R/HAZ-1a

Impact/Outcome:

This section describes how this project has advanced scientific knowledge and/or made a difference for coastal residents, communities, and environments. Maryland Sea Grant has reported these details to the National Oceanic and Atmospheric Administration (NOAA), one of our funding sponsors.

Summary: A study found that different types of shoreline stabilization techniques in Chesapeake Bay, such as hardened and natural shorelines, are associated with different patterns of local sedimentation. This project contributed evidence and understanding of an aspect of ecosystem dynamics that is highly complex and variable. Improved information may eventually help planners minimize harmful effects of human-driven shoreline modifications on water quality and aquatic vegetation.

Relevance: Sixty-nine percent of Maryland’s shorelines are eroding. Erosion rates and coastal flooding are likely to increase due to sea level rise caused by climate change. A variety of shoreline stabilization techniques are used in Maryland’s portion of Chesapeake Bay. But there are few quantitative, long-term data available about how well these techniques control erosion and promote near-shore water quality and abundance of submerged aquatic vegetation (SAV) — information that is useful to resource managers and land use planners. 

Response: Building on previous studies, researchers from the University of Maryland Center for Environmental Science collected data from 17 sites in Maryland representing a variety of shoreline stabilization mechanisms. These included riprap, landscaped vegetated shorelines (a.k.a. “living shorelines”), and offshore breakwaters as well as baseline sites with no stabilization. At each site, the researchers measured sedimentation rates and sediment types before and after stabilization techniques were applied and characterized whether the changes observed were likely to increase or diminish SAV growth. In addition, a graduate fellow supported by Maryland Sea Grant, Jia Gao, conducted related research to create an updated wind climate model for the Maryland portion of the Chesapeake Bay, which the research team used to study stabilized shoreline sites.

Results: The researchers made a novel set of findings about associations between different kinds of shoreline hardening and sedimentation patterns. Riprapped and living shorelines appeared to decrease the transport of fine sediments (clays, silts) and organic material from land into the adjacent nearshore waters. Riprap projects also may increase the supply of coarser (sand) sediments to the nearshore when sand is used to fill in gaps in these built barriers. These conditions are beneficial for SAV growth because SAV prefers coarser (sand) sediments to finer (mud) ones as a growth substrate. The study also found that offshore breakwaters promoted accumulation of finer sediments on their landward side, which could prove detrimental to SAV. The researchers documented a range of sedimentation responses associated with variations in local conditions. By identifying a range of variability and uncertainty in these responses, this project has identified important questions for further study. The scientists presented these findings at national scientific meetings and a regional summit on living shorelines and to the Chesapeake Bay Program Office (CBPO) Modeling Workgroup. In addition, Cindy Palinkas, one of the co-principal investigators, is participating in a CBPO project to produce a revised technical synthesis report about SAV restoration in Chesapeake Bay. This project’s findings will inform a section of the report about effects of land use, including shoreline hardening, on SAV. Jia Gao’s modeling work is relevant to refining existing models to predict the effects of sea level rise and wind conditions on erosion rates along the estuary’s shorelines.