Restoring Stability: Oakdale Irrigation District Tunnel Rehabilitation

Nordby Wine Caves recently partnered with Njirich & Sons, Inc., to rehabilitate Oakdale Irrigation District (OID) Tunnels 3 and 4, located northeast of Oakdale, California. OID has delivered irrigation water to 55,000 acres of farmland in the Central Valley for more than a century.

Constructed in the early 1900s, Tunnels 3 and 4 needed significant repairs to restore stability and improve water flow efficiency. Collectively spanning about 2,250 feet, the 8-to-20-foot tunnels were originally built without lining or ground support, leaving them vulnerable to erosion and structural degradation. Erosion had caused stress fractures, ground instability, and flattened tunnel crowns. To address its aged infrastructure, OID developed a Water Resources Plan (WRP) to modernize and rebuild its system to meet the needs of its changing customer base.

Nordby Wine Caves widened and reshaped the tunnels to an arch shape to improve stability of the tunnel ground and increase flow rate capacity. We incorporated shotcrete tunnel lining and cast-in-place concrete inverts to further prevent erosion and improve stability and water flow capacity.

Another key project component involved reinforcing the portal cutslopes, the sloped surfaces leading into the tunnels. Left unprotected, they were prone to erosion from water runoff which poses long-term structural risks. Our team lined and stabilized the cutslopes for additional support to withstand the area’s fluctuating water levels.

Despite a tight four-month construction window limited to the off-season for irrigation, Nordby Wine Caves executed and completed the tunnel update with precision. The construction process included close collaboration with project partners to ensure that the new design would not only restore tunnel integrity but also increase flow efficiency, safeguarding the region’s water distribution system for years to come.

Photo credit: Provost & Pritchard Consulting Group