Quantifying Coastal Defense Value of Coastal Ecosystems

Speech Title:

Quantifying Coastal Defense Value of Coastal Ecosystems

Abstract  

Coastal ecosystems, such as seagrass and salt marsh, diminish the impact of storms on coastal communities. Predicting the value of these ecosystems with regard to coastal protection requires models for the interaction of fluid motion with flexible vegetation. This talk describes scaling laws to predict the drag on individual plants, and the extension of these laws to predicted wave decay over a marsh or seagrass meadow. This prediction enables a quantitative analysis of the economic benefit of these ecosystems, which is illustrated by the following case study. A seawall fronted by a marsh can be a hybrid, nature-based solution for both rural and urban coastal protection. The wave attenuation achieved by the vegetation can be translated into a reduction in seawall height required for the same level of coastal protection. Wave attenuation and benefit-cost ratio (BCR) are more sensitive to water depth than wave height, and for most marsh conditions the BCR indicates that marsh restoration is economically justified as an alternate to seawall heightening. The wave attenuation, and associated coastal protection value, can vary by a factor of three across different vegetation species.

Biographies

Dr. Nepf is the Donald and Martha Harleman Professor of Civil and Environmental Engineering at the Massachusetts Institute of Technology. She received her doctorate from Stanford University (1992) and was a Postdoctoral Fellow at Woods Hole Oceanographic Institution before beginning her career at MIT in 1993. She is internationally known for her work on the impact of vegetation on currents, waves, and sediment transport. She has been recognized by several awards, including: Schoemaker Best Paper Award [2012, IAHR], ASCE Hunter Rouse Award [2019], and IAHR M. Selim Yalin Lifetime Achievement Award [2023]. In 2018 she was elected as a Fellow of the American Geophysical Union.

Ernie In Him Lee is a PhD student in Civil and Environmental Engineering at the Massachusetts Institute of Technology. In his SM research, he applied physical wave modeling in a benefit cost analysis to explore the cost effectiveness of marsh-fronted seawall. He is currently using machine learning and computer vision to map marsh vegetation traits using drones.