OREGON STATE UNIVERSITY

OSU develops fish-friendly tide gate

02/18/1998

CORVALLIS - A newly designed tide gate may help salmon make a safer passage to the ocean while farmers keep their coastal lowlands productive, thanks to the research of an Oregon State University graduate student and OSU's Coos County Extension Service office.

The new device is the first significant modification to traditional tide gates - sometimes called tidal boxes - in more than 100 years, said Paul Heikkila, a watershed specialist and Extension Sea Grant agent with OSU in Coos County.

For the century that people have lived and farmed on the Oregon coast, they have held back the incoming tide by channelizing coastal streams and then placing gates at the mouth of the culvert or channel.

Another widespread use of the tide gate is in placing dikes along tidal marshes to keep them dry. The tide gate allows upland drainage at low tide, but keeps tide water and high river flows in the main channel. But marshland is important for rearing small salmon to ocean-going size, and tide gates hinder that development.

A traditional tide gate acts like a flap at the end of a pipe: It opens to let water flow out to the sea and closes when the tide starts to come in.

This worked well for farmers, but it also meant that small salmon smolts were sometimes swept out to sea before they were ready, Heikkila said.

"The adults had to hang around and wait, but the juvenile cohos are always looking for low gradient wetland areas and creeks for winter rearing habitat," Heikkila said.

The adults are waiting for either an opportunity to swim through the tide gate to an upland spawning area or for the opportunity to head further upstream. In either case, adult salmon are strong enough to handle river currents without having to seek quiet channels.

Juvenile salmon are not strong enough.

"And one of the concerns is that these (tide gates ) restrict passage for juveniles - they get flushed out to the river and down to the ocean before their bodies are acclimated to salt water," Heikkila said.

OSU graduate student Jay Charland was working for the Coquille Watershed Association last summer when he had an idea for a kinder, gentler tide gate.

It was a simple modification: His tide gate opens in the middle like a pet door, but it is hinged at the bottom instead of the top. The addition of a float arm allows the water to slowly open and close the gate, controlling the speed of the water as it passes through the gate and creating short periods where the gate is open and the water calm.

The result is that the box may increase passage for fish by about 50 percent, Heikkila said. That is significant because many of the tidal regions of coastal streams and wetlands that nurture small salmon also have been modified by tide gates.

Charland, a graduate of the Marine Resource Management program at OSU, built a model of the tide gate and tested it. Now working for the Tillamook Bay National Estuary Project, he may get to see his invention tested this summer.

The Coquille Watershed Association, with help from Pam Blake of the Oregon Department of Environmental Quality and funding through the federal Environmental Protection Agency and the Coos County Extension Office, is planning to test the new tide gate on Hatchet Slough Drainage on the Coquille River.

Pre-experiment monitoring to see how the fish are passing through the existing tide gate is nearly completed. The old gate will be pulled off this spring, and the new model put in its place.

The tide gate experiment is only one of many under way by the Coquille Watershed district, with cooperation of many local landowners, to restore many of the coastal marshlands and streams to natural - or more natural - conditions.

"With this pet door tidal box it is like 'Why didn't we think of this before?'" Heikkila said.

If the device lives up to its promise, it may replace its 100-year ancestor as the new model for living in cooperation - not conflict - with the forces of fish and tides.