Sherman Island Habitat Levee Setback Project

Phase II, Mayberry Slough Revegetation

Antioch, Ca
Fall 2008

Sherman Island is located in the Sacramento Delta area where the San Joaquin and Sacramento Rivers meet.  As part of the second phase of a habitat restoration project, Hanford ARC subcontracted to Wood Brothers, Inc. to perform the revegetation on a levee setback for Reclamation District No. 341.  The design by James C. Hanson involved construction of a setback levee, clearing of invasive vegetation, erosion control, and installation of approximately 2000 native plants.  Our contract included three years of maintenance and monitoring of the revegetation work. 

We mobilized as the excavation and grading work was completed in October 2008, to stabilize the exposed slopes.  Challenges included high winds, dense fog, tide cycles, and a compressed schedule.  Hanford ARC and Wood Bros carefully coordinated schedules, including night work to optimize efficiency and completely stabilize the project prior to the rainy season.

Erosion Control:  As the rough grading and rock installation on the new levee slopes were completed, Wood Bros. left a narrow bench of soil at the toe of the slope as a plug, which would then be used to backfill the key trench for the erosion control fabric.  Hanford ARC crews worked closely with Wood Bros. to install the erosion control fabric into the key trench, stapling it into place.  Approximately 12,000 square yards of coir fabric were installed on the levee slopes.

Rare Plant Salvage:  Mason’s lilaeopsis, a listed species in California, was present in several locations throughout the project site.  After a survey by LSA Associates mapped each location with GPS coordinates, Hanford ARC harvested clumps for replanting after the grading operations were complete.  Mason’s lilaeopsis grows in a very narrow elevation range, typically just above low tide.  Our experience on other projects has taught us the need to carefully locate these plants in conditions replicating the harvest site.  In this case we surveyed the existing elevations and replaced the plants at the same elevation on the new levee.  This required night work to access the planting area at a lower-low tide.

Revegetation:  The revegetation component included installation of approximately 2,000 plants and native seed along 5 planting zones on the new levee.  We harvested approximately 400 willow and mulefat cuttings from nearby DWR property.  For irrigation, we designed an overhead spray system charged by a pump drawing water from the adjacent slough.  Our three year maintenance contract includes weekly visits during the growing season and an annual monitoring report.