Mercer Island Shoreline and Watercourse Buffer Mitigation with Stormwater-Optimized Hardscape

Residential | Environmental | hardscape + stormwater + compensatory mitigation

A steep Mercer Island waterfront property built around water management and long-term stability. Major hardscape work was paired with mitigation planting in both the shoreline buffer and a piped watercourse buffer, completed per approved plans and conditions using native plant stock in the regulated areas.

Work completed

• Hardscape
  • Retaining wall system: Belgard Tandem Modular Wall System
  • Patio surface: Techo-Bloc Para slabs
  • Stairs and landings for safe access
  • Terraced grade to create a usable patio and spa
  • Tree Protection Zones (TPZ) established and observed during hardscape installation
• Drainage built for clay soils
  • Retaining wall drains piped to a series of stormwater detention vaults
  • Ultra-deep, washed aggregate bases under patio and wall sections for stability and drainage function
  • Subgrade shaping and sequencing that prioritized drainage performance
• Mitigation planting
  • Shoreline buffer mitigation planting installed per approved plans and conditions
  • Watercourse buffer mitigation planting along a piped watercourse, installed per approved plans and conditions
  • Japanese Knotweed removal in shoreline buffer
  • Native plant stock used within buffer areas

Design + delivery

• Mitigation design: Facet
• Hardscape design: PGC staff designer Marco Downs
• Invasives removal: PGC staff consultant Dan Weber

Outcomes

• Stable terraces and safe access on a steep, clay site
• Drainage and stormwater functions integrated into the hardscape build
• Buffer mitigation planting integrated into the surrounding ornamental landscape