Creating a Scenic Walkway in Marin County, California

By Erik Skindrud, regional editor

The pathway?EUR??,,????'???s surface is neatly formed of decomposed granite mixed with organic material and pressed into place. The project?EUR??,,????'???s extensive erosion-control system includes the fence visible at left. Benches (foreground and center background) were added to let visitors enjoy the view of the wetlands and bay.

This San Francisco Bay Area trail measures about a half mile in length. But the short distance didn?EUR??,,????'???t free the design team and construction crew from paying close attention to a host of erosion, cost and construction details.

Reservoir Hill overlooks the former Hamilton Army Airfield in Marin County, Calif., where the first atomic bombs were delivered in 1945 before being shipped to the Pacific. Later called Hamilton Air Force Base, the facility was closed in the mid-1970s and now sits in a residential section of Novato, about 15 miles north of San Francisco.

Reservoir Hill is now adjacent to homes. The broad, flat area between it and the San Francisco Bay will soon be returned to its natural state through one of the biggest restoration projects in the country. The changes that have come to the area made it a perfect candidate for additional recreation facilities, which is what the neighbors and the City of Novato decided to do back in 2003.

Reservoir Hill?EUR??,,????'???s proximity to a part of the San Francisco Bay Trail helped the project secure funds from a number of state and local sources. In April 2003, a planning meeting was held that helped determine the shape of a walking trail that would lead to an overlook at the hill?EUR??,,????'???s summit, offering dramatic views of the coastal hills to the west and of the mud flats, former airfield and bay to the east.

Just half a mile in length, the project offered several engineering challenges. ?EUR??,,????'??You?EUR??,,????'???re out in the middle of nowhere?EUR??,,????'??+away from the sewer system?EUR??,,????'??+so you have to deal with runoff on site,?EUR??,,????'?? project superintendent John Heing said. ?EUR??,,????'??There?EUR??,,????'???s no other way to get rid of it without creating an erosion problem.?EUR??,,????'??

Redwood covers mark the drainage points where water from the trailside gullies is diverted to the water dissipater fields. The straw wattles at left keep rainfall from flowing along the edge of the gully?EUR??,,????'???s riprap.

Heing, of Petaluma, Calif.-based North Bay Construction, described how crews built a total of eight ?EUR??,,????'??water dissipaters?EUR??,,????'???EUR??,,????'??+structures that help runoff from trail surfaces percolate safely into the ground. The system begins with riprap-lined drainage channels that run along the downslopes of the trails. The channels lead to drain structures that send the runoff to 20-foot sections of plastic pipe that are buried two-and-a-half feet under the ground. The pipe leads to the water-dissipater structures, which are rectangles of riprap set on 500X Marifi stabilization fabric.

The buried plastic pipe delivers runoff to the dissipater field where it can settle and percolate without creating erosion problems. Additionally, the underground pipe is perforated with thousands of holes to further spread the water around.

The $375,000 budget forced planners to make some tough decisions. One option would have made the walkway accessible for the entire length by Americans with Disabilities Act (ADA) guidelines. But that would have required a trail with many more turns snaking for a much longer distance up the hillside. The 100 percent option would have doubled the total length of the trail, which would have made it considerably more expensive. ?EUR??,,????'??The trouble with that option was the hill is too steep, you?EUR??,,????'???d have switchbacks all over the place,?EUR??,,????'?? project superintendent Heing explained.

The worker at left is mortaring the top segments of a retaining wall for the Reservoir Hill Trail?EUR??,,????'???s parking area off Hamilton Parkway in Novato, Calif. The trail will lead to the top of the oak-covered hill behind the workers. It looks like a large open space here, but the area is actually a narrow greenbelt that is sandwiched between housing developments.

As built, about 65 percent of the trail meets ADA standards, the project landscape architect said.

?EUR??,,????'??We tried to create a balance, where at least part of the trail is fully accessible,?EUR??,,????'?? Maisha Ruth of RHL Design Group, Inc. told LCN. ?EUR??,,????'??Even if you don?EUR??,,????'???t go all the way to the top, it provides a good view and a good experience for users with different abilities.?EUR??,,????'??

This rock field is one of eight ?EUR??,,????'??water dissipaters?EUR??,,????'?? where water captured by trailside gullies is diverted. The stones hide a layer of Marifi stabilization fabric. Together, rocks and fabric let water percolate into the soil without eroding adjacent areas.

Getting the Job Done

North Bay Construction completed the job on time and under budget. The project work started on July 26 and was completed before Christmas 2004, City of Novato engineer Michael Hanlon said.

About a third of the trail grade was already on site as the asphalt Reservoir Hill Road. The North Bay crew extended the route with a D4 Caterpillar dozer. A tractor with a front-end loader and a rear-mounted scraper helped bring in tons of decomposed granite to make up a permeable but mud-free surface for the new portion of the path.

The extended portion, which makes up more than half of the walkway?EUR??,,????'???s length, was built with a width of just five feet. That cut down on cost but makes vehicular access difficult, eliminating police patrols and maintenance visits.

Project planners wanted to keep tree plantings to a minimum but a landscaped buffer was called for to separate the trail from neighboring homes on Serra Court and the adjacent Bayside subdivision. The trees are cork oaks, with manzanita and coyote bush rounding out the mix.

Balancing the Options

RHL presented the preliminary trail design with cost estimates at a concept design meeting attended by staff from the Novato parks and recreation, public works and staff from the Novato Fire Protection District. Three trail concepts were presented, ranging from 100 percent ADA accessible trail to zero-percent accessible. Due to budget constraints, the 100 percent concept was eliminated due to the high cost. On April 24, 2003, a community meeting was held to share the accessible trail plan and to secure feedback and hear suggestions, concerns and resident issues. There was full support for the trail plan, however, the desire for more trail access points so that people can exit the trail without having to return all the way to the south end where they started, was high. Several points of trail access were identified as desired by the residents. They are listed as follows.

The air base?EUR??,,????'???s former runways occupied the flat area in the left rear of this photo. Taken in December, 2004, this photo shows areas of hillside that had been scraped clean nicely filled in with hydroseeded grass. An erosion-control fence is visible at right.

Alternate Access Points

At the meeting there were divergent views regarding access off of Serra Court among residents living on the street. The homeowner most impacted by Serra Court access, since his property touches the city-owned property that could be used for the access, described the impacts he experienced when Serra Court did provide access a few years ago.

Currently there is an unnamed road that comes off of Hamilton Parkway just east of the community skate park that provides access to the former air base?EUR??,,????'???s runways. Eventually, this access road to the runways will serve as the haul road for the wetlands construction. The road passes a treatment plant and just slightly northeast of the building is the future location of the Wetlands Interpretive Center when funding is secured.

A log fence was installed on the hilltop to protect cyclists and pedestrians from a water tub and other historical remnants. The decomposed granite pathway surrounding the fence offers dramatic views.

Other Concerns and Community Wishes

Some other comments and responses surfaced at the community meeting. Several attendees expressed concern for the preservation of wildlife on Reservoir Hill, particularly as affected by loose dogs.

A request was also made that the interpretive signage planned for the trail on Reservoir Hill include a history of the area, the use of the hill, and the events connected to the military. The local Bay Institute has indicated some interest in participating in the interpretive portion of the project. The planners will discuss signage on plants and wildlife with the institute. For military history, the Novato Historical Guild may research any information that is available.

A need for rest stops and seating along the trail was identified too. As the budget allowed, the team provided additional seating on the trail. As outlined in the 65 percent accessible plan, there are some retaining walls that can double as seating or provide nice rest stops.

Requests for trash cans and dog "mutt mitt" dispensers along the trail were also made at the planning meeting.

At the meeting there was a question about the hours that the trail would be open. It was also suggested that set hours aren?EUR??,,????'???t really necessary. Trail users may wish to do star gazing from the trail and vista overlook, and with a flashlight, might be able to navigate the trail. But current city park hours, per city code, are from 6 a.m. to 10 p.m., unless designated otherwise.

Engineer Michael Hanlon of the City of Novato checks out a section of decomposed granite trail and straw-wattle-guarded gully with park planner Pamela Shinault.

Final Landscaping and Final Touches

Planners decided to limit any planting to the Hamilton Parkway parking area and along the first third of the project?EUR??,,????'??+where it parallels Serra Court. The idea was to leave the hill in as close to a natural state as possible, while creating a native-plant buffer where the project borders residential areas.

Neary Landscape, Inc. of San Rafael was the project subcontractor that handled the latter task. Crews planted a total of 14 cork oaks, 18 common manzanita and 88 coyote bush shrubs?EUR??,,????'??+all native California flora. Additionally, the workers hydroseeded close to two acres to assist with erosion control.

In the end, budget constraints prevented the installation of restroom facilities at the Hamilton Parkway trailhead and limited the walkway?EUR??,,????'???s overall ADA accessibility. But as planned, the project was completed under budget?EUR??,,????'??+although one final step remains.

Given the critical nature of the hill?EUR??,,????'???s erosion issues, engineers have saved a small portion of the total budget to inspect the hillside in March and April. The city will then fine-tune the hill?EUR??,,????'???s erosion control to correct any shortcomings.

?EUR??,,????'??We?EUR??,,????'???re going to inspect how it performs this rainy season,?EUR??,,????'?? Novato engineer Michael Hanlon explained. ?EUR??,,????'??We managed the funds pretty well throughout the project?EUR??,,????'??+we still have some remaining. So we?EUR??,,????'???re going to go out this spring and manage the long-term health of the project.?EUR??,,????'??