By Deb Murphy
Three hundred acres scarred by lost meadow grasses in the Five Bridges area, north of Bishop, south of the Owens River, could be the poster child for failed mitigation of groundwater pumping. The mantra — if there is damage, it will be mitigated — has not worked at Five Bridges.
The water table dropped after a year-and-a-half of pumping; twenty-eight years later the damage has not been reversed.
Thirty six local water-watchers got a first-hand look last Wednesday during a Water Commission field trip.
Interest in the mitigation efforts spiked after Los Angeles Department of Water and Power opted to re-tool and re-activate two wells used to dewater the gravel pits to the north and send water through the aqueduct system in the late 1980s.
Those wells, W385 and W386, ran for approximately 18 months before the damage was identified by an Inyo County Water Department staffer during a fly-over. The wells were “permanently shut down,” a status disputed by LADWP. The Department has retrofitted the wells to limit pumping to depths between 350-500 feet and will be doing a California Environmental Quality Act analysis on impacts.
ICWD hydrologist Keith Rainville explained the geology of the area at the first stop of the field trip, pointing out the natural flood plain and series of terraces, dotted with sage, within the 300 acre site. The group moved on to get a look at the damaged area as well as monitoring wells used to gauge water table levels.
Five Bridges is a revegetation project, as opposed to far simpler re-greening mitigation. The goal is to restore communities of native species, the toughest of which are meadow grasses dependent on a high water table.
The Technical Group, made up of LADWP and County Water Department staff, agreed to some objectives including species composition, according to ICWD Director Bob Harrington. “The site has a hard time maintaining those objectives,” he said. “At times it has gotten up to (the objectives) of species composition, but now it’s far below.”
The past four years of drought hasn’t helped. But up and down the valley, areas impacted by groundwater pumping have fared worse than those not impacted.
Mitigation efforts included rain guns, water spreading, irrigation through channels and weed control including herbicides that also impacted native meadow grasses. But the invasive pepperweed prevails and the Owens Valley Checkerbloom, endemic to the area, seems to have disappeared.
The history of the Mitigation Plan for Five Bridges is vague. Plans have been developed but not officially approved by the Tech Group. Late last month, LADWP released a new draft plan.
Initially, high Owens River flows spread water over the low-lying valley areas at Five Bridges. In 2000, water was released into the area through a C Drain that runs from the Bishop Canal to the Owens River.
According to the 2016 draft plan, “river flows were no longer feasible in the Owens River system due to reductions in exports from the Mono Basin.” The plan calls for diversions “to improve efficiency of water spreading by directing it to areas that have not been irrigated for some time due to channelization.”
In addition to flow management, the draft plan calls for broadcasting native seed in areas with low coverage, additional research on weed eradication and the hope that native species seeds “may flourish with more efficient water spreading.”
The enormity of mitigating damage was anticipated in the 1991 Environmental Impact Report. “Even if water management were to revert to pre-project (the second aqueduct) operations, the affected vegetation could require a time period of many decades to return to the pre-1970 conditions.”