Vegetated Terraces: Flood Adaptation Measure


Section diagram of vegetated terrace. ©CMG



ECOLOGICAL INFRASTRUCTURE
WATER LEVEL RANGE: Intertidal to supratidal

SHORELINE LOCATION: Shoreline



DESIGN LIFE
ADAPTABILITY
IMPACT ON THE WATERFRONT
CONSTRUCTION COST
50+ years
Medium
Minor Intervention
TBD


COASTAL FLOOD HAZARDS MITIGATED:
Enhancements can provide flood protection when combined with other physical infrastructure
Sea Level Rise
Storm Surge
Groundwater
Waves
Erosion


MEASURES COMPATIBILITY
ECOSYSTEM SERVICES: Measure may affect these shoreline values
Flood
Seismic
Seawalls, Levees, Revetments
All
Aquatic Habitat
Terrestrial Habitat
Water Quality
Carbon Storage


DESCRIPTION:
Vegetated terraces are the modification of existing slopes, or construction of new stepped slopes, to include vegetated surfaces. The slopes can be stepped back or stepped forward, and species can be planted or allowed to develop spontaneously on the terraces. Vegetated terraces can provide a reduction in wave runup and overtopping, thereby mitigating flooding and erosion.


CONSIDERATIONS:
ADVANTAGES:
DISADVANTAGES:
  • Vegetated terraces can be built to a height to protect against storm surge, wave hazards, and sea level rise, depending on water level and wave conditions. They cannot tolerate high wave energy. These factors, as well as the tidal range, must be considered to design suitable habitat for plant growth and mitigate flooding.
  • Habitat creation by vegetation growth.
  • Vegetation type can adapt over time to long-term changes in water elevations.
  • Mitigates erosion
  • Flexible design
  • Lifetime of structures 50+ years
  • Can be designed to accommodate a range of water levels and wave conditions
  • Compatible with structural and nature-based flood mitigation measures
  • Requires large horizontal extent and potential encroachment into water
  • Difficult to adapt to higher water levels once constructed
  • Can collect floating debris
  • Not suitable for high wave energy environments
  • Lifetime of vegetation will depend on species selected, climate, and water quality
  • Seismic performance depends on foundation and construction


CONSTRUCTION IMPACTS TO THE PUBLIC:
SEA LEVEL RISE ADAPTATION OPPORTUNITIES:
CASE STUDIES:
  • Landside access necessary. Access to the shoreline will be constricted due to construction, and may impact parts of the Promenade.
  • Can be designed to accommodate a range of water levels and wave conditions, but once built, significant modification would be required to accommodate higher water levels or wave conditions.
  • None cited


DESIGN OPPORTUNITIES:
Ecological Enhancements
Urban Design
Form
  • Measure is compatible with nature-based flood mitigation measures and increases biodiversity and marine habitatDesign of terraces can integrate with structural measure opportunities, and provide new ways of experiencing the waterfront and shoreline ecology.
  • Design of terraces can integrate with structural measure opportunities, and provide new ways of experiencing the waterfront and shoreline ecology.
  • Stepped form is adaptable to structural modifications and urban design goals.


DESIGN CONSIDERATIONS:

  • Need to be developed on a site-specific basis, constructed with ecological materials, and planted with native species. Ideally suited for sheltered areas with relatively low wave action, otherwise vegetation may not survive and terraces can be eroded.
  • Wave conditions, tidal range, and sea level rise need to be considered to ensure the survival of planted species as well as their adaptation to future sea levels.
  • Wind and waves may cause floating debris to collect on terraces.

HISTORICAL RESOURCE CONSIDERATIONS:

  • Siting needs to consider impacts to historical sites or and should consider access.

SITE-SPECIFIC CONSIDERATIONS:

  • Geotechnical conditions must be considered.

URBAN DESIGN CONSIDERATIONS:

  • Can include pedestrian walkways and bike trails.
  • Depending on the height of the structure required to address wave hazards, may provide opportunity for Bay views and Bay access

INSTALLATION AND CONSTRUCTABILITY CONSIDERATIONS:

  • Land-based equipment and delivery of materials will require landside access. New terraces may require significant grading/soil preparation.

OPERATIONS AND MAINTENANCE CONSIDERATIONS:

  • Periodic inspections and maintenance, as necessary, would be required to maintain flood protection capacity.


Download the Vegetated Terraces Factsheet.

Learn about other types of measures from our Measures Explorer page.



Section diagram of vegetated terrace. ©CMG



ECOLOGICAL INFRASTRUCTURE
WATER LEVEL RANGE: Intertidal to supratidal

SHORELINE LOCATION: Shoreline



DESIGN LIFE
ADAPTABILITY
IMPACT ON THE WATERFRONT
CONSTRUCTION COST
50+ years
Medium
Minor Intervention
TBD


COASTAL FLOOD HAZARDS MITIGATED:
Enhancements can provide flood protection when combined with other physical infrastructure
Sea Level Rise
Storm Surge
Groundwater
Waves
Erosion


MEASURES COMPATIBILITY
ECOSYSTEM SERVICES: Measure may affect these shoreline values
Flood
Seismic
Seawalls, Levees, Revetments
All
Aquatic Habitat
Terrestrial Habitat
Water Quality
Carbon Storage


DESCRIPTION:
Vegetated terraces are the modification of existing slopes, or construction of new stepped slopes, to include vegetated surfaces. The slopes can be stepped back or stepped forward, and species can be planted or allowed to develop spontaneously on the terraces. Vegetated terraces can provide a reduction in wave runup and overtopping, thereby mitigating flooding and erosion.


CONSIDERATIONS:
ADVANTAGES:
DISADVANTAGES:
  • Vegetated terraces can be built to a height to protect against storm surge, wave hazards, and sea level rise, depending on water level and wave conditions. They cannot tolerate high wave energy. These factors, as well as the tidal range, must be considered to design suitable habitat for plant growth and mitigate flooding.
  • Habitat creation by vegetation growth.
  • Vegetation type can adapt over time to long-term changes in water elevations.
  • Mitigates erosion
  • Flexible design
  • Lifetime of structures 50+ years
  • Can be designed to accommodate a range of water levels and wave conditions
  • Compatible with structural and nature-based flood mitigation measures
  • Requires large horizontal extent and potential encroachment into water
  • Difficult to adapt to higher water levels once constructed
  • Can collect floating debris
  • Not suitable for high wave energy environments
  • Lifetime of vegetation will depend on species selected, climate, and water quality
  • Seismic performance depends on foundation and construction


CONSTRUCTION IMPACTS TO THE PUBLIC:
SEA LEVEL RISE ADAPTATION OPPORTUNITIES:
CASE STUDIES:
  • Landside access necessary. Access to the shoreline will be constricted due to construction, and may impact parts of the Promenade.
  • Can be designed to accommodate a range of water levels and wave conditions, but once built, significant modification would be required to accommodate higher water levels or wave conditions.
  • None cited


DESIGN OPPORTUNITIES:
Ecological Enhancements
Urban Design
Form
  • Measure is compatible with nature-based flood mitigation measures and increases biodiversity and marine habitatDesign of terraces can integrate with structural measure opportunities, and provide new ways of experiencing the waterfront and shoreline ecology.
  • Design of terraces can integrate with structural measure opportunities, and provide new ways of experiencing the waterfront and shoreline ecology.
  • Stepped form is adaptable to structural modifications and urban design goals.


DESIGN CONSIDERATIONS:

  • Need to be developed on a site-specific basis, constructed with ecological materials, and planted with native species. Ideally suited for sheltered areas with relatively low wave action, otherwise vegetation may not survive and terraces can be eroded.
  • Wave conditions, tidal range, and sea level rise need to be considered to ensure the survival of planted species as well as their adaptation to future sea levels.
  • Wind and waves may cause floating debris to collect on terraces.

HISTORICAL RESOURCE CONSIDERATIONS:

  • Siting needs to consider impacts to historical sites or and should consider access.

SITE-SPECIFIC CONSIDERATIONS:

  • Geotechnical conditions must be considered.

URBAN DESIGN CONSIDERATIONS:

  • Can include pedestrian walkways and bike trails.
  • Depending on the height of the structure required to address wave hazards, may provide opportunity for Bay views and Bay access

INSTALLATION AND CONSTRUCTABILITY CONSIDERATIONS:

  • Land-based equipment and delivery of materials will require landside access. New terraces may require significant grading/soil preparation.

OPERATIONS AND MAINTENANCE CONSIDERATIONS:

  • Periodic inspections and maintenance, as necessary, would be required to maintain flood protection capacity.


Download the Vegetated Terraces Factsheet.

Learn about other types of measures from our Measures Explorer page.