Sawmill Creek Wildlife Management Area

Hydrodynamic and sediment transport modeling informs the design of nature-based protection solutions to restore tidal flow, ecological function, and resilience to 740 acres of tidal marsh.

Once a thriving tidal marsh, the 1,340-acre Sawmill Creek Basin has been highly impacted by anthropogenic disturbances over the last two centuries. Dikes, tide gates, and other modifications altered natural hydrology and severely degraded ecosystem services such as habitat, carbon sequestration, storm surge protection, and water quality improvement. Although tidal flow was restored to the eastern marsh in 1950, when the tide gates and dikes were breached during a Nor’easter, marsh subsidence and large swaths of mudflats and open water remained. The western portion of the basin, which includes a meadow created with construction fill in the 1960s and a bermed trail bisecting the basin, experienced wetland loss due to restricted tidal flow. In addition to its degraded habitat and ecological function, the basin had become a carbon source rather than a sink.

As a critical first step in advancing the New Jersey Sports and Exhibition Authority’s Meadowlands Research and Restoration Institute’s (NJSEA) vision of a restored mosaic of functioning coastal habitats, Biohabitats developed a two-dimensional hydrodynamic and sediment transport model for the channels, mudflat, and marsh in the 740-acre eastern portion of the site in order to understand the existing conditions within the tidal system. Informed by detailed LiDAR and hydrodynamic monitoring, the model was used to determine restoration approaches and identify potential pilot projects.

Biohabitats then expanded the model to include the 650-acre western portion of the basin and to evaluate the hydraulic impacts of a bermed trail and culverts that restrict tidal flow and create unsuitable conditions for target marsh vegetation. The project area also includes the Harrier Meadow Wetland Enhancement site, which is hydrologically connected to the mudflats of the western basin. After completing a survey of the culverts, Biohabitats collaborated with NJSEA to collect channel depth data throughout the mudflat area to supplement LIDAR. Biohabitats then synthesized the field data into the model to create an accurate surface layer. The model, which characterizes hydrodynamic conditions and will inform NJSEA of suitable restoration approaches, also considers the impact of sea level rise to more accurately determine the site’s full ecological and carbon sequestration value into the future. Additionally, this model will examine the salinity throughout the project area, particularly in the Harrier Meadows area. This will inform how the ecosystem has changed from historical conditions and provide insight for how to restore high marsh conditions. Transport of sediment throughout the system is also being modeled. Areas of sediment accretion/erosion as well as velocities and shear stresses will inform which areas may be suitable locations for proposed restoration alternatives.

Based on this ongoing work, Biohabitats also led the design and permitting of experimental marsh islands and other nature-based protection measures. These designs utilize the unique features of the area and a combination of different methods and materials to serve as pilot projects that demonstrate and help determine the effectiveness of alternative restoration strategies in similar mudflat settings across the region, with the hope that these pilot projects can be recreated at additional sites in the future. The Biohabitats team understood the critical hydrodynamic and sediment transport considerations that ultimately influenced the design and had the tools available to explore innovative restoration approaches to return ecosystem services, habitat diversity, and carbon sequestration to the mudflats.

TAGS

• Analysis+Planning
• Assessment+Monitoring
• Climate Adaptation + Resilience
• Ecological Restoration