Postcards from the Drought: Fort Bragg desalination plant ready to be called into service

A pair of recent showers has swelled the flow of the Noyo River near Fort Bragg ever so slightly.

This comes after weeks when the river ran at a trickle so low the city was often forced to turn off the intake pumps that feed water to the town’s homes and businesses.

Though located about 4½ miles from Noyo Harbor, the water supply at Madsen Hole, where the intake pipe meets the river, was overwhelmed in recent weeks by brackish tidewaters that pushed upstream.

Last weekend, crews installed a newly acquired mobile desalination plant that can be called into service when salt concentrations at the diversion point rise too high.

“We don’t have many other options, either,” Fort Bragg Public Works Director John Smith said. “We’re kind of counting on the thing, so hopefully it operates as we expect.”

The city of about 7,300 people gets surface water from two tributaries in addition to the Noyo River but relies more heavily during the warmer months on the water from Madsen Hole, which provides about 60% of its summertime supply.

After two years of historically low rainfall, the shrunken river has been especially vulnerable to saltwater intrusion. In anticipation of trouble, the City Council approved the purchase of a reverse osmosis unit back in June.

The $335,000 mobile plant, acquired with emergency drought funds from the State Water Resources Control Board, will only be used as a last resort, Smith said.

The city has progressively upgraded its water shortage status over the summer, in the meantime. In mid-September, residents were ordered to use 30% to 40% less water than a year ago.

The desalination plant can filter up to 288,000 gallons of water a day. Regulatory limitations on disposal of the resulting brine into the city sewer plant allows for processing of half that much, however — 144,000 gallons per day, Smith said. The city uses about 550,000 gallons daily, he said.

The city installed a fallback reservoir in 2015, during the last drought, roomy enough to hold 14.7 million gallons of water. But it is fed by a wintertime spring, and officials are trying to stretch the declining storage as much as possible, Smith said.

Even with low river flows, Smith said, there’s usually no problem with the river intake until tides reach around 6 feet or higher, like those arriving in a couple of days and expected to last about a week.

But the river at Madsen Hole may be running just high enough at present to prevent a problem, thanks to two minor storm systems that came through the area about a week and two weeks ago. Combined, they left behind an inch or so of rain throughout the watershed, the National Weather Service said.

Though still low, the river is now flowing at rates above 3 cubic feet per second — levels not seen since June — so it’s possible the desalination unit won’t be needed any more this year, depending on the arrival of autumn rains, Smith said.

Postcards from the Drought is an occasional photographic series aimed at reflecting the impact living with the drought continues to have on us each day. We welcome your suggestions. Email us at drought@pressdemocrat.com.