Hilo Bay’s water quality could be improved in the future following a planned watershed study.
After the bay was found to not meet state water standards in 2009, county, state and federal agencies have investigated various methods for improving it. The most significant of those possible solutions, as suggested in a 2009 study by the U.S. Army Corps of Engineers, would be to modify the Hilo Bay Breakwater to improve water circulation.
Under the working theory that the century-old breakwater was trapping sediments from the Wailuku and Wailoa rivers, the Corps hypothesized that opening gaps in the structure would allow those sediments to circulate out of the bay.
The Corps initiated a second study in 2021 to determine how effective that solution might be, and the results, published in February, suggested that it might be very effective — but not without major caveats.
In particular, the Corps estimated that opening gaps in the 10,080-foot structure would cost upwards of $50 million while also creating unpredictable wave action and currents in the bay.
The report listed two other possible modifications to the breakwater that would similarly improve circulation but with similar drawbacks. One of them, a seawater exchange system modeled after one installed in Jumunjin Harbor in South Korea, would allow seawater and sediment to pass through the breakwater, but also would cost more than $50 million. The other modification, a circulation pump system, would be simpler but no less expensive, according to the report.
The 2021 study also listed several other, less pricey, potential actions to help improve the bay’s water quality.
Hawaii County Research and Development Director Douglass Adams said the county is pursuing at least one: a comprehensive study of the Hilo watershed in order to determine how, exactly, contaminants are entering the bay.
“We’ve got to gather this data so we can look at the problem scientifically,” Adams said, adding that the county hasn’t done sufficient due diligence to determine whether a $50 million civil engineering project is an appropriate solution for the problem.
Adams said the county has applied for grant funding for the study through the National Oceanic and Atmospheric Administration. The results of that application should be revealed within a few months, he said.
Should NOAA grant the county funding, Adams said the county will work with other partner agencies, including the Army Corps of Engineers, to carry out the study. But, he added, it is still to early to set a timeframe for when the study might begin or end.
“What’s important is that we’re not waiting,” Adams said. “We are working on this now.”
Adams said that the bay is the “bread and butter” for many in the community, and needs to be maintained.
Stan Lawrence, a fixture in the surfing community for decades and owner of the Orchid Land Surf Shop in Hilo, said the state Department of Health should implement more frequent water-quality monitoring and testing at the bay, and make that data easily available to the public. But he also wondered whether there’s anything that people can do to significantly improve water quality further.
“Anywhere there’s rivers, they’re going to carry sediment,” Lawrence said. “It’s been fine for now, since we’re in these drought conditions, but when it rains heavily … you know, animals go to the rivers to drink, and they leave excrement by the river and that gets swept away in the rain.”
Lawrence added that, over the last 50 years, water quality in the bay has improved substantially after the end of the island’s sugar plantations, which he said contributed a significant amount of pollution to the watershed.
Lawrence said that modifying the breakwater would be “a waste of time.” Even if it works to improve the bay, he said, sediment from the rivers could then be carried to Keaukaha, thus spoiling other popular waterfront areas.
“We can’t know all the ways it could impact things,” Lawrence said.
Email Michael Brestovansky at mbrestovansky@hawaiitribune-herald.com.
