The slow seepage of water from the San Justo Reservoir off Union
Road has saturated the soil on its perimeter and caused landslides
that the San Benito County Water District hopes to curtail by
modifying the amount of water stored there.
The slow seepage of water from the San Justo Reservoir off Union Road has saturated the soil on its perimeter and caused landslides that the San Benito County Water District hopes to curtail by modifying the amount of water stored there.
“In the beginning years after the reservoir was built (in 1987) the landslides weren’t as much of a problem,” said Jeff Cattaneo, director of the water district. “When it was built they identified those areas and put liner in to minimize the amount of water that would seep out. Once the reservoir was filled, they recognized seepage was greater than anticipated and landslides developed from water saturating the soil.”
Until three to four years ago, he noted, the landslides were “increasing in size and severity” until extra liner was added and return wells were installed to “de-water” the hillsides to slow the intrusion of water.
At that time, the Bureau of Reclamation required that the water district lower the surface elevation of water in the reservoir to 485 feet from 500 feet to slow the amount of seepage.
“It has been fairly effective at reducing the landslide issues,” Cattaneo said. “We believe that part of the problem is that the reservoir was held at the 500-foot mark for so many years – it was almost always full – that it created an equilibrium where water in the soil was very high, which exacerbated the slide issues.”
Instead of spending the estimated $3 million to $10 million it would take to repair the reservoir, the district recently hired a consultant to develop a plan to alternate the water storage throughout the year in an effort to moderate the seepage of water.
“We’re proposing to Reclamation, in an effort to regain the 2,600-acre-feet of water that we lost (by reducing the maximum capacity), that we return to operating it much like we did in the early years: filling it early in the season to maximize storage for agricultural deliveries, then draw it back down to 485 feet and below during the growing season,” Cattaneo said. “Then we’d raise it back up in the winter period just before the growing season starts again.”
He said the state has “been receptive to that proposal,” which will include studies and additional monitoring to ensure its effectiveness. The cost of that plan is expected to approach $750,000.
“We’re optimistic the reservoir re-operation plan will return most of the utility of the reservoir to us and return 2,600 acre-feet of volume.”
See the full story in the Pinnacle on Friday.
