Projects

A decision support toolkit for the functional design of structure in living shorelines

End Date: 1/31/15

Abstract

The proposed research addresses the Healthy Coastal Ecosystems focus area identified in the research program announcement.  The objectives of the project are:  to perform a synthesis of knowledge pertaining to living shorelines; to document existing living shoreline technologies and project performance data; to measure the wave attenuating capabilities of living shoreline technologies; to determine the wave tolerance of coastal vegetation in the lee of breakwaters; and to develop a decision support toolkit that will improve the function and efficiency of living shorelines through a refined treatment of the role of structures in attenuating wave energy when wetland protection and habitat creation are express goals.  The toolkit will provide end-users with the tools and guidance necessary to prepare a functional design of a living shoreline structure that could be used in the preparation, funding, planning, or permitting phases of a project.  Moreover, the toolkit will allow end-users to identify and describe impacts of the structures on the study area; the viability of coastal wetland habitat in the lee of structures; expected ecological benefits of the structures; and the socioeconomic impacts of the living shoreline project.  Anticipated benefits to society include functional, more resilient, and more impactful living shorelines, with an ultimate goal of providing the framework for an alternative to bulkheads, seawalls, and revetments which eliminate or impair intertidal habitat.  The decision support toolkit will build upon past and current research by the authors on various aspects of living shorelines including wave transmission, ecological and biological impacts, and enhancement of ecosystem services.  The toolkit will benefit ongoing and proposed habitat enhancement projects in coastal Alabama, and will have regional and national impacts when distributed through collaboration with project partners and sponsors.  Targeted end-users of the decision support toolkit include resource managers, biologists, ecologists, engineers, academicians, and the general public.

Objectives

The goal of the project is to develop a decision support toolkit to assist resource managers and researchers in the proper design and placement of structures for living shorelines. In addition to its use as a design and planning tool, the proposed toolkit can be used to demonstrate to the community potential outcomes of living shoreline projects that incorporate different treatments and technologies. The objectives of the proposed two-year project are:

  • to coalesce existing documentation on the functional design of breakwaters for shoreline stabilization and coastal wetland habitat creation
  • to document and describe existing living shoreline technologies and describe their performance where possible
  • to perform detailed experiments on wave attenuating structures in the University of South Alabama Coastal Transportation Engineering Research and Education Center’s (CTEREC) wave basin
  • to develop a suite of technical and conceptual tools, and corresponding reference material, that can be applied to the selection, placement, and functional design of structures for living shorelines

Methodology

The proposed project will require a detailed synthesis of knowledge across many areas, documentation of existing living shoreline project performance data, detailed wave basin testing of living shoreline technologies, an investigation of the wave tolerance of coastal marsh vegetation in the lee of structures, and BETA testing of the toolkit using performance data from a well-documented living shoreline demonstration project in Alabama.

A comprehensive literature review will identify and summarize existing literature on the functional design of structures for shoreline stabilization, the engineering of wetlands in energetic wave conditions, documentation of the ecosystem services that living shorelines provide, and the results of several historical socioeconomic surveys to help better understand coastal resident perceptions and opinions on issues related to living shoreline projects. The literature review will provide useful and necessary details about the integral components and functions of living shorelines, and once synthesized into the decision support toolkit, will allow the end-user to better design their project to achieve a specific goal. Knowledge synthesized from the existing body of literature will allow the end-user to obtain performance projections related to wave energy reduction, modifications to the sand transport climate, shoreline response, spatial extent of wetland habitat coverage, ecological and biological enhancements (e.g. recruitment of oyster larvae), and impacts to the local ecosystem services. These performance projections will be supported through documentation and integration of existing living shoreline project performance data. Local, regional, and national living shoreline project performance data will be identified and inventoried.

A suite of experiments will be conducted in the USA CTEREC wave basin to document the wave transformation for a variety of living shoreline technologies. Examples include coir/bio logs, bagged oyster shell, Reef BallsTM, and ReefBLKSM. If funded, the authors will work with specified end-users to identify and test other technologies that may be used in future projects. The results of the wave basin testing will constitute a major component of the decision support toolkit, as they will allow an end-user to determine the size and proper location of a structure based on the incident wave climate. Some simple tools for describing and defining local wave climates will also be provided for the end-user as a supplement to the toolkit.

The wave tolerance of typical coastal wetland vegetation will not be tested in the CTEREC wave basin. The vegetation’s natural growing conditions cannot be replicated in the laboratory in a manner that would yield realistic and beneficial results. The wave tolerance of Spartina alterniflora has already been investigated by Co-PI #1, but recent research by a graduate student of Co-PI #1 suggests that this research should be revisited. The wave tolerance of vegetation in the lee of breakwater structures will be investigated through aerial imagery, project data, and local wave climate statistics to determine the limit of coastal wetland vegetation as a function of wave transmission and diffraction around structures. The approach proposed here will determine the effects of plant species, growing conditions, and other factors on wave tolerance.

Development of the decision support toolkit and corresponding resource documents will be based upon the results of the literature review, wave basin testing, vegetation tolerance research, and living shorelines project performance data. The toolkit will allow optimization of living shoreline structures across three priority areas: (1) shoreline stabilization, (2) coastal wetland habitat creation, and (3) ecological and biological enhancements. As such, the toolkit will require a combination of user input and user decisions that define the parameters of their project or project alternative. It is anticipated that the toolkit will be developed as a spreadsheet-based solution to avoid specific software requirements, but collaboration with end-users may result in technology transfer to a GIS-based platform (e.g. The Nature Conservancy’s Gulf Restoration Decision Support Tool). The performance of the decision support toolkit will be demonstrated through BETA testing using project performance data from well-documented living shorelines demonstration projects in Alabama. Potential projects include those at Point aux Pins and Alabama Port.

Rationale

The nation’s wetlands, which have naturally protected the shoreline for centuries are disappearing. Preventing this loss of wetlands along the coastlines has become a top priority. As wetlands have diminished, hardened structures such as bulkheads and seawalls have taken their place, resulting in a corresponding loss of intertidal habitat, and in some cases diminished water quality. In an effort to eliminate these structures, alternatives such as living shorelines are gaining popularity.
 
A key component of many living shoreline projects is a wave attenuating structure, or breakwater. The breakwater is typically placed offshore leaving an aquestrial zone between it and the shoreline. Well-designed structures can provide shoreline stabilization by modifying the local wave and sand transport climates. While energy dissipation is the primary goal of a breakwater, research has shown that they provide additional ecological habitat for aqueous as well as terrestrial biology, and generally tend to enhance a multitude of ecosystem services when integrated properly into the design of living shorelines. And while there are numerous references to the design and performance of breakwaters in the published literature, the functional design of breakwaters for living shorelines projects has not received detailed treatment.

Existing resources do not specifically address the implementation of structures in living shorelines where specific requirements on wave attenuation for vegetation, and habitat viability may exist. Nor do existing resources describe, in any amount of detail, the wave tolerance of various species of coastal marsh grasses under combined wave transformation processes in the lee of breakwater structures. Furthermore, the wave attenuating capabilities of living shoreline technologies (e.g. coir/bio logs, bagged oyster shell, Reef BallsTM, ReefBLKSM) have not been determined through detailed experimentation in such a manner as to be used to design fundamental breakwater characteristics, such as size and location, in order to achieve a measureable outcome (i.e. reduce wave energy by 50%, or facilitate the growth and expansion of Spartina alterniflora, etc.).

The proposed two-year project addresses the Healthy Coastal Ecosystems focus area identified in the 2012-2013 MASGC Bi-State Research Program announcement. Technical and conceptual tools developed as a result of the proposed research will improve the function and efficiency of living shorelines through a refined treatment of the role of structures in attenuating wave energy when wetland protection and habitat creation are express goals. The decision support toolkit will provide end-users, some of which have demonstrated their support of the proposed research by way of a letter of support, with the tools and guidance necessary to prepare a functional design of a living shoreline structure that could be used in the preparation, funding, planning, or permitting phases of a project. Moreover, the toolkit will allow end-users to identify and describe impacts of the structures on the study area, including adjacent shorelines; the viability of coastal wetland habitat in the lee of structures; expected ecological benefits of the structures; and the socioeconomic impacts of the living shoreline project. Anticipated benefits to society include functional, more resilient, and more impactful living shorelines, with an ultimate goal of providing the conceptual framework for an alternative to bulkheads, seawalls, and revetments which eliminate or significantly impair intertidal habitat.

The decision support toolkit will take advantage of past and current research by the PI and Co-PI’s on various aspects of living shorelines including wave transmission, ecological and biological impacts, and enhancement of ecosystem services. The toolkit will benefit from project performance data collected through four ongoing or recently completed projects in coastal Alabama as detailed in the proposal narrative (e.g. ). The toolkit will benefit a number of ongoing and proposed shoreline and estuary enhancement projects in coastal Alabama, including The Nature Conservancy’s 100:100 Restore Coastal Alabama project, and the Mobile Bay National Estuary Program’s Community-Based Restoration of Mon Louis Island. When distributed, the toolkit will have regional and national impacts on the function of living shorelines throughout the Gulf Coast region and along the eastern seaboard.

Targeted end-users of the decision support toolkit include resource managers, biologists, ecologists, engineers, academicians, and the general public. Specific letters of support have been obtained from the Alabama Department of Conservation and Natural Resources, State Lands Division-Coastal Section; the Mobile Bay National Estuary Program, and The Nature Conservancy. Dr. Chris Boyd, Mississippi State University, is an expert in living shorelines and has graciously agreed to serve as a project partner.

Results

Thesis: Observations of wave setup and transmission behind low-crested artificial reef breakwaters

Project final report