Dredging Ala Wai improves its capacity, not cleanliness

QUESTION: How often is the Ala Wai Canal dredged? Does the pollution get cleaned up by this procedure?

ANSWER: Second question first: No, dredging does not get rid of pollutants and will not make the canal safer for swimming or eating fish.

It’s meant mainly to improve the capacity of the canal, which was built as a drainage channel and sedimentation basin.

The Ala Wai Canal was completed in 1928 and has been dredged only three times since: in 1966, 1978 and 2004.

The next dredging won’t take place for at least a few more years.

The purpose of dredging the canal is to restore its flood-carrying capacity and maintain it as a navigable channel.

"Increased sediment reduces the canal’s flood-carrying capacity as well as its ability to settle out sediment transported into the canal from various sources throughout the watershed," said Deborah Ward, spokeswoman for the state Department of Land and Natural Resources. "Trapping the sediments in the canal also minimizes the sediments that enter our nearshore waters."

While sediment and any pollutants within the sediment are removed during dredging, "the intent of the dredging is not to improve the water quality for recreational purposes," she said.

Hence the Department of Health’s advisory not to swim in the canal or eat the fish or other seafood from it.

A task force has recommended that the canal be dredged every 10 years.

While a 10-year dredging interval can be a good general rule of thumb, DLNR contends the canal should be dredged "when there is need and sufficient accumulation begins to impact its flood-carrying capacity or navigation," Ward said.

That could mean earlier or longer than 10 years.

DLNR did a quick assessment last year, which identified accumulation of sediment near the confluence of the canal with the Manoa-Palolo Channel, Ward said. 

However, the assessment did not show significant accumulation in other areas of the canal.

With an eye on the next dredging, DLNR has requested planning and design funds, "anticipating that by the time we are able to prepare the design plans, obtain all of the environmental permits and secure construction funds, the timing should be about right," Ward said.

NEXT DREDGING

DLNR has asked the state Legislature for $2 million for fiscal year 2015 for the planning, permitting and design for dredging the Ala Wai and improving canal walls.

"We are waiting for legislative conference hearings to be over before we can confirm amounts," Ward said. (The Legislature is scheduled to adjourn Thursday.)

DLNR plans to request construction funds in the next biennium (fiscal year 2016 or 2017) when it has a better idea of the estimated construction cost, she said.

The schedule for dredging would depend on getting funding and permits.

Ten years ago it cost $6.5 million to dredge and remove approximately 185,000 cubic yards of material from the Ala Wai.

Ward noted this is a 10-plus-year-old price, and new costs will depend on how much material will be removed, with inflation to be factored in.

Monday: Monitoring pollutants

MAHALO

To a young man, whose name I didn’t get, who saw me in my stalled Corolla on Dillingham Boulevard, across from Honolulu Community College, during rush hour at 4:45 p.m. recently. I was stranded without a cellphone. This young man parked his truck and offered help. He hunkered down and pushed my car over to the HCC parking lot, out of the gridlocked westbound lanes of Dillingham. With horns blaring and motorists irate at being stuck, it was a little tense. He declined to accept anything but my thanks, saying with a smile, "Have a good day, bruddah!" An Oceanic Cable guy also came over, and I was able to call for help on his cellphone. Mahalo for the kindness of strangers. For a guy who relocated from Seattle, your aloha means a lot. — Joe Hilldorfer

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