Salsipuedes Creek intersects with the Lower Pajaro River Basin in Watsonville, California. The Pajaro River Basin has suffered many flood events over the last century. In 1995, rising flood waters caused 95 million dollars in damage according to the US Army Corp of Engineers. The same report cites that over a billion dollars of property was at risk in the Pajaro Basin. The Santa Cruz County Department of Public Works was tasked with maintaining the levees that protect the city near the intersection of the river and Salsipuedes creek. They commissioned a geotechnical study published in April of 2002 to assess the condition of the levee adjacent to Watsonville.
The geotechnical engineering study reported details of piping failure, embankment slip out and excessive erosion. Rodent activity was a major cause of the piping failure. These failures were allowing an unacceptable level of lateral seepage which endangered the stability and integrity of the levee. After an exhaustive geotechnical evaluation that considered FEMA mapping and used the latest US Army Corp of Engineers computer modeling program, a vinyl sheet pile structure was chosen as the best solution. The geotechnical study states, “sheet piling will reduce piping, protect the outer embankment from uncontrolled seepage through the levee, and will reduce flow to acceptable levels.”
Hughes Construction began installing over 1000 ft of ShoreGuard® CL-9900 vinyl sheet piling after being awarded the job in June of 2002. Installation was successful using CMI’s PileClawTM mandrel attached to a hydraulic, ABI pile-driving machine. The sheets were driven at a rate of over 100 ft per day. The subsurface soils ranged from clayey silts to stiff clays. The project was finished ahead of schedule.
The engineering study concluded, “the most desirable (solution) is a cutoff wall that will not be impacted by rodent activity...and would require the least amount of maintenance.” Both steel and vinyl were considered as solutions. However, the steel thickness was specified after, as the report states, “considering and applying the applicable safety factors based on the corrosivity test results.” The required added thickness to meet these standards made steel cost prohibitive. Another consideration was the small work area “footprint” on top of the levee. CMI’s ShoreGuard® vinyl sheet piling works better than steel in small workspaces due to its lightweight and ease of handling characteristics. After 10 years of service and several floods, the Santa Cruz County supervisor of the project recently commented that they have had no problems, or related maintenance expenses since the ShoreGuard® sheets were installed.