Friant Water Authority announces the completion of Deer Creek siphon on Friant-Kern Canal, which prevents canal overflow, flooding
TULARE COUNTY – The project to address flooding and subsidence in the Friant-Kern Canal hit a milestone with the recent completion of a critical siphon structure, sparing surrounding areas of flood damage in the event of heavy rainfall.
In November, the Friant Water Authority (FWA) made a key accomplishment on their 33-mile middle reach project that has plagued conveyance on the Friant-Kern Canal (FKC). Aptly named the Deer Creek siphon, the siphon ensures the FKC can handle high flows in the event of potential winter storms or flood events by allowing water from the canal to pass under the creek.
“Without dams or other flood management features to attenuate flows, a large winter storm could have overwhelmed the creek and caused widespread flooding at the construction site and nearby farms,” FWA stated via Waterline newsletter.
The subsidence, which causes the ground of the canal to sink, was brought on by groundwater overdraft conditions that occurred during the California 2011-2019 drought. Although dry for majority of the year, the creek can quickly overrun with water during storms, leaving the channel and its flows uncontrolled, according to FWA. With the Deer Creek siphon, water will be carried under the creek, preventing overflow and flooding in nearby communities. The completed structure includes two turnouts, a concrete-block recorder house, a wasteway, a check structure and a siphon inlet and outlet to allow water to pass without flooding the creek.
Deer Creek is a water source that runs through Terra Bella, a small community south of Porterville. The creek passes through the Avenue 104 and Road 208 intersection and is in the northernmost section of the Middle Reach of the Friant-Kern Canal. According to a FWA 2019 report, the area most impacted by subsidence is between the Tule River and Lake Woollomes, particularly in the area of Deer Creek.
However, according to FWA, the middle reach project construction team worked hard to address the subsidence issues with Deer Creek by December. This was to ensure that in the fortunate event of a wet winter, high flows would not endanger project construction or surrounding areas.
“The team continues to make swift progress on the rest of the middle reach and as of [December], they estimate that the project is approximately 50% complete and still on track to wrap up in January 2024,” FWA stated via Waterline newsletter.
According to FWA, the water authority discovered a problem with land subsidence affecting the Friant-Kern Canal in early 2017. This involved the canal’s carrying capacity and its ability to deliver water to Friant contractors towards the southern section of the canal. This is not a new problem, however; according to FWA, the Friant-Kern Canal’s carrying capacity has been compromised by various factors – including subsidence – since it first began operation in 1951.
During a storm in December 1966, Deer Creek crossing had peak flows recorded at 10,100 cubic feet per second, according to FWA. This was nearly double the capacity of the Friant-Kern Canal at its outlet, Millerton Lake, which is about 15 miles north of downtown Fresno. During the time of that flood, the headwaters of the Deer Creek basin received more than 30 inches of rain in less than one week. The Friant-Kern Canal was heavily damaged when the creek’s ponded floodwater, which is a circumstance when rainwater overwhelms a water system with more water than can be stored, broke into the canal. This damaged the canal’s concrete lining and allowed roughly 100,000 cubic yards of mud and debris to fill the canal for more than 10 miles downstream. Additionally, approximately 3,000 nearby acres of productive land were flooded.
In the past, water managers were able to manipulate canal operations to help reduce circumstances of lost water capacity. However, the problem that emerged in 2017 is enhanced by rapid, severe land subsidence in the Corcoran and Tulare Basin areas, which are adjacent to the Friant-Kern Canal near Deer Creek. In 2015 to 2016, land elevations dropped by two feet near Corcoran, a town 18 miles east of Porterville. With this amount of subsidence, there is no way to operate the canal that would eliminate the impact of the subsidence on water users.
The Friant-Kern Canal Middle Reach Capacity Correction Project is a joint effort between the FWA and the Bureau of Reclamation (Reclamation). According to the Reclamation, the Friant-Kern Canal delivers water to about one million acres of some of the most productive farmland in the country. It also provides drinking water to thousands of San Joaquin Valley residents. In order to address the canal’s capacity loss, the Reclamation and FWA implemented the project, which first underwent construction in January 2022.