By DAN WHEAT

Capital Press

WENATCHEE, Wash. -- One of the oldest agricultural irrigation systems in Washington is getting a $3.5 million facelift this winter.

The 116-year-old Gunn Ditch, operated by Pioneer Water Users Association, is a small system of only some 8 miles of canals and pipes serving 107 users from the community of Monitor to the northern edge of Wenatchee.

It was regarded as an engineering marvel in its day for a siphon pipe carrying water on a bridge across the Wenatchee River next to a larger siphon pipe for the Wenatchee Reclamation District's Highline Canal.

But for several years, the association, Trout Unlimited, the state Department of Ecology and other state and local agencies have been redesigning the system to dramatically decrease its water use. The idea is to keep more water in the lower few miles of the Wenatchee River for fish during the April-to-October irrigation season and particularly the low flows of August and September, said Dan Jaspers, association manager and project manager for Trout Unlimited.

The overhaul is just beginning with excavation of the Wenatchee River bank next to the Wenatchee River Bridge on the northern entrance to town. A pumping plant will be built there to send water from the river northward into a pressurized pipe replacing the open canal to Monitor. The intake a mile upriver from Monitor Bridge will be closed. The siphon -- for Gunn Ditch only, not Highline Canal -- across the Wenatchee River at Wenatchee will be decommissioned and a new well will feed the lower portion of the system including orchards along Walla Walla Avenue in northern Wenatchee.

The upper portion will use just 3 to 8 cubic feet of water per second at any given time of demand versus the continual flow now of 35 cfs through the canal, Jaspers said.

P.O.W. Construction, of Pasco, is the general contractor. Work is to be completed by April 1, in time for the next irrigation season.

The fact that water will only flow when needed instead of continually flowing is a benefit to irrigators and a huge benefit to fish, said Aaron Penvose of Trout Unlimited.

Penvose was instrumental in getting local, state and federal grants to fund the project so that system users are not billed, Jaspers said.

The system still serves a number of orchards but fewer than years ago and more residential yards.

Four 75 horsepower pumps and one 25 horsepower pump will be installed, Jaspers said. They will provide water through a 24-inch pipe that narrows to an 8-inch main by the time it reaches the last customer to the northwest, the Wenatchee River County Park at Monitor.

The current system loses 40 to 60 percent of flow in unlined portions of the canal, according to a 2011 engineering report by Forsgren Associates, Wenatchee.

Kenneth Smekofske, a member of Pioneer Water Users Association, said the canal was also known as the Shotwell-Gunn Ditch. It was started by Harry Shotwell, his two brothers and their father, Jacob, but they ran out of money and brought Arthur Gunn, a banker, on board for financing to finish the project.

The ditch is the oldest irrigation system on the Wenatchee River if not the state, Smekofske said.