An evolutionary categorisation model for backbarrier environments

Shorelines occurring along restricted fetch environments, such as the backsides of barrier islands, are extremely diverse with respect to their morphologic characteristics and evolution. In order to better understand the morphodynamic evolution of backbarriers and the associated implications for entire barrier systems, this study proposes a backbarrier evolutionary categorisation model based on the development of two types of index: backbarrier evolution tendency and backbarrier maturation condition. The proposed characterisation system is applied to the Ria Formosa backbarrier (located in southern Portugal) for the period 1947 to 2001. Cross-shore and longshore backbarrier trends in Ria Formosa suggest a shrinking of the lagoon system as a consequence of a decrease in the coastal length of the backbarrier coastline and a landward displacement of it. Even though some of the backbarriers examined were found to be in an immature state, the results obtained illustrate a maturing trend for the system overall. Barriers in Ria Formosa fall into two main evolutionary categories: backbarrier reduction and backbarrier growth. This means that neither smoothing nor branching has been significant and therefore that backbarrier recent evolution is closely related to barrier coast length. Application of the proposed characterisation to the Ria Formosa case study has helped reveal backbarrier evolutionary trends and therefore should be of use in the management of backbarrier systems. (C) 2008 Elsevier B.V. All rights reserved.