After heavy rains in Northern California, the side of a hill on the edge of a parking lot gave way, creating a sinkhole approximately 250 ft in diameter. This section of Wolf Creek directly at the bottom of the hole handles about one fourth of Grass Valley’s storm water drainage during the heavy season. After realizing there was a significant sinkhole issue, city engineers, contractors and Pacific Corrugated Pipe Co. worked together to create a solution.
Upon inspection, it was found that 20 to 30-ft trees had been sucked into the upslope opening of the culvert, creating a blockage. Engineers believed that this blockage is what caused the large sinkhole to form.
The existing culvert was 90 ft below the finished grade, so about 10,000 cu yards of dirt had to be excavated to expose the issue and take out the old pipe. The 39 ft of 72-in. pipe was used as a riser to connect the 150-ft of 90-in. pipe to Little Wolf Creek. One 45 degree elbow and one 90-in. by 72-in. tee was utilized to make the proper connection and ensure an effective solution for long-term stability in the area.
