Nature's fury teaches engineers hard lesson

The six weeks of storms that brought death and destruction to Hawaii also delivered replenishing relief to the islands' environment.

Underground water supplies were restocked, debris was washed out of streams and nutrients from land fed offshore reefs.

The adverse environmental effects of the record drenching tend to be where rushing water met man-made obstacles, observers say. That is where landslides and floodwaters push buildings, roads and sewage systems to the breaking point.

"The environment benefits from rain, even heavy rain," said Don Heacock, the state Department of Land and Natural Resources aquatic biologist on Kauai. "What the environment doesn't benefit from is how mankind changes that environment."

Recent storm-related events provided numerous examples of that axiom, including:

» In Hauula on Oahu's Windward side, a rerouting of Maakua Stream jumped its man-made bank after heavy rain March 8 and ran down Hauula Homestead Road, driving neighbors to use sandbags, boards, concrete blocks and even cars to divert floodwater from their homes.

» Water stored in Kauai's Ka Loko Reservoir became a deadly torrent when it breached the dam March 14, killing seven people and destroying homes downstream.

» Some residents of Maunalaha and Manoa valleys saw their picturesque homes on steep mountainsides and near stream beds become danger zones when landslides and mudslides made repeat visits in late March.

» World-famous Waikiki beaches were temporarily closed by a bacterial contamination from a mammoth raw-sewage spill. One man's death and two women's illnesses might have been caused by pathogens in the waste water.

Though Waikiki beaches reopened by April 4, continued poor water quality in the Ala Wai Canal has prompted canoe clubs that normally use it for workouts to relocate because of health concerns for paddlers.

"I think these events reminded people that we are susceptible to flooding and other kinds of disaster," said Derek Chow, a U.S. Army Corps of Engineers senior project manager on Oahu. "Nothing like a good flood to get everybody's attention."

Already, new flood-control studies are being planned for Kaaawa, Waiahole and Waikane, Chow said. And ongoing projects to improve flood control in Kahuku, Laie, Hawaii Kai, Aina Haina and the Ala Wai Watershed should get a boost as well, he said.

In the weeks since the Ka Loko disaster, the state government that had inspected not one dam since 2004 assisted in thorough inspections of every dam in the state.

"If we didn't build in the flood plain, we wouldn't be flooded with frequency we have," Chow noted. "We like being close to our waterways. Look at the housing prices on shorelines and streams. It's obvious that's what we're attracted to."

Yet in Hawaii, as worldwide, much of the natural course of streams has been altered with bridges, dikes, dams and channels, Chow said. While these engineering feats might work under ordinary rainfall, when heavy rain comes, "water's going to jump the bank somewhere," he said.

Still, periodic storms remove sediment from streams, leaving "boulders nice, smooth and clean, which allows freshwater algae to grow on them," Heacock said. That algae is the basic food of oopu, fish that are found nowhere else in world.

Fresh water flowing into the ocean triggers juvenile oopu in bays to migrate upstream and breed, said Dan Polhemus, administrator of the state Division of Aquatic Resources. The flushing of the streams also tends to wash out non-native creatures while making things better for the native ones, he said.

One function of natural wetlands and estuaries is to slow down floodwaters and filter out sediment and nutrients -- keeping them from overwhelming offshore reefs, Polhemus noted.

On April 2, "Maunawili Stream flash-flooded in a really intense way. It roared into the marsh, and the marsh sucked the whole thing up. At the end of the day, the beach at Kailua was clean. You saw very quickly the ecosystem services you get out of that wetland.

"Waikiki used to look like that," Polhemus said. "You had a big wetland behind the beach that we've turned into real estate."

Re-creating at least some wetland buffer zone is a key component of Chow's Ala Wai Watershed flood control project.

On Kauai a flyover of Kauai's North Shore shortly after the March 14 Ka Loko Dam breach seemed to show that the Kalihiwai Stream estuary absorbed some of that flood's force, Polhemus said.

In coming weeks, scientists from the state Department of Land and Natural Resources, National Oceanic and Atmospheric Administration and U.S. Fish and Wildlife Service will survey Kilauea Bay's underwater environment, he said. They will be checking for sediment buildup, algae blooms and reef damage from uprooted trees that might have pounded them like battering rams.

Aquatic biologists also will be watching the areas offshore from the Ala Wai sewage spill for a possible algae bloom. The sewage is not expected to cause any direct kills of coral or fish, he said.

A project to pump offshore sand to Kuhio Beach to widen it was postponed two weeks by the sewage spill but is expected to start tomorrow.

U.S. Geological Survey hydrologist Steve Gingerich called the spate of rain "probably a pretty good recharge event" for Kauai and Oahu's ground-water reservoirs because in addition to flooding, there were periods of "long-term, steady rain."

That is good for long-term water supplies, even though ground-water levels that dropped to record lows between 2000 and 2004 have since recovered to normal levels, he said.