November 2000: A storm moving in from the Eastern Pacific in late October has left the eastern slopes of Mauna Kea and Mauna Loa waterlogged from the tree line down to the coast. By November 1, when a second storm socks the windward coast of Hawai`i Island, the porous volcanic soils can absorb no more. At the Hilo airport at sea level, nearly 28 inches of rain cascade from the heavens in one 24-hour period. In more inland areas, rainfall is heavier yet.
Flooded streams gouge their banks and eat at the foundations of homes built alongside them. Channels designed to contain 100-year-floods are tested, and more than one fails. Bridges collapse. Roads wash away. The soccer fields along the front of Hilo Bay are turned into a boulder-strewn wasteland. Downtown businesses flood and houses from sea level to miles inland are evacuated. Yet no lives are lost and such injuries as occur are minor.
More than a year later, Hilo is still trying to recover from the heaviest rainfall in its history and one of the worst floods anyone can remember.
‘Quick quick, or the waters will stop you’
The Reverend Titus Coan, a missionary to Hawai`i in the second half of the 19th century, described his experiences with the Hilo floods in this excerpt from his book, Life in Hawai`i:
The streams were the most formidable obstacles. In great rains, which often occurred on my tours, when the winds rolled in the heavy clouds from the sea and massed them in dark banks on the side of the mountain, the waters would fall in torrents at the head of the streams and along their channels, and the rush and the roar as the floods came down were like the thunder of an army charging upon the foe.
I have sometimes sat on the high bank of a streamlet, not more than fifteen to twenty feet wide, conversing with natives in the bright sunshine, when suddenly a portentous roaring, like the sound of many waters, or like the noise of the sea when the waves thereof roar, fell upon my ears, and looking upstream, I have seen a column of turbid waters six feet deep coming down like the flood from a broken milldam. The natives would say to me, ‘Awiwi! Awiwi! O pea o`e I ka wai’ – “Quick quick, or the waters will stop you.”
The full text is available on the web at [url=http://www.revival-library.org/catalogues/world3/coan-lifeinhawaii/03.ihtml]http://www.revival-library.org/catalogues/world3/coan-lifeinhawaii/03.ihtml[/url]
Federal Bail-Outs
When the skies cleared, the damage assessments began. The bayfront soccer fields were found to be coated in a petrochemical goo – the residue of a long-defunct cooking gas plant – that the raging waters of Alenaio Stream had unearthed from below a scour basin at the end of its course. The concrete channel in Alenaio Stream itself, on which work was completed just three years earlier, was undercut and scarred, as was the channel on the Waiakea Stream, similarly armored back in the 1980s. Months later, total flood damage was placed at about $70 million.
On November 5, 2001, federal and county agencies released a status report on 136 separate public assistance projects to address flood damage. The total estimated cost of these projects came to $18,029,773. Of that, projects whose total costs have been pegged at $14,008,876 are to be paid largely, if not entirely, by three federal agencies: the Federal Highway Administration, the Army Corps of Engineers, and the U.S. Department of Agriculture’s Natural Resources Conservation Service (NRCS).
When life and limb are in peril, a kind of shoot-first, ask questions later attitude prevails. Questions that are customarily asked and answered with all due deliberation are set aside for the moment in the effort to re-establish a climate of normalcy. And so it is that emergency declarations have the effect of suspending laws that would otherwise require full public disclosure of environmental effects of projects proposed by state and federal agencies.
When projects involve rebuilding existing structures, the disclosures that might be made in an environmental assessment or impact statement are, in a sense, moot. The rebuilt road or repaired bridge will have an impact no greater or less than what it had before it was damaged.
A year after the disaster, though, the immediacy that attaches to reopening lifelines and removing imminent hazards has waned. Of the $18 million that agencies have allocated to repair flood damage, roughly a third — $6.2 million – has been spent. Most of the large projects, including road and bridge work, stream “flood control” systems, and armoring of stream banks, are still in the design or preliminary contracting stages. None of the public agencies involved has prepared or is planning to prepare any environmental assessment or environmental impact statement for any of the projects.
Soon after the flooding, the county Department of Public Works asked the state Commission on Water Resource Management whether any of the planned projects might require a stream channel alteration permit from the commission. (The county was fined by the commission in the mid-1990s for failing to obtain a permit for construction of the Alenaio flood control project.)
On January 16, CWRM director Linnel Nishioka responded, informing the county that just one of the 14 projects the county planned would be subject to a state stream permit: the construction of a new channel wall on the Waipahoehoe Stream as it crosses under Chong Street (Waipahoehoe is a tributary of the Alenaio).
Juvenile Delinquency
In the last millennium, the Hilo landscape has seen vast changes. Before the arrival of the first human settlers, it was almost certainly a huge wetland. Between the perennial Wailuku River on the bay’s north side and the mouth of the Wailoa River to the east flowed a system of ephemeral streams and tributaries whose natural channels to this day remain poorly mapped over most of the streams’ reaches.
Hawaiians developed hundreds of acres of taro lo`i (fields) and fishponds along the crescent bay. When floodwaters turned the intermittent streams of Alenaio, Waiolama, and Waiakea into roaring torrents, the Hawaiians were prepared to handle it. Although the bayfront was the site of concentrated human activity, according to early maps, Hawaiians were astute enough not to build their homes in the area.
Only after the arrival of Europeans, with their proclivity to build permanent structures on improvident sites, did flood control become an issue. Starting in the late 1800s, the taro lo`i and fishponds of the Hawaiians were filled with hundreds of thousands of cubic yards of sand dredged from the bay. A railroad was laid along the shore, while ship landings and commercial buildings arose on either end of the bay. Sandwiched in between were communities of immigrants brought to the island to work in the sugar plantations that sprang up on the previously forested slopes surrounding the town.
All this development has occurred on what geologists think of as a landscape still in its infancy. The Mauna Loa lava flows on which Hilo is built are of recent vintage, with the last occurring as late as the 1880s. Even in a climate as rainy as that of East Hawai`i, it takes eons for water to carve well-defined streams in new rock. Until that occurs, much of the natural surface water runoff occurs in the form of sheet flow, which is captured near the coast in several relatively shallow intermittent stream beds that feed into Waiakea Pond and then, through the short Wailoa River, empty into Hilo Bay.
There’s another odd characteristic about this youthful land: many of the stream channels, still in their formative years, are interrupted. Try hiking up the Alenaio Stream between Komohana Street and Kaumana Drive. A few hundred yards past Komohana the stream channel vanishes. By the time you pick up Alenaio just downstream of its crossing under Kaumana at Chong Street, the channel is again deep and well-defined – and goes under a different name: Waipahoehoe Stream.
“You’re dealing with a very young environment, geologically speaking,” says Rick Fontaine of the U.S. Geological Survey in Honolulu. And, he adds, confounding the flow of water across the featureless surface are the “interconnections with lava tubes,” a largely unmapped system of underground plumbing.
“The hydrology and flood hydrology of the greater Hilo area are definitely complicated,” he says.
On the Map
According to a state-maintained website on natural hazards, [url=http://www.mothernature-hawaii.com,]www.mothernature-hawaii.com,[/url] a damaging flood occurs on the Big Island every two years. But the averages don’t hold for Hilo and Puna, where between 1980 and 1994, 18 flood events occurred.
The most recent draft update of the Hawai`i County General Plan devotes several pages to flooding. “Present drainage and flood problems are mainly due to the development of vacant lands, which are often subject to serious flooding without any commensurate, coordinated development of new drainage systems or expansion of the existing drainage systems,” the plan states. While planners rely on Flood Insurance Rate Maps – FIRMs – developed by the federal government to steer development away from flood-prone areas, these maps are notoriously inaccurate. Current FIRM maps “are not very accurate as to the location, position, and formation of geographic and geologic attributes,” the draft plan says. “Furthermore, there are many areas where there is no data to determine the flood potential.”
After the November 2000 flooding, the county, with Federal Emergency Management Agency support, hired a contractor to redraw FIRMs for the areas around Waiakea and Palai Streams. Typically, FIRMs indicate areas that will be underwater in a 100-year flood and a 500-year flood – floods that have a 1 percent and a 0.2 percent chance, respectively, of occurring in any given year.
But what constitutes a 100-year flood and how is it figured? The USGS’ Fontaine described a variety of ways that hydrologists use to calculate expected 100-year peak discharges in a given stream. Federal agencies generally agree on something called a log-Pearson type III approach. “It’s just a type of statistical analysis,” he says, that considers stream-flow data from monitoring gauges, the watershed area that drains into a stream, and rainfall patterns within that area – among many other factors. Should one element in the equation change – if, say, a subdivision is built whose roads and houses increase the impervious area in a watershed, or a highway is laid that interrupts natural drainage, or a forest is cut – the hydrology of the area changes as well. And it’s back to the drawing board to calculate peak 100-year flows.
Even in the best of circumstances, determining the 100-year flood levels is more art than science. “You’re trying to estimate something that’s a very rare quantity,” says Fontaine. “It’s something that over the long term will occur just every 100 years. Of course, you could get two 100-year floods back to back.” And if you are trying to predict floods for streams where sampling information is meager, the calculations are all the more imprecise.
Were all this not bad enough, estimating floods in Hilo was made tougher yet when the USGS discovered that one of its Hilo employees was submitting falsified data on stream flows over a period of several years. The employee was fired, but the loss of years of data is still being felt.
Antedeluvian Records
Some of the worst damage in the November 2000 flood occurred along the areas drained by the Palai and Waiakea streams. The Palai watershed had not been well mapped up to that point. The Waiakea watershed had been better studied; in the 1980s, a traditional steep-walled flood control channel was installed from Waiakea Pond, near the coast, to the area near the University of Hawai`i at Hilo. As residential subdivisions marched up the 35-square-mile watershed drained by the Waiakea Stream, the natural watercourse was walled and channelized where it passed through and along housing developments.
URS Corporation, which was hired by the county to redraw flood maps – and recalculate 100-year flows – for the Waiakea and Palai watersheds has reset the clock, so to speak, on 100-year floods. The bar has been raised, and now the November 2000 flood record has come to define the new 100-year peak flood. More precisely, the flooding experienced that month was something less than what Hilo can expect to experience once every 100 years.
According to Ray Lenaburg of the Federal Emergency Management Agency, “we have come up with a new 100-year [flood] discharge, and that’s what we’re using in the new maps.”
“The old peak discharges have been superceded based on a new analysis,” Lenaburg told Environment Hawai`i in a telephone interview. The new figures, he said, came about after a consultant reviewed data from two gauges in the area and ran them through the standard log-Pearson 3 method of determining distribution.
“We thought it was a one-in-100-year flood,” Lenaburg said of the November 2000 event, “but when we went back and looked at the data, it was less than a one-in-100 year flood.”
To protect built-up areas from future floods, the county and the Corps of Engineers have begun to work on a multi-year project that will lead eventually to construction of a mile-and-a-half-long channel and another 1,100-foot-long levee along an existing channel. The new channels would cause the flow in Waiakea Stream to be divided into two watercourses above the Kupulau Bridge, site of some of the heaviest flooding in 2000. The two branches would rejoin at the start of the channelized Waiakea Stream, near the bridge at Komohana Street.
The project, if it works out, won’t provide relief for homeowners for a while yet. At a December meeting with concerned members of the public, county engineer Dennis Lee outlined the Corps’ best-case timeline. From January 2003 to January 2005, the feasibility study will occur. Another year – July 2005 to July 2006 – will be required to draw up plans and specifications. Barring unforeseen delays, construction might be completed by July 2008. The estimated cost is on the order of $17 million.
Besides the new work on the Waiakea Stream, the Corps of Engineers will be repairing flood channels on Alenaio Stream and the lower reaches of Waiakea Stream, channelized in 1985. Total cost of repairs is put at about $4.2 million.
Double Whammy
If the county takes what was naturally sheet flow and directs it into channels at ever-higher elevations, won’t that just make problems worse for people living downstream by adding to the volume of water in streams at lower elevations?
The question was posed to Ben Ishii of the county Department of Public Works. Ishii is the county engineer working most closely with the Corps of Engineers in designing future flood control projects.
Ishii responded by pointing out that sooner or later, most sheet flow ends up in drainage channels such as Waiakea and Alenaio anyway. Directing flows to the channels upstream would not create any real problem, he said.
-Rick Fontaine, USGS
Yet Fontaine of the USGS had a slightly different take. “Anytime you put in an artificial channel to direct or deter runoff, you’re probably reducing the time it takes the water to get to the channel,” he said. “So you have a timing issue as well, now. If you have a heavy rain in the watershed, your peak flow will occur at a certain time that has to do with how long it takes water to get into the channel. Depending on how you alter the natural timing, you could lower or raise peak flows. You could increase both the volume and peak flows if you induce more water to come into the channel at the peak flow time. You could be producing a double whammy, because you make that water get into the channel faster than it otherwise would.”
On the other hand, Fontaine added, if the planning were done right, “you could also reduce peak flows” by adding artificial channels.
In the meantime, draft revisions to the Hawai`i County General Plan would steer the county in the direction of greater flood plain protection and other more natural ways of protecting structures against floods. Whether the result will be anything more than exhortatory is — in the face of pressure from the Corps of Engineers, the Department of Public Works, and the vast army of private and public agencies whose livelihood depends on harder solutions — anyone’s guess.
Melanie Mishata, an intern with Environment Hawai`i from the University of Hawai`i at Hilo, assisted with the research for this article.
— Patricia Tummons
Volume 12, Number 7 January 2002
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