Professor Eric Benbow of Michigan State University said that from a purely scientific perspective, he'd like to see all diversions ended, but he recognized that some diversions will continue.

Benbow did his dissertation research on Maui and has been wading the four streams "eight hours a day, seven days a week" on periodic visits to Maui since 1994.

Dr. Lawrence Miike of the state Commission on Water Resource Management, who is the hearings officer, said he was uncertain exactly what Benbow meant by "75 percent of median flow." But whatever the precise amount, it would be a lot.

The four streams are harvested of 50 million to 60 million gallons a day, under interim in-stream flow standards controlled by the commission. The hearing is collecting evidence in order to establish permanent flow amounts.

Hawaiian Commercial & Sugar Co. presented an expert witness who queried whether computer modeling and releases based on a percentage of some flow would be the best way to determine how flows affect life in the stream.

John Ford of SWCA Environmental Consultants said he would recommend releases of set amounts of water at different times.

"Use an approach of active management," he proposed. "See what really happens rather than trying to model it."

One reason, he explained, was that the computer model used by the U.S. Geological Survey in East Maui and proposed for Na Wai Eha, has not been validated for Hawaii streams.

He used the model, called PHABSIM, for Physical Habitat Simulator, in the 1980s. It had its uses, he said, but it limited its parameters to water depth, water velocity and kind of substratum. Ford said that might not adequately determine the quality of habitats.

Benbow also made the point that quantity is not necessarily the important factor in determining the impact of changes in a habitat on the animals that live in it.

If you shrink the quantity of habitat – for example by draining water off into an irrigation ditch – you may "change the quality of the food resource of invertebrates, and that will more than likely affect the food web interactions."

The main focus of testimony about stream life before Monday had been on the large native species that are amphidromous (move between salt and fresh water) – oopu, opae and hihiwai, which are, respectively, a fish, a shrimp and a mollusk.

Benbow and Ford both testified that good baseline studies are needed to determine what's in the streams now.

Just since September, Ford said, he has climbed to the 1,600 foot elevation of the streams. There he found oopu ranging from scarce to uncountable – in one area they "carpeted the streambed."

Those were all populations above the diversions. The effects of the diversions were the key point, since the small (postlarval) animals migrate back from the sea and try to swim to the higher reaches of the streams.

They cannot do this when the streams are dry, but Ford testified that it is not clear that the streams must flow mauka-to-makai continuously for them to keep populations alive above the diversions.

Ford, who has done work on streams in the islands since 1974, recounted how in the 1980s the oopu was proposed for the endangered species list.

As part of that process, streams across the state were surveyed. Ford said biologists were stunned to discover oopu and shrimps living high up in leeward streams that were dry most of the year.

Benbow said he was concerned about the long-term viability of stream populations.

His specialty, insects, are turning up with much greater diversity now that they are being studied more intensively, he said, with many species not yet scientifically described.

He said some reaches of streams below diversions in Na Wai Eha have 80 percent to 90 percent of their natural impact "severely impaired."

"We don't really know what we're losing at the species level," he said.

That is why he recommended a generous and long-lasting restoration of stream flows, both to get a habitat to study and as a protection if there should be a prolonged drought.

Schulmeister asked, "If (oopu, opae and hihiwai) had been declining precipitously for over 100 years, wouldn't they be gone?"

"They are present, we don't know what the population is," said Benbow.

He said he is concerned about the viability of the populations over the indefinite term.

The hearings resume today at 9 a.m. at the Cameron Center and are scheduled to continue through Friday.