Las Gallinas Creek Levee Evaluation

Flood Zones od Marin County

In this photo, high tides in January 2006 approach the top of the wooden floodwall on the existing levee. Additional improvements to the levee are needed to afford greater reliability and address sea level rise.

The Las Gallinas Creek Levee Evaluation was a joint multi-year study of the Flood Control District and the U.S. Army Corps of Engineers to better understand the current condition and performance of the existing 2 miles of levees which help protect the Santa Venetia Community from flooding. The evaluation also sought to describe a set of possible preliminary alternatives which might help better protect the community from flooding, including those which addressed sea-level rise and provided a FEMA level of protection. Reports produced during the evaluation are available for review in the marinwatersheds.org library.

History


The Las Gallinas Creek levee protects Santa Venetia from inundation by tidewaters, which became a growing threat to the community as soils underneath it were compressed and the ground sank below sea level. Extensive flooding in the 1940s-1950s led to the creation of Zone 7 of the Marin County Flood Control and Water Conservation District (District). District funds built and improved levees and continue to do so. Five stormwater pump stations and various other flood control facilities were also constructed to work in concert with the levees and provide Santa Venetia with comprehensive flood protection.

Extensive breaching of the levees in the early-1980s inundated streets and homes with several feet of water. In response, redwood floodwalls were installed and continue to be maintained. These floodwalls increased the level of protection afforded by the levees by adding two feet to their height. Despite these enhancements, emerging issues and long-term improvement needs have been identified.

 

Needs


The last major improvements to the levees occurred over 25 years ago. Several needs must be addressed if the levees are to continue to protect Santa Venetia from flooding:

  • Levee heights must be raised to address their continued sinking and sea level rise.
  • The earthen fill (i.e., dirt) which makes up the levee must be maintained to provide adequate seepage protection and ensure their stability.
  • The wooden floodwalls, constructed 25 years ago, need to be replaced.

Solution


The levee has been the focus of an ongoing joint study headed by the District and the U.S. Army Corps of Engineers. Over $700,000 in combined federal, state, and county funds from outside of Zone 7 have already been committed to examine existing conditions and develop potential levee improvement alternatives. Local funds are required to continue the study and would ensure that matching outside funds (e.g., federal and state) can continue to be pursued.