Shoreline Management Model – SMM

A GIS spatial model that determines appropriate shoreline best management practices using available spatial data and decision tree logic.  SMM flow diagram (.pdf)

The model output of preferred shoreline practices is based on available spatial data for shoreline conditions, including:

  • Bank vegetation cover & bank height
  • Presence or absence of natural buffers – tidal marshes, beaches, riparian forests
  • Nearshore water depth
  • Wave exposure (fetch)
  • Proximity of coastal development to the shoreline  

The model output for shoreline best management practices is displayed in each locality's Comprehensive Map Viewer.  GIS shapefiles from the SMM are also available for downloading from within each locality portal.

Shoreline Best Management Practice Classifications
Land Use Management

Where bank and/or shoreline approaches are extremely difficult to implement or limited in effectiveness due to existing land use conditions; reduce risk by modifying the upland land use. This may include relocating or elevating buildings, utilities, and other infrastructure and/or managing stormwater. All new construction should be located 100 feet or more from the top of bank. Actions may also include requesting zoning variances for relief from setback and other land use requirements or restrictions that may increase erosion risk. 

Maintain - Enhance - Restore Riparian Buffer

Provide stabilization through maintaining, enhancing, or restoring the vegetation in the riparian buffer. The target area for riparian buffer should extend 100 feet back from the top of bank. Preferred approaches for riparian buffer management may include one or a combination of the following: Preserve existing riparian vegetation in the buffer area; manage vegetative cover by selectively removing and/or pruning dead, dying, and severely leaning trees as necessary; enhance the riparian area by planting appropriate vegetation or allowing for natural regeneration of small native trees and shrubs; replace waterfront lawns with a variety of native deep-rooted grasses, shrubs, and small trees and; remove invasive species, if present, and replace with native vegetation.

Along some shorelines, it may be appropriate to reduce the steepness of the bank slope to allow wave run-up and to improve growing conditions in order to sustain vegetation. Grading should only be conducted where essential and done as minimally as possible to achieve the necessary slope. Banks that are graded should be stabilized with a variety of native plants placed at appropriate elevations. The feasibility to grade a bank may be limited by upland structures, existing shoreline defense structures, and/or adjacent property conditions. In certain cases, it may be beneficial to the tidal wetland ecosystem to remove existing structures, if possible, to achieve a properly graded and vegetated bank.

Maintain - Enhance - Create Marsh

Includes sand fill and fiber coir logs-mats

Provide stabilization through marsh vegetation; the target area for marsh buffer should extend from mid-tide to an elevation 1.5 times the tide range above mean low water (the upper limit of which may be observed by the presence of upland vegetation) , with wetland vegetation planted at appropriate elevations.

Preferred approaches for marsh buffer management may include one or a combination of the following: Provide or enhance wave attenuation by maintaining or widening existing marsh or planting new marsh which may require the placement of sand fill and/or fiber logs. Encourage both low and high marsh areas.  Periodically monitor marsh for signs of damage and dead plants, especially after a storm and after installation. Marsh that is designed to allow for landward migration is preferred in order to accommodate sea level rise.  A channelward design usually requires sand fill to create suitable elevations. Marsh management includes avoidance of using herbicides near marsh.

Along some shorelines, it may be appropriate to reduce the steepness of the bank slope to allow wave run-up and to improve growing conditions in order to sustain vegetation. Grading should only be conducted where essential and done as minimally as possible to achieve the necessary slope. Banks that are graded should be stabilized with a variety of native plants placed at appropriate elevations. The feasibility to grade a bank may be limited by upland structures, existing shoreline defense structures, and/or adjacent property conditions. In certain cases, it may be beneficial to the tidal wetland ecosystem to remove existing structures, if possible, to achieve a properly graded and vegetated bank.

Plant Marsh with Sill

Plant tidal marsh (or maintain/widen existing marsh) and construct a rock sill placed offshore from the marsh. The site-specific suitability for a sill must be determined, including bottom hardness, navigation conflicts, construction access limitations, orientation and available sunlight for marsh plants. If existing marsh is greater than 15 ft. wide, consider placing sill just offshore from marsh edge. If existing marsh is less than 15 ft. wide or absent, consider widening marsh by grading bank landward to accommodate sea level rise and/or providing sand fill channelward to increase marsh width and/or elevation and placing sill just offshore new marsh edge.

Maintain Beach OR Offshore Breakwaters with Beach Nourishment

Preserve existing wide sand beach if present, allow for dynamic sand movement for protection; nourish the beach by placing good quality sand along the beach shoreline that is similar to the native sand.

Use offshore breakwaters with beach nourishment only where additional protection is necessary.  These are a series of large rock structures placed strategically offshore to maintain stable pocket beaches between the structures.  The wide beaches provide most of the protection, so beach nourishment should be included; periodic beach re-nourishment may be needed.  The site-specific suitability for offshore breakwaters with beach nourishment must be determined, seek expert advice.

Groin Field with Beach Nourishment

A series of several groins built parallel to each other along a beach shoreline. Established groin fields with wide beaches can be maintained with periodic beach nourishment; repair and replace individual groins as needed. 

Revetment

A sloped structure constructed usually with riprap placed against the upland bank for erosion control. The size of a revetment should be determined by the wave height expected to strike the shoreline. The site-suitability for a revetment must be determined, including bank condition, tidal marsh presence, and construction access limitations.   

Areas of Special Concern

Marinas – Canals – Industrial or Commercial with bulkhead or wharf – Other Unique Local Features, e.g. developed marsh & barrier islands 

The preferred shoreline best management practices within Areas of Special Concern will depend on the need for and limitations posed by navigation access or unique developed areas.  Vegetation buffers should be included where possible.  Revetments are preferred where erosion protection is necessary.  Bulkheads should be limited to restricted navigation areas.  Bulkhead replacement should be in same alignment or landward from original bulkhead.

No Action Needed

No specific actions are suitable for shoreline protection, e.g. boat ramps, undeveloped marsh and barrier islands.

Choosing the most effective yet least impacting shoreline practice requires consideration of multiple environmental and socio-economic factors.  Spatial data are not readily available or up to date for some of these relevant shoreline conditions.  For example, the model does not include the presence of submerged aquatic vegetation (SAV), endangered or threatened species, and significant shellfish habitat.  Other site conditions not always included in the model output are existing shoreline defense structures, lot size and shoreline length, the proximity of buildings or other infrastructure to the shoreline, and recreation and navigation use conflicts. 

For more explicit, on-site decision making refer to the Self-Guided Decision Tools.  Like the Shoreline Management Model, these tools lead users through a series of questions about shoreline characteristics and result in recommendations for environmentally preferable shoreline management practices.