Parsons Slough Project Monitoring
The parsons sill project was successfully completed, the first project that will reduce tidal erosion in the estuary, and everything is going as expected. In response to questions about the Parsons Slough Project monitoring, we have posted two reports. One is an updated Parsons Slough Adaptive Management Plan, and the other is the 2014 Parsons Slough Project Annual Report (1.5MB) on the Parson monitoring submitted to the RWQCB and USACE. The Parsons Slough Adaptive Management Plan was developed collaboratively with smaller working groups composed of teams of scientists and resources agency personnel. They focused on identifying areas of positive and potential negative outcomes of the sill and developed monitoring strategies to identify changes. Under each objective is a brief summary of the outcomes to date. The areas of focus include: hydrodynamics and geomorphology, water quality, habitats, fish, invertebrates, waterbirds, and marine mammals.

Elkhorn Slough Restoration Project Completed

After four years of work and input from more than one hundred scientists, specialists, and lawmakers, the Parsons Slough Project is complete.  This project, funded through the American Recovery and Reinvestment Act and managed by the Tidal Wetland Project—a joint effort between the Elkhorn Slough National Estuarine Research Reserve (ESNERR), was the most efficient and lowest risk approach to reducing erosion and wetland loss in Elkhorn Slough.

The construction of an underwater sill – 200 feet wide, 10 to 15 feet tall and five feet under water – started on November 10, 2010 and was completed on time in February of this year.  The sill acts as an underwater barrier to slow the flow of the tide and reduce erosion.  The finishing touches – repaving the staging area at Kirby Park and leaving behind a dock for public use – were completed in early May.

Early monitoring of the sill indicates the project is a success. The sill is expected to significantly reduce the erosive tides in Elkhorn Slough and prevent thousands of cubic yards of sediment from washing into the bay each year.  The cost to replace that sediment by other means would have cost hundreds of thousands of dollars annually.  The project is anticipated to restore an additional seven acres of tidal marsh around the perimeter of the Parsons Slough Complex.

Elkhorn Slough otter raftConstruction monitoring wrapped up in late March, and the data indicates that the plant, bird, and other animal life that inhabit this unique environment have adapted well to the project.   Monitors have already sighted as many as five otter moms and pups resting in the area by the sill, and witnessed another otter being born very near the construction site this April.  Harbor seals with pups are also using the area extensively. Long term monitoring of the wildlife and habitats in the area will continue for years to maximize the opportunity to learn about the project.

The Parsons Slough project not only improved habitat and reduced a major ecological concern in the slough, it has created or saved approximately 107 jobs through contracts and direct hires.  In Monterey County, where the unemployment rate exceeded 17% this past winter, this was a huge boon to the economy.  Over $1.5 million of the $4.5 million grant was spent regionally on the purchase of equipment and supplies (such as steel sheet piling and rock riprap) further stretching the stimulus dollars.

Now that it is complete, this underwater retaining wall is working to slow the ebbing flow of the slough’s waters for the first time in more than sixty years—a feat that will reduce erosion and increase rare marsh habitat.  The engineering, permitting, and construction of this structure were all conducted under rigorous scrutiny and with input from the local community, and environmental monitoring ensured not only that that wildlife was unharmed, but that others interested in such a restoration project can learn from how it was done in the Elkhorn Slough.

General Information
This information will give you an overview of the proposed project without taking up a lot of your time.

PRESS RELEASE: Kirby Park Set as Staging Area for Elkhorn Slough Construction( 38KB, docx)

Project Objectives
The primary objective of the Parsons Slough Project is to reduce the tidal prism in Elkhorn Slough to minimize tidal marsh loss and habitat degradation as a result of tidal erosion and flooding, while maintaining sufficient tidal exchange and flushing to provide acceptable water quality. A secondary objective is to increase habitat diversity in Parsons Slough such that it better represents historic conditions.

Fact Sheet: Tidal Wetland Project and the Proposed Parsons Slough Restoration Project (pdf, 1.25MB)

Fact Sheet: Why Restore Elkhorn Slough? (pdf, 159KB)

Preliminary Project Description – a brief overview of the proposed project.

Supplemental Materials, November 2009 (.pdf 1.09MB) The material found here includes the goals, objectives, maps and other information associateed with the Preliminary Project Description.

Glossary of Terms – find definitions to commonly used words on our website and in our reports.

Summary Material

Parsons Slough is a 450-acre complex of mudflats and other tidal wetlands. This area historically supported 400 acres of tidal marsh, but now only 35 acres remain. In the first half of the twentieth century the area was diked off from the tides and drained for farming. The marsh soils dried and shrunk, lowering the land surface in a process called subsidence.


In late 1982, shortly after the land was acquired by the California Department of Fish and Game, the dikes around Parsons Slough broke. When the tides returned, currents, tidal scour and marsh loss accelerated throughout Elkhorn Slough.

Parsons Slough makes up 15 percent of Elkhorn Slough by land area, but because of subsidence it accounts for 35 percent of the daily exchange of tidal waters by volume. Powerful currents now prevent the establishment of salt marsh in Parsons Slough and contribute to tidal scour and the die back of salt marsh in the rest of the estuary.

Reducing tidal exchange at Parsons Slough would slow currents in many parts of Elkhorn Slough, increasing the viability of salt marsh and soft mud habitats throughout the estuary. Salt marsh can also be restored in Parsons Slough by adding sediment to raise the elevation of subsided former marshes.
The Parsons Slough planning process is evaluating how these strategies can be implemented to preserve Elkhorn Slough salt marshes and soft mud habitats while protecting the high quality existing habitat in Parsons Slough for sharks and rays, sea otters, seals and shorebirds.

We welcome your insights and contributions to the process.

Background on the Parsons Slough Wetland Restoration Plan

The State Coastal Conservancy (SCC), working closely with the Elkhorn Slough Reserve and Elkhorn Slough Foundation, has hired a consulting team led by Moffatt & Nichol to provide consulting services to develop a Parsons Slough Wetland Restoration Plan. The Plan will evaluate tidal marsh restoration alternatives for Parsons Slough including actions to reduce the tidal prism in the area and/or add sediment to rebuild marsh elevations. This Plan is part of the Elkhorn Slough Tidal Wetland Project.

aerial of slough

Additional details about the project scope can be found in the Request for Services (.pdf 597KB), in the Project Work Program (.doc 65KB), and in the Project Goals and Objectives (.doc 51KB).

Parsons Slough Project Update (.pdf 105KB, 6-3-0) This document summarizes the planning process for the restoration of Parsons Slough as of June, 2009, and describes management options that were considered feasible on a timeline of two to five years.

Technical Memoranda
Parsons Slough Sill – Base Options Report (.pdf 4.5MB) This technical memorandum presents twelve conceptual design for the sill base structure alternatives.

Parsons Slough Sill – Adjustable Weir Options Report (.pdf 2.4MB) This technical memorandum presents the three alternatives that were selected to move forward for evaluation in Task 2.3.

Parsons Restoration Team (PRT) Current Participants:

Trish Chapman1
California Coastal Conservancy
Jim Oakden
Moss Landing Marine Laboratories
Becky Suarez
Elkhorn Slough National Estuarine Research Reserve
Bryan Largay
Elkhorn Slough National Estuarine Research Reserve
Ross Clark
California Coastal Commission,
Central Coast
Mary Root
U.S. Fish and Wildlife Service,
John Krause
California Department of Fish and Game
Peter von Langen
Regional Water Quality Control Board, Central Coast
Cheryl McGovern
U.S. Environmental Protection Agency, Region 9
Lisa Windham
U.S. Geological Survey
Bill McIver
U.S. Fish and Wildlife Service,
Andrea Woolfolk
Elkhorn Slough National Estuarine Research Reserve
Katie Morange
California Coastal Commission

1 – Project Managers

Parsons Slough Restoration Planning Consultant Team Leads:

Moffatt & Nichol Chris Webb1, Dilip Trivedi1
Chambers Group, Inc. Noel Davis
Wetlands & Water Resources Stuart Siegel
FarWest Restoration Engineering Roger Leventhal
1 – Project Leads

Detailed Reports (and their Executive Summaries)
These four reports are full of information, and because of that they are also very large.  Choose the one that interests you the most, or read them all!

The Final Initial Study/ Mitigated Negative Declaration for the Parsons Slough Sill Project is now available.
Final Initial Study/ Mitigated negative Declaration – High Resolution, pdf, 18.6MB
Final Initial Study/ Mitigated negative Declaration – Compressed version, pdf, 6.9MB

Targeted Supplement Environmental Assessment (TSEA) – The National Environmental Policy Act (NEPA) requires federal agencies to integrate environmental values into their decision making processes by considering the environmental impacts of their proposed actions and reasonable alternatives to those actions. To meet NEPA requirements federal agencies prepare a detailed statement known as an Environmental Impact Statement (EIS). For the Parsons Project there was a Programmatic Environmental Assessment done at the program level. Download the Targeted Supplement Environmental Assessment (TSEA) for this project (6.11MB, pdf).

Final Initial Study/ Mitigated negative Declaration for the Parsons Slough Sill Project – an in-depth assessment of the potential positive and negative effects the proposed project could have on the Elkhorn Slough. It is written with the public in mind rather than for a scientific audience, and is one of the best ways to learn about the proposed project.
Final Initial Study/ Mitigated negative Declaration – High Resolution, pdf, 18.6MB
Final Initial Study/ Mitigated negative Declaration – Compressed version, pdf, 6.9MB
Draft still available – High Resolution, pdf, 17.5MB
Draft still available – Low Resolution, pdf, 6.5MB

Elkhorn Slough Tidal Wetland Project Hydrodynamic Modeling and Morphologic Projections of Large-Scale Restoration Actions FINAL REPORT (2008) – The final Philip Williams and Associates report on the projected effects of major actions on Elkhorn Slough hydrodynamics, geomorphology and habitats is available for download.  It describes the four different restoration alternatives that were considered for fixing the problems in Elkhorn Slough. Final Report including figures and conceptual design drawings (pdf, 43MB)

Elkhorn Slough Tidal Wetland Strategic Plan (2007) – This document summarizes the results of many technical discussions, scientific evaluations, and resource management decisions made over the past few years by participants in the Elkhorn Slough Tidal Wetland Project.  It is a guide for a variety of restoration projects for many years to come. Elkhorn Slough Tidal Wetland Strategic Plan – high resolution (ESTWP_PLAN_050207_hres.pdf, 20.4 MB)

Parsons Slough Wetland Restoration Plan Final (2010) – This detailed report examines the opportunities for ecological restoration of approximately 450 acres of intertidal habitats, including Parsons Slough, South Marsh, the Rookery Lagoon and other areas of the Elkhorn Slough National Estuarine Research Reserve.

Computer Model of the proposed project (2009) by Moffatt and Nichol – Check out this memo for a quick overview of the numerical modeling performed to simulate the proposed project’s possible impacts on the slough.

View a detailed map (available to download as a PDF in either  414KB or 246KB) with this Excel map legend (106KB .xls) to get descriptions of the many water control structures in Elkhorn Slough.