How Much Marsh Restoration is Enough to Deliver Coastal Protection Benefits

Abstract:

As coastal communities grow more vulnerable to sea-level rise and increased storminess, communities have increasingly turned to nature-based solutions to bolster coastal resilience and protection. Marshes have significant wave attenuation properties and, as such, play an important role in coastal protection for many communities. Many restoration projects seek to maximize this ecosystem service but how much marsh restoration is enough to deliver benefits is still unknown. This question is critical to guiding efforts for funding, effort and overall cost effectiveness of projects. This study uses a series of SWAN model simulations to determine empirical relationships between wave attenuation and marsh unvegetated-vegetated ratio (UVVR), a geospatially-derived metric of vegetation cover. The model runs consider several different common marsh morphologies (including systems with channels, ponds, and fringing mudflats), vegetation placement, and simulated storm intensity. Wave energy attenuation benefits are seen at as low as ~30% vegetation cover (UVVR value of 2.3), providing important insight for coastal practitioners and managers seeking timely performance goals and metrics for marsh restoration, enhancement, and creation.