Beach Protection and Enhancement
Waves and wind move sand around throughout the year. Vegetation can provide stability and capture sand at the base of the plant to allow the surface to incrementally rise, one grain at a time. Dunes vegetated with beach grass act as a major sand storage area which replenish sand to eroded beaches during storm events. This hardy plant can tolerate high salinity concentrations, direct sun, extreme heat, lack of fertile soil, and fluctuating water supply. However, the rigid stems cannot survive being trampled by people or vehicles. Unlike plants that grow in richer soil, the roots are not what holds the material in place - it's the stems that catch the sand as it blows.
Protecting the dunes prevents loss of life and property during storms and protects the sand supply that slows shoreline erosion. Grasses that build up and anchor dunes help to prevent breaches, which allow floodwaters to channel inland during coastal storms and potentially cause property damage and safety risks. However, breaches are a natural occurrence, even on vegetated dunes. Maintaining a wide beach through beach nourishment is the best way to prevent breaches from forming.
Beach Grass Planting
Every spring since 1990, DNREC organized, volunteer supported, beach grass planting events have occurred resulting in more than 5 million stems of Cape American beach grass being planted along the ocean and bay beaches. Many factors go into determining how many stems of beach grass will be planted in a given year. For instance, storms can wash away previous years' plantings, increasing the likelihood of additional plantings, or result in extensive damage leaving conditions unsuitable for new plantings. Additionally, DNREC’s organized events can be affected by available funding and events held by other organizations that are not tracked by the department. Fewer plants are required for bay beaches because they typically have dunes that are not as large as ocean beaches and, therefore, less available space for planting.
Stems of Beach Grass Planted at Ocean and Bay Beaches
In an undisturbed environment, sand movement onto and off of the beach is a natural process that is always at work. Calmer waves during the summer months transport sand from offshore bars and the surf zone to the beach causing the beach to build up in height and width. Wind also blows sand inland onto the dunes where it is trapped by the vegetation and stored until it is removed by storms. In the winter storm season, beaches become narrow as waves carry and deposit sand offshore. The process of moving sand offshore creates sandbars and helps to dissipate the wave energy by causing the waves to break further away from the shoreline. In the summer, the gentler waves move the sand back onshore, creating a higher and wider beach.
The beach profile data below was collected by surveyors for one beach on the Delaware Bay and one beach on the Atlantic Ocean. The curves show the differences in the shape of the beach between winter and summer when the sand is moving between on and offshore with wave activity and storms. The Ocean beach has a steeper slope with more variation seasonally, whereas the Bay beach has a more gradual slope with subtle changes seasonally.
Ocean Beach: Herring Point 2015
Bay Beach: Bennetts Pier 2017
In a balanced system, the sand migration process repeats itself, naturally shifting the shores inward and back out over time. The reality is that beach environments are not undisturbed and these systems are not balanced. Over the years, development along the coast has inhibited the natural sand cycle and the migration of sand. This may cause problems as the sea level continues to rise and the beaches attempt to migrate inland, interfering with the built environment.
Page reviewed 7/22/19