Some critics believe and even root for a Sky Is Falling curse on High Speed Rail referencing all their recent troubles,false steps and delays. It turns out however, that Chicken Little need not bother looking to the heavens but better watch out down below.
Geotechnical studies along the proposed high speed rail route through Fresno and Madera counties northwest of Fresno have found that the ground has collapsed 18 inches since 2011 when monument markers where placed by CHSRA engineers to study land subsidence. The problem is caused by farmer’s heavy groundwater pumping in the region.
This is another news nugget from the most recent URS Corp regional consultants’ CHSRA Progress Report dated Aug 14. (They are the RC in the paragraph below -PMT is the Project Management Team.)
The report says ” The potential for ground subsidence as a result of groundwater extraction and oil extraction was raised in the FB geotechnical reports, and its potential impacts on the FB HST structures are being discussed with the EMT. The RC has identified subsidence as a project risk, and considers this a program-wide issue that affects several HST segments and that may influence the choice of HST infrastructure, such as trackform. This information was expanded in the revised Draft Geotechnical and Seismic Hazard Report issued on April 19, 2013. Recent survey of the existing Authority monuments indicated up to 18 inches of settlement since their installation circa 2011, as well as some lateral movement. The RC and PMT met with Caltrans on July 26, 2013, to discuss settlement issues on their infrastructure within the FB section. Caltrans has noted the subsidence issue, but has not had to undertake repairs to their facilities in the Central Valley as a result of subsidence.”
Subsidence issues are reverberating across a wide swath of the Valley’s economy impacting water, ag,construction, public budgets and political spheres. Among other unsuspected twists are accelerating subsidence is impacting the federal effort to restore the San Joaquin River and its wildlife as well as flood control capacity because of reduced carrying capacity of the San Joaquin River channel.
Ironically it has been farmer opposition to the construction of the rail system through their farms that has been the most vocal.Now as it turns out -their overpumping may literally pull the rug out from the high speed rail track – and their own future as well.
Need To Solve Issue
High speed rail builders in China face the same issue as outlined in this 2011 story.
“The land subsidence also has consequences for China’s prized high-speed railways. The Beijng-Tianjin, Beijing-Shenyang and Beijing-Tanggu high-speed lines run across land subsidence areas. Taiwan’s high-speed rail crisis serves as a direct lesson. The rail system, which cost NT$500 billion, might be forced to close in 10 years if the land subsidence problem cannot be solved.
According to the design of the Beijing-Shanghai high speed railway, which runs at a speed of 300 kilometers per hour, the land subsidence cannot exceed 5 millimeters over 100 years. As the railway runs across the world’s largest land subsidence area, it raised high demands for early designs and later subsidence monitoring.”
A Sierra2theSea story earlier this year highlights where perhaps the worst of the problem lies – south of Hwy 152 near Dos Palos.Here is an excerpt.
A 28 Ft Ripple Effect
There is a growing ripple effect on the San Joaquin River flow capacity due to vigorous groundwater pumping in one part of the Valley – in Madera County. The land below some farmers feet is sinking and sinking faster and the implications resonate far and wide.
Land adjacent and just east of the San Joaquin River between Dos Palos and Los Banos is sinking at an accelerated rate new state studies have found. So says Chris White,manager for Central Valley Irrigation District who told his findings to a meeting of Associated California Water Agencies (ACWA) in Fresno last week.
Survey work on the San Joaquin River as part of the Bureau of Reclamation restoration process in 2010 found land subsidence in this area of nearly 2ft compared to benchmark survey done in 2008.
White says a dramatic illustration of the drop came when a farmer last July texted him a photo of his well casing that had been painted a bright color down to ground level a few years earlier but now was unpainted a good 18 inches from the ground.”What’s going on here” asked the farmer?
It wasn’t gophers. More like an episode of ’Honey, I Sunk The Farm.’
“If this problem is left unchecked it is possible to see land subsidence of 28 feet or more.” Did he say 28 feet?
A famous photo shot near Mendota in 1977 shows just how much Valley farm land sunk from 1925 to 1977 which was about 28 ft according to a USGS study.
Just what impacts land subsidence could have on the tracks along Hwy 152 as it swings away from Hwy 99 toward the Bay Area remain in question.