# Unforeseen cascading effects of an inlet opening

## TL;DR

Opening an inlet in Portugal caused unexpected coastal changes, risking a historic site and nearby settlement.

## Contribution

The study reveals a new cascading effect of inlet opening on coastal dynamics and heritage preservation.

## Key findings

- The inlet opening accelerated lagoon margin retreat from 0.2 to 2 meters per year.
- A medieval fortress and settlement may be at risk due to reactivation of an old cliff.
- Coastal management measures are needed to prevent damage to a protected area.

## Abstract

The opening of the Cacela Inlet (southern Portugal) in 2010 led to unforeseen effects observed after 2017, including an extreme acceleration of the retreat of the inland lagoon margin from about 0.2 to 2 m/year. This was a consequence of the development of a large flood delta in an area of limited accommodation space, forcing the main tidal channel to move inland. The coastal retreat currently affects a flat sandy area that separates the old and inactive Cacela cliff from the lagoon. Between 2035 and 2040, the currently inactive Cacela cliff is likely to become active again, posing a potential risk of damage to a medieval fortress and the existing settlement of Cacela Velha, an unforeseen cascading effect of the opening of the inlet. In order to prevent instability and damage to this legally protected area of national and public interest, several coastal management measures will be required.