USGS scientists have developed a new modeling approach, the Articulated Barrier Shoreface (ABSF) model, that shows how underwater features influence whether barrier islands persist—or disappear—over time.

Looking Beneath the Waves

A key but often overlooked part of the coastal system is the shoreface—the underwater zone extending from the beach to deeper waters where waves no longer move sediment. This region acts as a reservoir of sand that can be exchanged with the beach and dunes, especially during storms.

Until now, many models treated the shoreface as a single, uniform layer. The ABSF model breaks it into multiple interacting parts, allowing scientists to better simulate how sand moves between shallow and deeper regions.

Sand Supply Drives Survival

The study highlights two critical factors that determine how barrier islands respond to sea-level rise and storms: 

• Storm-driven sand transport: Strong storms can push sand from the shoreface onto the island, helping it maintain elevation.  

• Shoreface depth: Deeper shorefaces make it harder for sand to return to the beach system.

When these factors are favorable, barrier islands can “keep up” with rising seas by shifting landward and redistributing sand. But when they are not, sand fails to reach the islands, leading to a net loss of sediment.

Media

Sources/Usage: Public Domain. View Media Details

An Overlooked Lag Effect

One of the study’s most important findings is a kind of disconnect within the shoreface itself.

Changes in the deeper part of the shoreface occur more slowly than in the shallow region closer to shore. As sea levels rise, this lag can trap sand offshore—effectively stranding it beyond the reach of waves and storms that would normally move it back onto the island.

This stranded sand reduces the amount of material available to sustain beaches and dunes.

Faster Drowning Than Expected

Compared to older models, the ABSF approach suggests that barrier islands may drown more frequently and more quickly than previously predicted.

Without sufficient sand returning from the shoreface, islands lose their ability to maintain elevation and width. Over time, this can lead to increased overwash, fragmentation, and eventual submergence.

Why It Matters

Barrier islands protect coastal communities and ecosystems by absorbing wave energy and storm surge. Understanding the processes that control their stability is essential for: