Barrier Beaches and Dunes
Performance Indicator Summary
Performance Indicator: Barrier Beaches and Dunes
Technical Workgroup: Coastal TWG
Researched by: Baird & Associates
Modeled by: Baird & Associates completed the modeling. No algorithm or economic calculations were developed for the FEPS due to the inability of modeling sandy shore evolution over very long time periods (i.e. 101 years). However, criteria were recommended based on the detailed storm modeling at Eastern Lake Ontario (see below).
Activity represented by this indicator: Barrier beaches and dunes protect many of the sheltered embayments and drowned river valleys along the shores of Lake Ontario, which in turn support the wetlands and estuaries that provide critical environmental habitat. Without these protective beaches, the wetlands and estuaries would be exposed to the full force of waves and storms on Lake Ontario. Exposure to storm waves would permanently alter the biological and ecological function of the habitat.
The barrier beach and sheltered bay of North Sandy Pond, Eastern Lake Ontario is presented below (orthophotograph and bathymetry). Although the location of the pond inlet has migrated along the barrier several times over the past last 100 years (as illustrated by the triangular and elongate sediment masses extending into the pond), the barrier has existed as a shoreline feature for a much longer time period. The barrier continues to shelter the pond and its critical environmental habitat.
Conversely, the remnants of the old barrier beach complex at Braddock's Bay, in Monroe County (south shore) are presented in the second aerial photograph below. With the exception of the
south-east section of the former barrier, which has been armored to stabilize the shoreline position and shelter the marina, the entire natural barrier beach has vanished. The reasons for the disappearance of this barrier beach system are complex (both human influences and natural processes) and are documented in the Detailed Study Sites Report (Baird, in preparation). However, what is important is the permanent and negative impact of the barrier beach loss on the wetland ecosystems of Braddocks Bay which were once sheltered from Lake Ontario waves.
In summary, barrier beaches and dunes provide critical natural protection by sheltering embayments and drowned river valleys from Lake Ontario waves. They are also used for recreation during the summer months.
Link to water level: The morphology and evolution of sand and gravel barrier beaches are influenced by water levels. For example, the combination of high lake levels and storms can lead to beach/dune erosion and even breaches in the barrier complex. If these types of impacts persist, they can ultimate affect the stability and presence of the barrier beach. Alternatively, during periods of low lake levels, beach width expands in front of the embryo dunes / foredune, increasing the potential for aeolian transport to re-nourish the dune system (i.e. wind blown sand). Cycles of lake levels are also important. For example, if a period of high lake levels occurs due to high net basin supplies, accelerated erosion would be expected. Therefore, it would be ideal if a period of lower lake levels followed to provide a recovery period for the beaches and dunes.
Baird completed detailed computer modeling in conjunction with the Environmental TWG to quantify the role of lake levels and storms on beach/dune erosion and more specifically, the potential for disruption of existing dune grass (Ammophila) environments, an endangered plant species (NYSDEC). The graphic below highlights the potential beach and dune erosion for a severe summer storm at high lake levels. A significant portion of the beach and dune erode during the storm. In locations were barrier beaches are narrow or feature low crested dunes, this type of erosion event could lead to more dramatic consequences, such as a breach in the barrier system.
Severe Summer Storm, South Barrier Profile, Photo 2080
Beach and Dune Erosion for the Aug 13-17, 1979 Storm
LO-6 Lake Level = 75.7 m (1.5 m)
Performance Indicator Metric: No metric was developed for this Performance Indicator. However, several recommendations were provided to existing Criteria developed by the Environmental TWG (coastal comments in blue):
Temporal validity: All seasons.
- LO-6) About once in every 25 years, and during periods of high supplies and lake levels, Lake Ontario shall be allowed to rise to between 75.30 m (247.05 ft) and 75.50 m (247.71 ft) for two consecutive quarter months to increase flooding of wetlands and destroy over-dominant wetland vegetation. Suggest that this criterion needs to be seasonal
(e.g. July-Aug.) when storm potential is minimal (CTWG, Jan 30, 2004) (Formerly criterion G)
- LO-7) About once in every 25 years, and during periods of low supplies and lake levels, peak annual Lake Ontario levels shall be allowed below 74.70 m (245.08 ft) to allow for the periodic drying of wetlands and to permit seed germination at lower elevations along the shore and allow the winter level to drop below 74.20 m (243.44 ft) to promote the building and rebuilding of barrier beaches and dunes. (Note the Coastal TWG suggested the lower winter level based on their work in late 2003). (Formerly criterion H)
Spatial validity: The results of the detailed computer modeling at Eastern Lake Ontario are representative for all natural barrier beach and dune complexes on Lake Ontario. Due to the geologic and physical conditions of the Upper St. Lawrence River System, the PI is not applicable to this portion of the study area.
Links with hydrology used to create the PI algorithm: No PI algorithm was developed.
The Algorithm: No PI algorithm was developed but modifications to criteria were provided (see above) to recognize the influence of water levels on barrier beaches and dunes.
Validation: The COSMOS model has been extensively tested and validated over the last 15 years. Numerous articles have been published in peer reviewed journals attesting to the accuracy and robustness of the COSMOS erosion predictions for sandy coastlines. We are confident that the results provide a reasonable indication of the erosion risk during high lake levels.
Documentation and References:
- Baird, (in preparation). Lake Ontario and Upper St. Lawrence River Detailed Study Sites. Prepared for the Coastal TWG
Risk and uncertainty assessment: There is very little uncertainty with the field data used or the numerical modeling techniques. However, since the characteristics of barrier beaches, such as sediment grain size, dune height and width, nearshore beach slope, exposure to lake waves and human influences vary around the lake, the results at Eastern Lake Ontario should be considered representative for other beaches on Lake Ontario, but not reflective of the exact response. For example, the magnitude of the erosion may be different at other locations due to site specific conditions.
See Excel document for graphics