The city of Morgan Hill in Santa Clara County sits at the southern tip of Silicon Valley. The city is home to several high-tech companies and has attracted upscale residents for dining, shopping, wineries and outdoor pursuits.
Graniterock photo
While many California cities don't get enough water, Morgan Hill sometimes gets too much. Fed by a multitude of tributaries and reservoirs, Llagas Creek often swells during significant rains, resulting in damaging floods to the nearby communities.
The Santa Clara Valley Water District designed a project to help control Llagas Creek. Valley Water called on Graniterock, headquartered in Watsonville, to handle construction.
Graniterock's work will protect the area from 100-year flood levels.
A key element of the effort includes widening a 6.5-mi. stretch of the creek by removing an estimated 720,000 cu. yds. of dirt and rock. Project leaders believe this piece of the job will keep excavators, bulldozers and trucks in action for some time. The effort will cost $129 million, with Phase 2B considered one of the top flood protection projects in the nation.
The construction team also will reroute some of the tributaries to reduce their flow as well as to allow for the construction of a massive double box culvert in the city limits of Morgan Hill. When completed, the Llagas Creek Flood Protection Project will protect more than 1,000 homes, 500 businesses and 1,300 acres of agricultural land.
The Graniterock project management team includes project engineers Josh Cutler and Gio Giannotta and senior project managers Dave Olivas and Jim Mitchell. Because the box culvert will be in an already built-out city, workers will construct it underground instead of in the traditional manner of cut and cover precast box culverts.
Much like building an underwater highway for water, the construction team began the early phases of the work with extensive rerouting of utilities, sewer lines and other pieces of infrastructure. The team carefully selected which types of equipment to use, considering the presence of overhead power lines and other restrictions.
Construction teams have begun the work by digging a hole approximately 15 ft. deep and setting up the shoring system to keep the walls safe for work. Carpenters were next in building the false works for concrete pouring and positioning rebar.
Graniterock photo
The completed box culvert intake will be 10 ft. by 9 ft. Construction of this box culvert will cost approximately $30 million and require several million pounds of steel. The box culvert will replace and improve the city's storm drainage system.
Next year, the project team will construct another set of box culverts. It will be composed of two 10-ft. by 9-ft. cells.
"This work will greatly improve our environment," Cutler said. "In addition, some of the dirt and rock that is excavated will be used to reclaim an old mining pit near Hollister. That will enable us to restore the site close to its original level."
The work will require serious equipment muscle to control the water and bring safety to the community:
• John Deere 470 GLC excavator
• John Deere 850 dozer
• Cat D8 dozer
• 80-ton crane with vibratory head
• 40-ton crane used for assembling other cranes
• 250-ton crane used for lifts
• Water trucks for dust control
• More than 50 haul trucks
Graniterock photo
"Often, we have had as many as 400 loads of dirt leave the work sites in a day," Cutler said. "In addition to truck drivers, we average 70 workers daily on the site."
The project is like Graniterock's previous job built for Santa Clara Valley Water at Llagas Creek in 2020. The Morgan Hill project is more challenging because of its location in downtown Morgan Hill.
The project's lead estimator, Randy Bonino, is a huge fan of the project after seeing the damage from winter floods in the area.
"I've been going to public meetings about this for years," he said. "I care about this project because it's in my backyard, and it's only a matter of time before the creek floods again." CEG
