Mitigating Erosion Along Sheltered Coasts

Transcription

1 Mitigating Erosion Along Sheltered Coasts A report of the National Academies Susan Roberts and the Committee on Mitigating Erosion Along Sheltered Coasts 1

2 Sponsors Environmental Protection Agency U.S. Army Corps of Engineers Cooperative Institute for Coastal and Estuarine Environmental Technology NOAA Coastal Services Center 2

3 Statement of Task The study will examine the impacts of shoreline management on sheltered coastal environments (e.g. estuaries, bays, lagoons, mud flats, deltaic coasts) and identify conventional and alternative strategies to minimize potential negative impacts to adjacent or nearby coastal resources. The study will provide a framework for collaboration between different levels of government, conservancies, and property owners to aid in making decisions regarding the most appropriate alternatives for shoreline protection. 3

4 Committee JEFF BENOIT, Chair, SRA International, Arlington, Virginia C. SCOTT HARDAWAY, JR., College of William and Mary, Virginia Institute of Marine Science, Gloucester Point DEBRA HERNANDEZ, Hernandez and Company, Isle of Palms, South Carolina ROBERT HOLMAN, Oregon State University, College of Oceanic Atmospheric Sciences, Corvallis EVAMARIA KOCH, University of Maryland, Center for Environmental Science, Horn Point Laboratory, Cambridge NEIL MCLELLAN, Shiner Moseley and Associates, Houston, Texas SUSAN PETERSON, Teal Partners, Rochester, Massachusetts DENISE REED, University of New Orleans, Department of Geology and Geophysics, New Orleans, Louisiana DANIEL SUMAN, University of Miami, Rosenstiel School of Marine and Atmospheric Science, Miami, Florida Staff SUSAN ROBERTS, Study Director AMANDA BABSON, Christine Mirzayan Science and Technology Policy Fellow SARAH CAPOTE, Senior Program Assistant 4

5 The Problem Sheltered coasts are sites of increasing development, with many people moving to the coast; Sheltered coasts are vulnerable to chronic land loss from erosion and sea level rise; Landowners often select hardening technologies such as bulkheads, revetments, and groins to prevent land loss even when effective, softer alternatives are available. 5

6 Beach Loss after Installation of Bulkhead Source: After Tait and Griggs (1990) and Douglass (2005) 6

7 Beach of the Future? 7

8 Sea Level Rise 8

9 New NRC Report: Sea-Level Rise for the Coasts of CA, OR, and WA Natural shorelines provide partial protection for coastal development; The net result of storms and SLR is coastline retreat, ranging from cm (hard) to meters (soft) per year; Maintenance of marshes requires accumulation of organic material, adequate sediment supply, and space to move inland. 9

10 Shorelines at Risk Three major geomorphic settings: Beaches and dunes Mudflats and vegetated communities (marsh, mangrove, seagrass, etc.) Unconsolidated bluffs 10

11 Ecosystem Services - Beaches 11

12 Ecosystem Services - Marshes 12

13 Ecosystem Services - Bluffs 13

14 Findings and Recommendations Cumulative Effects Erosion Mitigation and Permitting Shoreline Management Planning Information Needs 14

15 FINDING: CUMULATIVE EFFECTS The cumulative impact of the loss of many small parcels can alter the properties, composition, and functioning of the ecosystem. Also, the economic, recreational, and esthetic properties of the shoreline will change with potential loss of public use, access, and scenic values. RECOMMENDATION: Shoreline management plans need to address potential cumulative effects of shoreline hardening. Hardening projects could then be limited to areas unsuited to non-structural alternatives or sites where structures are predicted to have less impact. 15

16 EROSION MITIGATION AND PERMITTING FINDINGS: Compared to open coasts, a greater variety of techniques are available to address erosion in sheltered areas New techniques (or structural materials) require a rigorous process of testing and evaluation to determine their effectiveness and evaluate their environmental impacts The current permitting system discourages the use of alternatives to shoreline hardening 16

17 EROSION MITIGATION AND PERMITTING RECOMMENDATION: State and federal regulatory programs should establish a technical assistance function to provide advice on permitting issues and information on types of erosion mitigation approaches and their effectiveness under various site conditions. 17

18 SHORELINE MANAGEMENT PLANNING FINDINGS: Many factors in addition to sediment budgets must be considered in the development of regional shoreline management plans including socioeconomic factors (e.g., ownership of the shoreline, waterfront property values, beach access for recreational boating and fishing) and a broad range of ecological issues. 18

19 SHORELINE MANAGEMENT PLANNING FINDINGS (continued): Regional shoreline management plans could be implemented under the auspices of the federal Coastal Zone Management Act (CZMA), Section Special Area Management Plans, to ensure that federal permitting actions are consistent with the plan. 19

20 SHORELINE MANAGEMENT PLANNING RECOMMENDATIONS: Regional shoreline management plans (based on estuary, bay, or littoral cell) should be developed by local, state, and federal partners to address erosion on sheltered shorelines in a comprehensive, proactive manner. The plan should help reduce the inadvertent loss of recreational, aesthetic, economic, and ecological values of sheltered coastal areas. 20

21 UNDERSTANDING SHELTERED SHORELINE PROCESSES FINDING: The scope and accessibility of information regarding the causes of erosion at specific sites and the overall patterns of erosion and inundation in the broader region is insufficient to support development of an integrated plan for managing erosion. 21

22 UNDERSTANDING SHELTERED SHORELINE PROCESSES RECOMMENDATION: Federal and state agencies, and coastal counties and communities should support targeted studies of sheltered coast dynamics to provide an informed basis for selecting erosion mitigation options that consider the characteristics of the broader coastal system. 22

23 Improved Awareness of Options for Addressing Erosion FINDING: Decision-makers often do not have sufficient information about the mitigation options available to them or their short and long term impacts. 23

24 Improved Awareness of Options for Addressing Erosion RECOMMENDATION: A national dialogue should be initiated to develop guidelines for erosion control on sheltered coasts and to produce publications with objective information about erosion control technologies. 24

25 In Summary Landowners, contractors, local and state authorities often are unaware of the full suite of erosion mitigation strategies and their effectiveness; All mitigation measures affect ecosystem services; Individual decisions lead to cumulative impacts that could be avoided by local, proactive shoreline management plans Permitting systems should promote mitigation approaches that maintain more natural shorelines 25

26 Between low water and the flotsam and jetsam of the high-tide mark, land and sea wage a never-ending conflict for possession. Rachel Carson, Undersea The Atlantic Monthly, September 1937, the article that launched her career as a writer. 26