Featured Projects — Modeling Prospect Island Tidal Restoration Modeling

The 2008 U.S. Fish and Wildlife Service Biological Opinion on the Coordinated Operations of the Central Valley Project and State Water Project requires the California Department of Water Resources (DWR) to restore 8,000 acres of intertidal and associated subtidal habitat in the Sacramento–San Joaquin River Delta and Suisun Marsh in order to improve habitat conditions for delta smelt. With the Prospect Island Tidal Restoration Project, DWR is planning to restore approximately 1,600 acres of tidal marsh and associated aquatic habitat within Prospect Island.

In collaboration with Wetlands and Water Resources, Inc. and Stillwater Sciences, RMA was contracted to perform hydrodynamic and water quality simulations to assess the benefits and potential negative impacts associated with different Prospect Island restoration alternatives. Restoration alternatives differed primarily in the placement and number of levee breaches to adjacent channels. To perform this work, RMA refined our Bay-Delta Model grid around the project area and revisited our hydrodynamic, salinity, temperature, and particle tracking model calibrations with an emphasis on the North Delta region.

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Map of average particle exposure times within Prospect Island for a restoration alternative with a breach to Miner Slough.

Hydrodynamic and water quality simulations were performed on over 15 different restoration configurations to identify alternatives that maximized benefits, including:

  • Generation of on-site phytoplankton biomass
  • Export of phytoplankton to important juvenile fish rearing areas

And minimized potential negative impacts, including:

  • Scour potential to Ryer Island levees
  • Tidal range reductions
  • Sacramento Deep Water Ship Channel cross-current velocity increases
  • Temperature increases in adjacent water bodies
  • Violations of D-1641 Delta salinity standards

Results and benefits

Analysis results were used by DWR managers, in consideration with additional modeling study results and operational constraints, to select an alternative configuration for the tidal restoration. The Prospect Island Tidal Restoration Project is currently in the California Environmental Quality Act (CEQA) permitting phase, with planned construction beginning in early 2016.

As part of the Prospect Island restoration modeling work, RMA participated in a series of workshops held by the Delta Regional Ecosystem Restoration Implementation Plan (DRERIP) working group. Presentations of modeling results were given to the working group, and RMA helped set in place some of the procedures and expectations for numerical modeling of tidal marsh restorations that will be used for future DWR projects related to the Biological Opinion.