Wednesday marks the 20th anniversary of a Halloween Eve flash flood that sent a tsunami of mud, water and debris up to 8 feet high roaring through the University of Hawaii Manoa campus, damaging 30 buildings and tossing dumpsters and vehicles in its path.

The lives and health of some UH students, faculty and staff were immediately at risk during the flash flood.

In the days that followed, hundreds of UH employees and volunteers worked in darkness to assess damage and salvage research and sometimes priceless documents, some going back to the days of the Hawaiian kingdom.

“There were rare maps from the 16th century that are literally irreplaceable and priceless,” then-interim UH President David McClain told the Honolulu Star-­Advertiser.

McClain had been in his new interim job at UH for just four months.

It would take sometimes years to rebuild parts of the Manoa campus, especially hardest-hit Hamilton Library, at an overall cost of $100 million in 2004 dollars, including insurance and state and federal funding.

The damage led to changes at Manoa, including the creation of UH’s John A. Burns School of Medicine and UH Cancer Center off campus in Kakaako to replace the flood-damaged Biomedical Services Building, which had been the Manoa home to the UH medical school.

The years-long restoration of Hamilton included new designs intended to prevent future flooding.

It was a stormy Saturday night when 10 inches of rain poured into Manoa Stream, leading it to become clogged with debris and overflow its banks at Manoa Marketplace, unleashing a flash flood downstream at UH.

The worst damage struck Hamilton, the UH system’s flagship library, entrusted with storing and making historical documents available to the public.

A small class was underway in Hamilton’s basement. Members of the class had to kick out a window and form a human chain to escape the rushing flood pouring down on them from all directions, including stairwells that otherwise would have provided escape.

A professor working that night contracted leptospirosis in his research lab and was later hospitalized after he was suddenly swamped by 4 feet of bacteria-­contaminated stream water.

McClain and and his wife, Wendie, had been dining at the then-Kahala Hilton with another couple when McClain received a call about the damage, especially to Hamilton Library.

McClain remembers being told, “You should get over here.”

They drove in a downpour to Hamilton and arrived sometime around 8:30 p.m.

Librarians and other UH staff already were there and making plans for how to preserve some of the rarest possessions in the library collection, amid “hundreds of thousands of other documents,” McClain said.

Library officials knew the best way to begin the restoration process was to first freeze soggy documents that were part of history valued at $34 million in 2004 dollars.

Jim Nishimoto, executive assistant to McClain, used his Teamsters Union connections to have five freezer containers delivered to UH in the coming days.

Most of the documents that were frozen were later shipped to Texas for restoration, while UH librarians learned how to preserve other documents after setting up new operations at Dole Cannery and Sinclair Library that continued during Hamilton’s rebuilding.

But there were only enough containers for just a fraction of the hundreds of thousands of damaged documents, which meant painful decisions to discard the bulk of the collection.

“We ended up throwing away tons and tons of stuff,” said Gwen Sinclair, department chair and librarian for government documents and maps at Hamilton Library.

“I really hated having to throw away a set of books called the U.S. Congres­sional Serial Set going back to the early 19th century,” she said. “It had reports of exploring expeditions with maps and botanical illustrations. And there was a set owned by Prince Kuhio telling the story of the Civil War.”

The good news, Sinclair said: “We saved all of the Pacific and Hawaii and Asia maps. Some were cleaned here, and all of our rare maps were saved. Some have mud stains but they are still usable. We developed the capacity to clean maps and aerial photography. The flood ended up being a learning experience, even though it’s not the way you want to learn things.”

In the days after Manoa Stream unleashed its flood, Sinclair said most of the documents left behind at Hamilton Library became “covered in mold.”

Library workers tried to dry out some books on makeshift clotheslines strung around Hamilton.

The night of the food, she and her husband, Steve Pickering — Hamilton’s building manager — were asleep when they were awakened by a phone call around 10:30 p.m.

They were only told that “our network administrator went to respond to an alarm on a computer server and found an emergency at the library.”

So they were unprepared for the scene they were about to be greeted by.

The downpour had stopped by the time they drove down Maile Way to an uncharacteristically darkened campus, which had lost power and computer servers mostly stored in building basements.

“It was cloudy with no ambient light, so it was eerily dark,” Sinclair said.

The flood was so powerful that it carried away dumpsters from outside Hamilton and into the street.

Inside, Sinclair and Pickering had to use flashlights to peek into the library basement and saw a muddy mess.

A line of mud provided fingerprint evidence that the flooding was 8 feet high before the flood receded.

Books swollen by moisture could no longer fit on their shelves, leaving “heaps and heaps of books all over the place,” Sinclair said.

Workstations were unrecognizable and tossed about everywhere, along with other furniture, office equipment, broken metals and debris.

Elevator doors were contorted and unworkable, and “we saw a photocopy machine that had been picked up and moved,” Sinclair said. “Something terrible had happened. This was a disaster of a major magnitude.”

The basement was slippery with mud and the floor above remained soaked with water over the days that followed until a professional team took over Hamilton to begin the cleanup.

On the first night, Sinclair said, Hamilton already “smelled horrible. It was gross down here. Everything was covered in mud.”

Hundreds of people converged on Hamilton over the following days and had to go through every conceivable place where documents might be stored to make sure none were overlooked in the process to triage what could be saved.

While working, library staff often got caught and cut by metal and debris and had to receive tetanus shots, along with the risk of breathing in mold spores.

Their work clothes suddenly included rubber boots, headlamps and lanterns as if they were going down into a coal mine.

The flood risked the lives of others.

Andrew Wertheimer, an associate professor of library sciences, was teaching a Saturday night class in Hamilton’s basement when the class had to break a window to escape as rushing mud and water poured down the stairwells that otherwise would lead them to safety.

“They had to break a window to save themselves,” McClain said.

UH professor Terrence Lyttle was working in his Biomedical Sciences Building lab on cell and molecular biology when water 4 feet deep roared in, costing Lyttle 35 years of genetic research and putting his life at risk.

While inspecting the damage to his flooded lab, Lyttle contracted leptospirosis and was hospitalized weeks later for three nights with a temperature of 104 degrees. He lost 20 pounds.

Leptospirosis has been fatal in Hawaii, and Lyttle was 56 at the time.

People regularly are exposed to leptospirosis on all islands when wading or swimming in freshwater sources like Manoa Stream, rivers, ponds and waterfalls that frequently become contaminated with animal urine. They’re especially vulnerable when they have open cuts or blisters.

McClain called all of the survivors and staff who were at UH the night of the flood — and the hundreds of people who kept coming back — “heroes.”

“It was traumatic for them to have water coming into their workspace,” he said. “They love their jobs. These folks are just incredibly dedicated. … I felt privileged to play some small role to the resolution for the campus.”

Donations to Hamilton poured in from libraries across the country that replaced some of the damaged items, especially from Brigham Young University Hawaii’s Joseph Smith library and UH Hilo, Sinclair said.

Much of the donated material, she said, “for the most part was all stuff that we needed since we’re a federal depository that belongs to the federal government.”

Rebuilding Hamilton occurred in phases, and it was finally fully reopened in 2010.

A moat around Hamilton that allowed floodwaters to pour in was sealed, and drains were engineered to divert future floods away from the library, along with other changes including replacing plasterboard with concrete.

A freezer also was installed and a role of preservation specialist was created to respond to future water damage to library materials.

UH had its information technology operations spread around the campus, typically in building basements that were deluged by the flood.

In the aftermath a new IT Center opened 10 years later, in 2014. Now-UH President David Lassner was in charge of information technology services at the time and will retire in December as UH president.

“Twenty years later,” Lassner told UH’s Malama­lama publication, “we stand stronger, united by the lessons learned and the community spirit that emerged from that devastating night.”

Like other aging government buildings across Hawaii, UH has had its share of leaks and drips, Sinclair said, “but not a flood where everything is covered in mud,” she said. “None of us had ever experienced anything like that.”