A soft berm is a nature-based solution in coastal management that uses soft engineering principles to work with the natural dynamics of the coast. This technique involves strategically placing large volumes of unconsolidated sediment, typically sand, onto an existing beach profile. The primary purpose of this constructed mound is to act as a sacrificial buffer, designed to absorb and dissipate the intense energy of waves and storm surges. Coastal managers implement this method to stabilize vulnerable shorelines, protect inland infrastructure, and maintain the ecological integrity of the beach environment.
The Definition and Structure of a Soft Berm
The term “soft” refers to the berm’s composition of loose, movable sediment like sand, gravel, or suitable fill material, distinguishing it from rigid structures such as seawalls. It is a component of a larger beach nourishment project, where material is added to widen the beach and build up a raised, sloping mound along the upper foreshore. This feature is characterized by a specific cross-section, including a relatively flat crest, which is the highest point, and a seaward slope that gradually descends toward the water.
The effectiveness of a soft berm is tied to its dynamic response to hydrodynamic forces, meaning it is designed to change shape during high-energy events. Unlike hardened structures, the soft berm is expected to erode and lose material during a storm, sacrificing itself to protect the landward environment. This temporary erosion and subsequent offshore deposition of material help stabilize the entire beach profile. As calmer conditions return, natural processes or subsequent nourishment efforts help restore the berm, maintaining the long-term integrity of the shoreline system.
Primary Functions in Coastal Protection
The main function of a soft berm is to serve as the first line of defense against destructive oceanic forces, particularly during storm events. This mound of sand dissipates wave energy by forcing waves to break further offshore and travel across a wider, shallower beach profile. The friction created by this extended shallow area reduces the velocity and destructive force of incoming waves before they reach the vulnerable parts of the coast.
This action directly contributes to erosion mitigation by acting as a substantial buffer zone. When waves hit the berm, the sacrificial sand volume is intentionally eroded instead of the native beach, dunes, or back-shore infrastructure. The volume of material provides a temporary reservoir that can be redistributed by the sea without permanently damaging the coastline.
Soft berms are instrumental in storm surge buffering, which is important during hurricanes or intense coastal storms. By increasing the elevation of the beach profile, the berm creates a higher barrier that slows the inland penetration of the elevated water level. This elevation gain reduces the duration and depth of inundation on the landward side, offering significant protection to properties and ecosystems. The berm’s ability to yield and absorb impact is an advantage over rigid defenses, which can sometimes worsen erosion on adjacent beaches.
Construction Methods and Material Selection
The construction of a soft berm is accomplished through beach nourishment, a process requiring careful planning and specialized heavy equipment. Material is often sourced from offshore borrow areas, where large volumes of compatible sand are extracted using hydraulic dredging vessels. This dredged material is then pumped ashore via pipelines or transported by barges and deposited directly onto the beach profile.
Once the material is placed, bulldozers and other earth-moving equipment grade and shape the sand into the designed berm profile, including the crest height and seaward slope angle. The selection of compatible sand is an engineering requirement, as it must closely match the grain size, color, and composition of the native beach sediment. Using material finer than the native sand can lead to rapid erosion, while coarser material may alter the beach ecology. Careful selection ensures the constructed berm remains stable and integrates smoothly with the existing coastal environment.
Environmental Considerations and Habitat Integration
Soft berms offer ecological advantages over traditional hard structures because they maintain the natural continuity and function of the beach ecosystem. By using natural sediment, the berm facilitates the continuation of natural processes, such as sand transport and the formation of new dunes on the landward side. This process is often enhanced by planting native, salt-tolerant vegetation, which helps trap windblown sand and stabilize the feature.
The restored beach platform and new dune areas can create or enhance habitat for various species, including nesting shorebirds, sea turtles, and specialized dune flora. Timing construction to avoid sensitive periods, such as turtle nesting seasons, is a standard practice to minimize environmental disruption. The use of soft engineering allows for an integrated approach to coastal defense, providing protection while supporting the biodiversity and natural resilience of the shoreline.