WENATCHEE — By next spring, members of the Wenatchee River’s oldest water-users association are going be “under pressure” for the first time since the group formed in 1896.

The Pioneer Water Users Association, together with the conservation group Trout Unlimited, Monday began work on a $3.5 million project to transform their historic gravity-fed, earthen irrigation canal into a pressurized pump-driven system of underground pipe.

The system will reduce needed flow by about half, without sacrificing delivery of water. Less will be lost to evaporation or leakage, and water will only flow when users need it.

That means more water will remain in the Wenatchee River for fish.

“The only time the system will be running is when one of the users turns the water on,” Dan Jaspers, manager of the system, said Monday during a tour of the project.

Aaron Penvose, hydrologist for Trout Unlimited, agreed. “We’re both excited to see it get to the construction phase... This project is a win-win for all parties and a model of collaboration on water issues in the region.”

The project is funded entirely by a package of local, regional, state and federal grants that Trout Unlimited has been assembling since 2008, Penvose said. All 17 needed permits have already been approved.

Groundwork has begun for the pumping station, which is along the north shore of the Wenatchee River, just upriver of the Apple Capital of the World sign at the city’s entrance.

The five-pump station will replace the system’s current inlet, farther upriver in Monitor.

The approximately 6.5 miles of open, earthen canal north of the river will be enclosed in a specialized plastic pipe of between 24 inches and 8 inches in diameter.

Most of the association’s 105 users would be supplied from this new pressurized line. Thirty of its users near Walla Walla Point Park will be served by a separate system, supplied by a recently drilled area well.

One part of the system, an aged and deteriorating pipeline that passes under a now densely developed portion of North Wenatchee will be decommissioned.

A defect in that part of the system caused a large “sink hole” to open on North Miller Street in 2011, causing an extended traffic detour on one of the city’s busiest streets.

Jaspers says that the water-delivery technology of the current system remains virtually unchanged since it was created by Arthur Gunn in 1896 to transport water to the region’s young orchards.

During irrigation season, water constantly entered the system at an inlet about a mile upriver from Monitor and flowed “downhill” some 9 miles past users’ properties. The canal system emptied into the Columbia River at the foot of Ninth Street.

Most users had to have their own pumps to transport water from the canal to portions of their properties.

Open, earthen canals have been vulnerable to beaver dams, washouts and leaks from gopher holes, Jaspers said. They required constant maintenance and monitoring.

The new system will pump water to users upriver. Spigots will replace individual pumps, Jaspers said.

Work will continue this winter and be finished by April 1, he said.

Christine Pratt: 665-1173

pratt@wenatcheeworld.com