Where Once there was a Runway

Returning the Former Hamilton Army Airfield to Nature

While a partnership between the San Francisco District of the U.S. Army Corps of Engineers and the California State Coastal Conservancy in April 2014 beneficially completed an 11-year project to return 648-acres of the former Hamilton Army Airfield into wetlands habitat, in many ways, the restoration effort is just getting started.

 

By Edward Keller, P.E.

 


 

Less than 25-mi north of the Golden Gate Bridge, the Hamilton Wetlands Restoration Project is transforming parts of the former Hamilton Army Airfield into an array of wetland and wildlife habitats while beneficially reusing dredged mate­rial from harbor deepening in Oakland. The restoration has returned 380-acres to tidal wetlands and created 150 acres of seasonal wetlands—open space for migra­tory birds and endangered species such as California clapper rails and salt marsh harvest mice that depend on salt marshes. The project also includes over 100-acres of upland habitats that provide connectivity for wildlife that traverse the site and a new 2.7-mi stretch of the Bay Trail for walking and wildlife viewing.

Hamilton Wetlands Restoration Project

About 85 percent to 90 percent of the original tidal marshes in the San Francisco Bay-Delta have disappeared—either filled or substantially altered for agriculture, urban development and salt produc­tion. The loss caused a decline in marsh-dependent wildlife in the Bay, with some species threatened with extinction. In addition, bayside areas lost the marshes natural ability to protect against floods and filter pollution and excess nutrient runoff. Restoration will recreate habitat for many birds, fish and animals and improve the physical, chemical and biological health of the Bay. It also will create opportunities for wildlife-oriented recreation for generations of area residents and visitors. 




HISTORIC LEGACY

The former Hamilton Army Airfield is located in Novato, Calif., on the margin of San Francisco Bay. The land had been used for agriculture since it was reclaimed in the 1800s. Once the dikes were constructed and the land dried out, it began to subside. Hamilton was constructed by the Army Air Corps on these reclaimed, subsided lands in the early 1930s and was commissioned in 1935. With its sweeping views of the Bay and its Mediterranean architecture, the base soon became a premier military post. It was renamed Hamilton Air Force Base in 1947 when the U.S. Air Force took over. Over the years the installation hosted various fighter and bomber groups and played a major role in deploying and receiving thousands of troops and refugees from the Pacific Theater.

Hamilton Army Airfield, circa 1970s

In the mid-1970s, the Air Force curtailed operations at the base, leaving Hamilton for facilities that could support larger, heavier aircraft, which required longer runways. The Army once again began using portions of the installation, primarily for Army Reserve operations and training, and its name reverted back to Hamilton Army Airfield. These operations were short lived, however. The base was selected for closure in 1988, a decision that encompassed the airfield, hospital building and most major facilities. The Base Realignment and Closure Act of 1995 officially shut down the remain­ing operations, as the U.S. Navy had been utilizing on-base housing at Hamilton, but that was no longer needed when the service closed its remaining installations in the area. A third portion of the property also earlier had become the responsibility of the U.S. General Services Administration while the U.S. Coast Guard still maintains adjacent property as the home of its Pacific Strike Team. The history of Hamilton Airfield, even before the restoration work began, was nothing short of complex.

 

BENEFICIAL SOLUTION

The reuse plan for the installation included commercial space, residen­tial neighborhoods and open space and wetlands. Environmental cleanup was undertaken to prepare the property for its next life. In 2003, 630-acres of the former airfield were transferred to the California State Coastal Conservancy. The Conservancy was also granted 18-acres from the Navy for this restoration project. Although planning and design efforts had been underway for a number of years, this signified the beginning of the Hamilton restoration work on the ground.

The Hamilton Wetlands Restoration Project is a joint project of the San Francisco District of the U.S. Army Corps of Engineers (USACE) and the California State Coastal Conservancy. The agencies work closely with area partners including the City of Novato, the Novato Sanitary District, Marin County and the San Francisco Bay Conservation and Development Commission. Numerous community work­shops have been conducted to solicit public comment on the project as well.

One of the key successes of the project has been the utilization of dredged material to help restore subsidence. Dredged material serves as the foundation for establishing the kind of topography conducive for growing plants and attracting wildlife. The Hamilton parcel, over time, had subsided up to 10-ft or more. A large quantity of fill would be required in order to create wetland habi­tat. While San Francisco Bay has limited capacity for the aquatic placement of dredge material, it is home to a number of deep draft channels that require dredging to maintain safe navigation. One of these is the Port of Oakland, which at the time was embarking on a 50-ft harbor deepening project. There would be a plethora of dredge material to find a home for.

 

MISSION AUTHORIZATION

The Hamilton Wetlands Restoration Project was authorized as part of USACE’s Civil Works environmental restoration mission. This authorization allowed the project to prepare the site and to fund the incremental increase in cost associated with the delivery and placement of dredge material. The authorization for the Oakland Harbor Deepening Project specifically named Hamilton as one location where deepening material would be beneficially used for habitat restoration.

These synergies and authorizations tied together USACE’s ecosystem restoration and navigation missions. Work from 2003–2007 primarily included building demolition and site preparation, includ­ing perimeter levees and infrastructure to import dredge material.

 


 The Hamilton Wetlands Restoration Project is unique in that it creates both tidal and seasonal wetlands along with tidal panes and upland habitat. This site design works with nature to provide a variety of habitat types, laying out a template for nature to complete.


 

From 2007 to 2011, 5.8-million-yd³ of sediment was diverted from ocean or in-bay disposal and pumped onto the Hamilton site to raise the elevations. Since San Francisco Bay is naturally shallow, an offloading system was constructed near the deep draft channel, 5-mi offshore. Dredge material was delivered to the offloader in scows up to 5,000-yd³ in size. Bay water was used to slurry the dredge material to enable it to be pumped to the site through a 24-in diameter pipeline. An offshore booster and landside booster were necessary to keep the material moving. The entire offloading system, to meet air quality criteria, used electrical power, which was supplied by a project installed temporary substation.

Prior to the placement of dredge material, perimeter levees and internal berms along with weir structures had been constructed to create placement cells. The cells were filled in an orderly manner, using sandy material to build a base in areas where greater depths of cover were required. It was necessary to continually manage the place­ment of sandy material to prevent it from piling up at the discharge point. In most areas the sandy material then was covered with fine grained material to support the wetland biota. Fine grained material remained in suspension for a longer period of time and required more on site management to clarify the process water. The clarified process water was discharged to the Bay at a rate of 8-million-gal per day.

At one time, the offloading and placement operation continued 24/7 for a two-year period without a shutdown of more than two weeks. The dredge material delivered to the site came from Oakland Harbor as well as a number of smaller maintenance dredging projects.

Dredge operations at the Port of OaklandThe seasonal habitat includes ponds that were sculpted from the dredge material after placement. These areas of the site had to be dried out in order to be able to work the fine grained material and compact pond bottoms to hold water. At the same time, the tidal wetland portions of the site had to be maintained in a wet condition so that the material would not dry and desiccate. This section was maintained in a much softer condition so that nature would be able to form channels in a more natural manner.

 

IMPACT OVER TIME

The Hamilton Wetlands Restoration Project is unique in that it creates both tidal and seasonal wetlands along with tidal panes and upland habitat. This site design works with nature to provide a variety of habitat types, laying out a template for nature to complete. The overall site template increases in elevation with distance from the Bay. As sea level rise occurs, the overall percentages of tidal versus seasonal habi­tat will naturally adjust, but both will still exist. The main channel cut to reconnect the site to the bay was sized to ensure a full tidal exchange will take place to ensure site development.

In April 2014, 648-acres of restored wetlands were opened to tidal action from San Francisco Bay. And while this phase of the project is complete, complet­ing an 11-year journey involving multiple stakeholders, environmental engineering, design, dredging, planning and permitting efforts, the work at the former Hamilton Army Airfield is hardly done.

A plant nursery was constructed to produce the native plant material needed for the seasonal and upland portions of the site. This effort is to ensure that native plants get a foothold to combat invasive plant species. Over a three-year period the nursery will be propagating more than 30,000 plants to be transplanted to the site. This propagation and planting effort has engaged a cadre of local volunteers and school groups.

It is anticipated the site will develop in the years to come and USACE will continue to monitor it over the next 13 years. The data gained from monitoring the development of this project should inform the designs of future wetland creation projects.

 


 

Edward Keller, P.E., is Chief, Environmental Section A, USACE San Francisco District; 415-503-6841, or This email address is being protected from spambots. You need JavaScript enabled to view it." target="_blank">This email address is being protected from spambots. You need JavaScript enabled to view it..