Stepped Slopes: Flood Adaptation Measure


Avila Beach, California ©RRM Design Group
(Claudio Fassardi with Jacobs can provide further contact if needed)



ECOLOGICAL INFRASTRUCTURE
WATER LEVEL RANGE: Intertidal to supratidal

SHORELINE LOCATION: Shoreline



DESIGN LIFE
ADAPTABILITY
IMPACT ON THE WATERFRONT
CONSTRUCTION COST
Decades
Medium
Major 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
N/A
Aquatic Habitat
Terrestrial Habitat
Water Quality
Carbon Storage
/


DESCRIPTION:
Stepped slopes can offer a visually attractive alternative to more traditional types of revetments. Constructed at the water edge, they can provide public access to the water and backshore erosion protection. Steps act as large roughness elements and, depending on design, can be comparable to or better than traditional rip-rap for reducing wave runup and overtopping. Compared to rip-rap revetments, stepped slopes are more expensive and can be prone to damage due to differential settlement and erosion of the toe.


CONSIDERATIONS:
ADVANTAGES:
DISADVANTAGES:
  • Should be designed to account for future anticipated sea level rise.
  • Waves can scour and erode toe if not properly buried. Best performance and longevity in low wave energy environments.
  • Consideration should be given to geotechnical, seismic, wave, and water level conditions.
  • Provides public access to the water
  • Aesthetically attractive
  • Steps act as large roughness elements which may reduce flooding due to wave overtopping
  • Flexible design can accommodate a wide variety of step shapes and elevations
  • High cost
  • Susceptible to damage due to differential settlement
  • Reduced habitat value
  • Because maintenance is required to remove marine growth in intertidal steps, preferable at small tide range and low wave activity locations
  • Limited adaptability to higher than design water levels



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.
  • Functional within a wide range of water levels, but once built limited adaptability to water level higher than design.
  • None cited


DESIGN OPPORTUNITIES:
Ecological Enhancements
Urban Design
Form
  • Opportunity to encourage habitat growth using ecological concrete where public access is restricted. Vegetation and terrestrial habitat can be incorporated in planters.
  • Given sufficient safety precautions, stepped slopes can be incorporated into other flood mitigation measures at the shoreline to enhance public access to the bay
  • Design is flexible and can accommodate a wide variety of step shapes and elevations, plus other amenities like benches, planters, etc.


DESIGN CONSIDERATIONS:

  • Requires a good foundation to prevent damage due to differential settlement.
  • Toe should be sufficiently buried and/or otherwise protected to prevent erosion of fill due to wave scour.

HISTORICAL RESOURCE CONSIDERATIONS:

  • Should not obstruct access or views to historic structures and be compatible with the character of the structure.

SITE-SPECIFIC CONSIDERATIONS:

  • Waves, water levels, geotechnical, seismic and propeller wash conditions.

URBAN DESIGN CONSIDERATIONS:

  • Will attract users close to the water’s edge. Hazardous activities need to be prevented.
  • For areas with beach access, can provide areas for people to sit or place belongings out of the sand.

INSTALLATION AND CONSTRUCTABILITY CONSIDERATIONS:

  • Steps can be fabricated offsite or poured in place.
  • Requires grading of existing soil.
  • Fill should be well compacted.
  • Requires a stable foundation to prevent failure due to differential settlement.

OPERATIONS AND MAINTENANCE CONSIDERATIONS:

  • Operation needs are generally low and depend on public use. Maintenance required to remove marine growth in intertidal steps.


Download the Stepped Slopes Walls Factsheet.

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



Avila Beach, California ©RRM Design Group
(Claudio Fassardi with Jacobs can provide further contact if needed)



ECOLOGICAL INFRASTRUCTURE
WATER LEVEL RANGE: Intertidal to supratidal

SHORELINE LOCATION: Shoreline



DESIGN LIFE
ADAPTABILITY
IMPACT ON THE WATERFRONT
CONSTRUCTION COST
Decades
Medium
Major 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
N/A
Aquatic Habitat
Terrestrial Habitat
Water Quality
Carbon Storage
/


DESCRIPTION:
Stepped slopes can offer a visually attractive alternative to more traditional types of revetments. Constructed at the water edge, they can provide public access to the water and backshore erosion protection. Steps act as large roughness elements and, depending on design, can be comparable to or better than traditional rip-rap for reducing wave runup and overtopping. Compared to rip-rap revetments, stepped slopes are more expensive and can be prone to damage due to differential settlement and erosion of the toe.


CONSIDERATIONS:
ADVANTAGES:
DISADVANTAGES:
  • Should be designed to account for future anticipated sea level rise.
  • Waves can scour and erode toe if not properly buried. Best performance and longevity in low wave energy environments.
  • Consideration should be given to geotechnical, seismic, wave, and water level conditions.
  • Provides public access to the water
  • Aesthetically attractive
  • Steps act as large roughness elements which may reduce flooding due to wave overtopping
  • Flexible design can accommodate a wide variety of step shapes and elevations
  • High cost
  • Susceptible to damage due to differential settlement
  • Reduced habitat value
  • Because maintenance is required to remove marine growth in intertidal steps, preferable at small tide range and low wave activity locations
  • Limited adaptability to higher than design water levels



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.
  • Functional within a wide range of water levels, but once built limited adaptability to water level higher than design.
  • None cited


DESIGN OPPORTUNITIES:
Ecological Enhancements
Urban Design
Form
  • Opportunity to encourage habitat growth using ecological concrete where public access is restricted. Vegetation and terrestrial habitat can be incorporated in planters.
  • Given sufficient safety precautions, stepped slopes can be incorporated into other flood mitigation measures at the shoreline to enhance public access to the bay
  • Design is flexible and can accommodate a wide variety of step shapes and elevations, plus other amenities like benches, planters, etc.


DESIGN CONSIDERATIONS:

  • Requires a good foundation to prevent damage due to differential settlement.
  • Toe should be sufficiently buried and/or otherwise protected to prevent erosion of fill due to wave scour.

HISTORICAL RESOURCE CONSIDERATIONS:

  • Should not obstruct access or views to historic structures and be compatible with the character of the structure.

SITE-SPECIFIC CONSIDERATIONS:

  • Waves, water levels, geotechnical, seismic and propeller wash conditions.

URBAN DESIGN CONSIDERATIONS:

  • Will attract users close to the water’s edge. Hazardous activities need to be prevented.
  • For areas with beach access, can provide areas for people to sit or place belongings out of the sand.

INSTALLATION AND CONSTRUCTABILITY CONSIDERATIONS:

  • Steps can be fabricated offsite or poured in place.
  • Requires grading of existing soil.
  • Fill should be well compacted.
  • Requires a stable foundation to prevent failure due to differential settlement.

OPERATIONS AND MAINTENANCE CONSIDERATIONS:

  • Operation needs are generally low and depend on public use. Maintenance required to remove marine growth in intertidal steps.


Download the Stepped Slopes Walls Factsheet.

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