6 million gallons a day dried up following completion of the main tunnel bore. Flows in Waiahole Stream, which in extremely dry years still had up to 15 million gallons a day average flow — and up to twice that in rainy years — were reduced by the Waiahole ditch construction to half that, or about 8 million gallons a day, in the wettest of times.
Still, people who lived in Waiahole Valley in the 1940s, 1950s and early 1960s recall greater flows back then than exist today. Several of them provided testimony during the contested case hearing, saying that in their youth, they recalled the streams having sufficient water to allow swimming and bathing, abundant fishing, and greater acreage in wetland taro cultivation. Most of the people interviewed by Davianna McGregor, a professor of American Studies at the University of Hawai`i who testified for the windward parties, agreed that the most noticeable decline in stream flows and stream resources occurred starting around 1962.
McGregor said her informants reported that up through World War II, “Waiahole, Waikane, and Haikpu`i — each had clean, cold, year-round swiftly flowing streams abundant with native stream life… Informants from Waiahole, Waikane, Hakipu`u and Kahana who are in their fifties and sixties recall that in their youth, the native stream life was abundant and included two species of `opae [shrimp] … different species of o`opu, including the o`opu nakea, some hihiwai, gold and red swordtails, kuna the freshwater eel, catfish, and frogs.
“The o`opu were large and abundant. A good-sized o`opu would be six to eight inches and real big ones were ten to eleven inches long….
“There were several deep pools in the stream, such as by the poi factory… Aholehole went up as far as the fork in the stream where it becomes Waianu and Halona. You could easily hook 30 aholehole in one day…
“Apparently, the impacts of the diversion on the river flow were gradual, almost imperceptible, seemingly natural but nevertheless steady and cumulative. Informants noticed changes at different points in their lives. However, all agree that the most noticeable decline in water and in natural resources occurred after 1962 to 1963. After that, the aquatic and terrestrial natural resources declined in amount and in size.”
The testimony of McGregor and others opened the door for the leeward parties to argue that factors other than construction of the ditch half a century earlier had nothing to do with what is now a lack of water in the streams. Yet, according to a chart showing flows in the ditch from 1916 to the present, there was sharp increase, up to 5 million gallons a day, starting in the late 1940s, and attributable generally to the digging of blind development tunnels, particularly the Uwau tunnel. When the Uwau tunnel was extended in 1963, flows in the ditch jumped again, gaining nearly 3 million gallons a day.
Not only is water above the level of the tunnels drained out, but the water pressure below the tunnels is lower. Since it is the build-up of pressure that causes water to emerge from springs and seeps, the tunnels thus have not only a devastating impact on flows above the elevation of the tunnels, but also, as hydrologists K.J. Takasaki and John F. Mink have written in a U.S. Geological Survey bulletin, a potentially significant effect on stream flows below the tunnel elevation.
William Meyer, of the U.S.G.S., testified that the flow gained by the ditch when the Uwau tunnel was extended amounted to “a high percentage” — between a third and a half — of the total baseflow in the streams at the time. A reduction of that magnitude, he said, would certainly be apparent to the naked eye.
In recognition of the loss of the storage capacity of the mountains that occurred as a result of the tunnels breaching the dikes, several efforts have been made to plug a handful of dikes by construction of bulkheads in the tunnels. The earliest experiments were made by Waiahole Irrigation Company in the 1930s. Neither bulkhead worked, however, and both were eventually removed.
In 1955, the City and County of Honolulu developed a bulkhead at the back of a tunnel in Waihe`e Valley. That appears to have been the first successful effort at bulkheading.
Beginning in the late 1980s, the state Department of Land and Natural Resources began planning for development of two bulkheads in Kahana tunnel, a part of the Waiahole Ditch system. Work on the project was completed in 1994, at a reported cost of $1.6 million. At last report, water pressure appears to be building up behind the bulkheads, but, according to an engineer for the state Division of Water and Land Development, it will be years before the water behind them rises to its pre-tunnel pressures.
Because the dike system was so thoroughly disturbed by the ditch system, and because the windward streams in their pre-ditch state were literally the expression of that dike system, it is probably impossible now or at any time in the future to reconstruct “natural” flows of water in the stream channels. Rather, what has been done since December 1994 has been to release daily millions of gallons of water from the Waiahole ditch into the Waiahole Stream channel. This has created a reach of fast-flowing current in Waiahole Stream that almost certainly did not exist in pre-ditch times. Witnesses for leeward parties testified that this was likely to result in erosion and loss of habitat for some native species, including o`opu and damselflies.
Still, the benefits of restored flows in downstream reaches of Waiahole Stream have been, since 1994, dramatic and positive, to judge from the statements of many witnesses who testified during the contested case hearing. What the Water Commission must decide is whether stream restoration must await a time when it can be “natural” — that is, after thousands of dikes breached by the tunnel system are bulkheaded, at a cost probably approaching the gross state product for decades to come — or whether the restoration must begin now, under conditions that at some places, will inevitably diverge from the natural.
(For further reading, please see the article, “[url=/members_archives/archives_more.php?id=1302_0_30_0_C]Fingers in the Dikes: State Tries to Plug Flow from Kahana Tunnel[/url],” in the September 1994 edition of Environment Hawai`i. A short bibliography appears at the end of that article.)
Volume 7, Number 3 September 1996
Leave a Reply