Inyo County flash floods and fish kills
On Tuesday, Aug. 6, Los Angeles Department of Water and Power (LADWP) Water Resources Manager Brian Tillemans addressed the Inyo County Board of Supervisors to clarify what part the DWP had to play in the death of an estimated 400-600 fish in the Owens River below the Alabama Gates spillway during the week of July 22.
The DWP was undertaking scheduled maintenance to repair the walls of the aqueduct about one mile south of the Alabama Gates, and had temporarily shut off the flow of water through the aqueduct to allow crew and equipment access to about 250 yards of the aqueduct, Tillemans said. Because of the low runoff, he said, “This was an ideal time to get the work done.”
When the rain began to fall, however, the DWP quickly realized it had a crisis on hand. “We had good pre-planning, but you can’t plan for flash floods,” Tillemans said. The ensuing flash floods, which washed across U.S. 395 and caused an estimated $1.3 million in damage to Inyo County roads alone, flooded down creeks at the base of the mountains into the aqueduct.
The DWP took immediate steps to protect both men and equipment, spreading floodwaters onto the alluvial fans at the foot of the mountains to the west and releasing flows from the aqueduct, some onto leasee’s lots, granting an extra boon of water. Part of this release involved the opening of the Alabama Gates spillway, which discharged water underneath 395 and into the Owens River. The release went on for four days, from July 22-25. In total the DWP released 470 acre-feet of water into the Lower Owens River, said Inyo County Water Department Director Bob Harrington.
Harrington explained to the Board that he became aware of the event on July 23, when a member of the public called to express concern. On Friday, July 26 he said, the Lone Pine tribe notified Harrington of their own concern about the quality of water being released into the river, observing dead fish and a strong odor of hydrogen sulfide. Both the DWP and Water Department assessed the damage, and found an estimated 400-600 fish dead at the Owens Lake pump-back station eight or nine miles south of the Alabama Gates.
Harrington explained that it was the high volume of water that killed the fish. The water stirred up organic sediment in the river, which starved the river of oxygen. This is already a sensitive time for the fish, Harrington explained, because the water is warmest at this time of year, and oxygen is less soluble in warm water.
Harrington noted that the Water Department has previously expressed concerns about the water quality in the portion of the river below the Alabama Gates, “Because it doesn’t receive as much effect from the seasonal habitat flow as the section above the Gates,” he said. In the wake of the fish kill, he said, the Water Department will now be working with the DWP to address these concerns.
Supervisors questioned why the DWP had notified neither the Water Department nor the County about the impact of flash flooding to the aqueduct. “A courtesy notification may have helped in this case,” said Supervisor Rick Pucci. Tillemans agreed. “When we’re starting to get these kinds of waters we need to notify everybody, including the County,” he said.
Tillemans also related some of the greater damage sustained by the DWP during the event, such as Shepherd Creek and other base measurement stations blowing out, and significant damage to the Division Creek power plant. “God knows when that’s going to be up,” he said.
Looking at the glass half full, however, Tillemans noted that “We did get a good flushing flow in the Lower Owens.”
The Board agreed that the event could have been worse. Supervisor Linda Arcularius called the flash flooding “an extraordinary situation; it sounds like Mother Nature had a role that all the planning in the world might not have anticipated.” Yet Harrington argued that not all the blame rests on Mother Nature, as it was the combination of the DWP maintenance work and the flooding that led to the fish kill. “There was more to it than just the rain, but the DWP really couldn’t avoid what happened,” he said. “It doesn’t appear to be that the entire fishery was decimated,” he added. And if the fish population doesn’t come back on its own, he said, the DWP may mitigate by restocking.
