Subsidence Lowers Friant–Kern Canal by 5 Inches in 5 Months

LINDSAY, CALIFORNIA  -  When officials with the Friant Water Authority (FWA) did an initial survey in April 2017 to measure subsidence along the Friant-Kern Canal, they expected to see impacts from the recent drought. What they measured in some places was a nearly three foot drop in the canal elevation. 

Even with last winter’s record breaking rain, snowfall and runoff, they assumed the discouraging trend would continue. What they found in early August when they resurveyed portions of the canal confirmed their fears. Since April the canal has dropped another 5 inches in one particularly hard hit location. 

“These findings are not entirely unexpected,” commented Doug DeFlitch, Chief Operating Officer for FWA. “Subsidence is a long-term challenge for the Friant Division, and will not be remedied after one year of good rain.” 

Jason Phillips, Chief Executive Officer for FWA added, “The continuing subsidence issue is why FWA is exploring possible funding mechanisms for bringing the Friant-Kern Canal back to its designed operational potential. A fully functioning canal will help achieve the groundwater/surface water balance the Friant-Kern Canal was designed to maintain, and lessen the impacts of subsidence.” 

PR - Five Inch Drop at Friant Kern Canal Since April - 11-29-2017-2.jpg
PR - Five Inch Drop at Friant Kern Canal Since April - 11-29-2017.jpg

Land subsidence is the gradual sinking of an area of land which occurs more dramatically in the region when groundwater is over drafted. Water that is removed from very fine clay-like pore space in the subsurface no longer has its internal strength and over time compresses and the surface of the land drops. During the drought when surface water supplies were limited or unavailable, regional farmers, cities and others relying on surface water supplies turned to groundwater. The resulting subsidence forced cuts in water deliveries to parts of the canal system during critical times this past summer.

The Friant Division was designed to bring stability to the San Joaquin Valley’s groundwater supply, which was threatened at the beginning of the 1920s by decades of groundwater pumping. The Friant Division’s two canals – the Friant-Kern and the Madera – source high-quality surface water from the San Joaquin River that supports crops, cities, and groundwater recharge. This investment to establish the Friant Division has paid off by providing stable surface and groundwater supplies that created and sustain a world-class agricultural sector that in turn supports numerous communities and businesses. 

The Friant-Kern Canal is a gravity-fed facility and currently does not rely on pumps to move water. Subsidence disrupts the natural grade line, which negatively affects the canal’s ability to convey water. As the surface expression of land subsidence continues to occur, the canal will continue to lose capacity. Current estimates put those reductions at nearly 60% of design. 

FWA is a joint-powers authority formed in 2004 by a majority of the water agencies receiving water from the Friant Division of the Central Valley Project. Its primary purposes are to operate and maintain the Friant-Kern Canal and to serve the information and representation needs of its member agencies.