Environmentally sensitive boardwalks
Expanding trails while protecting sensitive areas
Building boardwalks across wetlands and streams has long posed an environmental challenge: how to anchor structures securely without damaging the sensitive ecosystems they aim to protect.
The Bainbridge Island Parks & Trails Foundation and Bainbridge Metro Parks have addressed this with a helical-pier system that significantly reduced construction impact while improving efficiency.
The system uses a hydraulic drill head mounted on a standard excavator to drive steel "screwpiles" deep into the ground. Each pile is capped with a brace that supports the boardwalk's crossbeams. This method disturbs very little soil and confines all construction activity to the trail's footprint, preserving surrounding vegetation and minimizing compaction.
Known informally as the "anchor auger" system, it was first used on the Old Mill to Blakely trail, where a small footbridge was needed to span a seasonal stream. Park District crews installed four 4-foot piles to support a 16-foot span, completing the project quickly with basic tools. The system has since been used on the Sound to Olympics Trail Sakai Connector, further demonstrating its versatility and low-impact benefits.
The most ambitious application to date has been at Hawley Cove Park, where a 130-foot boardwalk and viewing platforms were built to improve access for walkers and those with mobility challenges. The boardwalk connects to Hawley Cove's ADA parking area, enhancing connectivity between neighborhoods and the ferry terminal.
Building boardwalks with this system impacts only a small area – about 3 inches in diameter per pier – and the soil naturally backfilled as the auger drilled, leaving a clean, secure anchor with no visible trace once installed. The reduced environmental footprint minimizes the need for mitigation.
The Bainbridge Island Parks & Trails Foundation supported the equipment purchase with a grant to the Park District, showing our commitment to expanding trails through boardwalk construction while protecting sensitive areas.
