Examining Wave Attenuation Rates and Subsurface Pore Pressures Across Three Marsh Restoration Sill Structures on a Sandy Bed.

Jordan Converse, Oregon State University, Corvallis, OR, United States, Tyler Will Miesse, George Mason University, Fairfax, VA, United States and Meagan E. Wengrove, Oregon State University, Department of Civil and Construction Engineering, Corvallis, United States
Abstract:
With rising sea levels and more frequent exposure to extreme storm conditions, coastlines worldwide are vulnerable to increased erosion and loss of natural marsh lands. In an effort to lessen these impacts, there is a growing practice of adapting hard or “grey” coastline protection techniques to more nature-based features that promote habitat and ecosystem health. Marsh restoration, herein referred to as ‘living shorelines’, utilizes natural and nature-based materials to protect marsh shores from erosion while also allowing intertidal flushing to promote the health and diversity of the marsh. Our study investigates three types of living shoreline sill designs for medium to high energy marsh restoration sites, specifically; tree root wads, rock, and rock-reinforced oyster shell, against varying wave conditions at three different storm surge water levels. Large scale laboratory experiments were conducted in the large wave flume at the O.H. Hindsdale Wave Research Laboratory. Design wave and water level conditions were estimated using NOAA Buoy Data and calculated fetch distances spanning eleven different marshlands on the east, west, and gulf coasts of the U.S. Wave attenuation rates over the sills were quantified through measured wave transmission coefficients using single-point velocimeters positioned in front of and behind the sill. Scour of the sill was measured using sonar altimeters and pore-water pressure sensors were vertically stacked in pairs and positioned along the longitudinal sill width of to study the effect of momentary liquefaction on sill stability. Results will contribute to understanding the effect of sill material porosity and mass on structure stability, and the effectiveness of using more green (oyster shells and root wads) compared to grey living shoreline sill structures in the continued effort to establish design criteria for living shoreline implementation.