Hultgren-Tillis Engineers

Representative Projects: Dams & Levees :

Delta Coves Project, Bethel Island, CA - The project included construction of about 3 miles of perimeter levees and interior peninsulas for building pads within the interior of Bethel Island. The new levees connect to the existing levee where a 300 feet wide section of the existing levee was removed to inundate about 300 acres of land.  A deep lagoon extending up to 35 feet below the levee crest was created as part of the project.  The levee is constructed with material predominately silty sand from within the project site.  Earthwork for the project included about 5 million cubic yards of excavation. 

A 3-mile long, 50-feet-deep soil-bentonite cutoff wall extends from near the levee crest, through the foundation sand and into the underlying clay to protect adjacent properties from seepage.   The project included a seepage control system, about 1 mile in length that is adjusted through 15 separate weirs and monitored by more than 40 piezometers.  The project included two dual-sheetpile structures connected by tie rods where the new levee connects with the existing levee.  Potentially liquefiable sand was densified using deep dynamic compaction and stone columns.  Hultgren-Tillis Engineers provided geotechnical engineering services for the local levee agency, Bethel Island Municipal Improvement District, and for Contra Costa County.