System failed in 2014 mudslide

By Marcy Stamper

After eight months of meetings among irrigators, property owners, hydrologists, engineers and fish biologists to deal with the effect of floods and mudslides in the Benson Creek watershed, the group is close to a resolution to fix the damaged irrigation system.

The group may also study the hydrology of the larger watershed next year.

The Benson Creek Watershed Group has been meeting with representatives of the Washington Department of Fish and Wildlife (WDFW), the Department of Ecology and the Okanogan Conservation District to try to address issues caused after several dams in the upper watershed failed in a heavy rainstorm two years ago, flooding roads and farms and destroying the irrigation infrastructure.

The affected parties have been weighing two main goals — repairing the irrigation system and restoring the system of lakes and streams to provide year-round flows in Benson Creek, said Terri Williams, a conservation planner with the Okanogan Conservation District, who has been facilitating the discussions.

The group has decided to rebuild the irrigation system to provide water to the nine parcels in the private water-users’ group. The work would be partially supported by grants for agriculture, said Williams. There are three or four members in the water-users’ group, who farm a total of nine parcels.

Future analysis

In addition, WDFW and Ecology are considering funding an in-depth analysis of the hydrology of the area to see if it has the potential to support year-round flows and create fish habitat in Benson Creek, which runs into the Methow River. That assessment would not be done until next year at the earliest, in part because there is not enough money to do a study now, said Williams.

All the participants agreed that the first priority is fixing the irrigation system, since the farmers have spent the past two summers without water, said Williams. That involves replacing a pipeline, repairing the settling pond, and doing some dredging so that the intact lakes that feed the system can hold more water. Increased capacity in the lakes could also help protect against future floods, said Williams.

Earlier this year, WDFW repaired the spillway at Chalfa Dam (also called Wenner Lake), the highest of what had been a string of five lakes in the watershed. Two of the five lakes filled with sediment and are being allowed to become wetlands. A privately owned lake has been restored and the spillway on the lowest lake will be repaired as part of the irrigation fix, said Williams.

The system failed in August 2014 after heavy rains caused erosion on steep slopes above Chalfa Dam. The area burned that summer in the Carlton Complex Fire, leaving little vegetation to hold soil and sending a torrent of water and debris down the hillside and onto private property along Benson Creek Road in the August rainstorm.

The flood has also deposited a lot of sediment on some fields, where the creek has spread out in new channels. Assessing and tackling that situation is proving more complex than the other issues, said Williams.

The conservation district is still confirming funding for the irrigation repair but expects the work can be done this fall, said Williams.