Improving levees to meet FEMA certification
Improving Levees To Meet FEMA Certification
FEMA has instituted a nationwide plan for greater levee safety. FEMA is requiring that levees be certified as to their ability to provide protection from a 1 percent annual chance flood (meaning a flood that has a 1-in-100 chance of occurring within any given year). Levee certification is part of the FEMA Map Modernization (Map Mod) program to update flood maps and potential flood risk.
In 2007, the District began a process of evaluating all levees to determine their condition and the scope of repairs that may be required to achieve FEMA certification. A number of levees will require repairs to comply with FEMA’s new and more stringent guidelines. In some cases, new levees may need to be built.
Certification requires that levees meet certain standards, such as ensuring
- a 3 ft. minimum between the base—floodwater level—and the top of the levee (called freeboard);
- the levee is capable of withstanding certain water flow velocities, and wind and wave action;
- embankment slope and foundation protection are appropriate for the levee design and construction;
- soil conditions and other geotechnical factors that affect seepage are addressed;
- openings on closure devices are operational; and
- provisions are made for operations, maintenance, and periodic inspection.
In 2010, the District issued three contracts valued at $7.4 million to firms with the geotechnical expertise needed to continue levee studies in Zones 2, 3A, 4, 5, 6, and 12. To evaluate levees, the District has been conducting subsurface field exploration; performing soil testing, stability, and other technical analyses; and developing operations and maintenance plans. The final report on the status of levees in the six zones will be completed soon.
Ongoing Remedial Repairs
While levee evaluations are wrapping up, the District has provided FEMA with a levee remedial action plan to control seepage, repair erosion, and heighten floodwalls or embankments along several flood control channels.
Three large projects to improve levees along Alameda Creek in Union City were completed between 2010 and 2012.
- Phase One. Levees on both sides of Alameda Creek upstream of Ardenwood Boulevard were repaired to block seepage in summer 2010.
- Phase Two. In summer 2011, the south levee along Alameda Creek downstream of Ardenwood Boulevard was raised to provide freeboard and block seepage.
- Phase Three. In summer 2012, the toe of the north levee along Alameda Creek between the Union Pacific Railroad (UPRR) and Alvarado Boulevard was stabilized.
Two other major levee improvement projects raised the levee height to allow for greater freeboard and reinforce eroded levee embankments.
- The King and Lyons Creek levees in Fremont between I-880 and the slough to San Francisco Bay were completed in 2012.
- The south levee along Sulphur Creek between the Sulphur Creek Pump Station and the UPRR in Hayward was completed in 2013.