Lower Tubbs Island/Tolay Creek Marsh Enhancement

Sonoma County, Ca 

Audubon California/San Pablo Bay NWR
Fall 2009

Historically, Lower Tubbs Island was managed for duck hunting with levees, berms, tide gates and drainage channels to control tidal influence.  In 1978 San Pablo Bay NWR refuge acquired the land and began to plan for enhancement and restoration of a more natural tidal marsh.  The project we constructed in the fall 0f 2009 included several goals, based in improving connectivity to the adjacent baylands to increase the tidal prism within Tubbs Island.

We contracted with Audubon California to implement the design by Wetlands and Water Resources.  The project was divided into three distinct areas of the island, each involving channel construction to connect ponded areas to active tidal channels.  The new channels are designed to replicate natural tidal channels. 

We used low ground pressure (LGP <4 psi) equipment including excavators, bulldozers and tracked dump trucks, and worked from crane mats for the actual channel excavation.

Area 1:  included excavation of three new channels and enlargement of an existing channel to increase drainage of several ponded areas.  The approximate 360 CY generated was used to fill several low areas, to address ponding at those sites.  Also, we used the soil to repair eroded areas on the levee to be retained.

Area 2:  included four breaches of an interior berm to increase connectivity to several ponded areas.  We excavated two new channels and enlarged several existing channels to feed the berm breaches.  Lastly, we excavated a new channel from the end of the existing borrow ditch through the marsh, to connect the Tubbs Island northern tidal channel to the northern borrow ditch increasing tidal exchange.  This excavation produced 1,065 CY of soil which we placed in low-lying areas of the marsh plain to reduce ponding, and repaired eroded areas of a levee to be retained.

Area 3:  had no existing channels connecting it to a tidal source.  Marin-Sonoma Mosquito and Vector Control District cut a new channel approximately 1000 feet long, on the western side of the borrow ditch.  We then breached the levee at the northern end of this excavation and created a small connector channel to drain the adjacent ponded area into the new channel and the breach.