Water Resources and Wetlands Restoration Projects
Hultgren – Tillis Engineers' water resources work has been primarily for levee districts, municipal improvement districts, conservation agencies, and private land owners. More than half of Hultgren – Tillis Engineers’ professional effort in recent years has been on flood protection infrastructure projects. Hultgren – Tillis Engineers personnel have provided engineering design and/or evaluation on 30 dams and hundreds of miles of levees and channels.
Delta Levee Rehabilitation (Sacramento-San Joaquin River Delta) - Hultgren – Tillis Engineers has undertaken geotechnical evaluations for hundreds of miles of flood control levees. Many of those levees have been in the Sacramento-San Joaquin Delta where, unlike upland levees, the levees continually retain water. These levees were constructed on weak peat and organic soil foundations. Hultgren – Tillis Engineers has become recognized as expert in evaluating the strength and deformation characteristics of organic soil foundations beneath Delta levees. One example is Reclamation District 830's levee on Jersey Island. As one of the Delta islands closest to the San Francisco Bay, the protection of Jersey Island is vital in protecting much of California's fresh water supply from salt water intrusion. The Reclamation District is undertaking a program to strengthen their levees and to bring the levee crest elevations up to the FEMA Hazard Mitigation Plan standards. To date, Hultgren – Tillis Engineers has assisted the District in improving more than 8 miles of the levee’s 15.5 mile perimeter.
Montezuma Wetlands (Solano County, CA) - Hultgren – Tillis Engineers conducted the stability and settlement analysis for a marsh restoration which involved raising existing ground surface grades to convert approximately 1,800 acres of reclaimed farmland into tidal and seasonal wetlands. The project site is located south of Fairfield and northeast of Suisun Bay, at the eastern edge of the Suisun Marsh. The Montezuma Wetlands project takes marine clays and silts dredged from harbors and channels and puts them to beneficial re-use to create tidal wetlands. Approximately 17 million cubic yards of sediment was used to raise the surface of the site to elevations suitable for tidal marsh restoration.
Emergency Rock Barriers (Sacramento–San Joaquin River Delta) - In early 2014, the Governor of California declared a drought State of Emergency and directed the Department of Water Resources to “take necessary actions to protect water quality and water supply in the Delta, including installation of temporary barriers”. Hultgren – Tillis Engineers evaluated geotechnical conditions at eight candidate locations for emergency rock barriers or tidal gates and provided design criteria for three rock barrier locations on Sutter Slough, Steamboat Slough, and West False River. The temporary barriers at Sutter Slough and Steamboat Slough will consist of rock barriers, while the temporary barrier at False River will consist of an integrated sheet pile wall and rock barrier solution.
Periodic Levee Inspection - Hultgren – Tillis Engineers performed periodic inspection for over 200 miles of levees and channels for the U.S. Army Corps of Engineers, Sacramento, Los Angeles, and Omaha Districts. See a separate category on this web page for brief descriptions of Hultgren – Tillis Engineers’ U.S. Army Corps of Engineers projects.
Delta Coves (Bethel Island, CA) - Hultgren – Tillis Engineers provided geotechnical engineering services for the local levee agency, Bethel Island Municipal Improvement District (BIMID), and for Contra Costa County. The project included constructing 3 miles of perimeter levees and interior peninsulas for residential 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. 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.