NUMERICAL MODELS, A TOOL FOR BALANCING REGULATORY AND STAKE HOLDER CONCERNS IN THE RESTORATION OF DEGRADED WETLAND SYSTEMS

摘要

The restoration of coastal wetlands and salt marshes is one of the keys to improving the biodiversity within the coastal ecosystem. Many wetland ecosystems have been severely impacted due to anthropogenic effects. One of the challenges in restoring a degraded salt marsh is to assess the impacted value of the degraded wetland system that has evolved and then to project what changes the proposed restoration will have on the existing ecosystem. The restoration of these impacted systems often results in habitat swapping. Most commonly in New England a brackish or fresh water wetland system will have developed along the transitional areas of the wetland. These impacted or degraded systems are unstable in that they owe their existence to the artificially altered wetland hydraulics. Because restoring a tidal wetland usually involves changes to the tidal hydraulics and vegetation, questions are often raised by the stakeholders as to what impact the restoration will have on them. Addressing the concerns of stakeholders and regulatory agencies is often a balancing act that requires the project proponent to develop an accurate projection of the changes that will occur as a result of the restoration project. The wetland restoration project discussed is located at South Cape Beach in Mashpee, MA and is connected to the Waquoit Bay estuary. The South Cape Beach wetland system is composed of salt marsh and brackish marsh that includes fresh emergent, shrub scrub and forested wetlands. The 2-dimensional numerical model RMA2 was used to evaluate design alternatives and to assess their impact on design parameters such as tidal range and velocities, upland flooding, and potential marsh plain erosion. Due to the extended degradation of the system that has occurred, the substrate within the system, the potential for upland flooding, and the vegetation impacts, including the affect on the forested upland habitat were critical components in evaluation of each design alternative considered. Evaluation of the design alternatives required a unique balancing of competing interests that included restoring salt marsh, minimizing potential forested upland die off, controlling Phragmites australis, assessing potential flooding impacts and projecting changes that would occur as a result of implementing the selected design alternative.