From the Trinity Journal:
Spring flows begin in ‘critically dry’ year
By AMY GITTELSOHN The Trinity Journal
This has been designated a “critically dry” year for the Trinity River, and a flow schedule has been approved reflecting that.
Last year the basin got the largest amount of water ever measured.
“This year is quite a bit different,” said Eric Peterson, data steward for the Trinity River Restoration Program, as plans were shared with the public April 12.
The critically dry determination is based on the April 1 forecast from the state Department of Water Resources for the water year running from October 2017 through September 2018. Based on factors including inflow to Trinity Lake so far and snowpack, that forecast estimates the full natural flow of the Trinity River at Lewiston for the year will be only 530,000 acre-feet of water. A normal water year is approximately 1.1 million acre-feet and last year was more than double the normal amount.
Full natural flow is the amount of water that would pass through Lewiston if not for the dams.
In a critically dry year, 369,000 acre-feet of water is to be released to the river under the 2000 Trinity River Record of Decision.
There will still be a high spring flow with several peaks, and the release from Lewiston Dam has started ramping up. The highest peak is to be a release of 1,900 cubic feet per second on May 13.
During the spring high flow, the restoration program usually adds gravel at points below Lewiston Dam to compensate for gravel not getting into the system due to the dams. Program staff say this adds complexity to the river to provide habitat for different life stages of the fish, with shallow areas, deep spots and eddies.
However, in this critically dry year no gravel is to be added.
Restoration program staff explained the flow hydrograph, which includes several peaks.
Objectives include flow and temperatures for juvenile and adult salmonids, providing diverse fish habitats, getting macroinvertebrate “bugs” that fish eat into the water and enabling a study of macroinvertebrate drift, moving fine sediments, delaying Foothill yellow-legged frog breeding until after the flow peak, distributing chinook fingerlings released from the Trinity Hatchery and discouraging riparian growth in the channel.
The presentation also included information regarding the increases of outgoing juvenile chinook salmon since the restoration program started.
Peterson said the 2012 adult return was very good, and since then the warm ocean current has caused poor conditions. However, he noted that the smolt numbers since 2014 are still well above the 1990s.
Asked if the ocean change is cyclical or due to global warming, fisheries biologist Todd Buxton said a natural cycle and global warming are involved, and all of the Pacific Rim chinook salmon populations are having a hard time.
One good sign, he added, is that a higher proportion of early-returning “Jacks” than expected returned last year. That is good news in the short-term, he said, but long-term he didn’t speculate.
Asked if the program is taking away what adult fish need to provide for juveniles, Peterson responded that program staff are trying to provide for both, but “we don’t get big ones if we don’t have little ones to start with.”