High resolution and automated monitoring methodology (UAV) for vegetation and morphological dynamics involved in restoration projects in coastal sand dunes environments.

Abstract

Nowadays, given their fundamental importance, the application of coastal sand dunes’ restoration plans is widespread and they are usually aimed at reactivating the natural dynamics of two main components, often compromised: the morphological integrity and the vegetation growth. The aim of this work is to propose a relevant and low-cost methodology for monitoring this kind of restoration projects, which contemplates a simultaneous survey of the geomorphological component as well as the vegetational one. An Unmanned Aerial Vehicle (UAV) was applied to survey these two components’ trend, by means of building high‐resolution Digital Surfaces Models (DSMs) and RGB orthophotos, in an area in the North Adriatic Sea (Punta Marina, Ravenna, Italy): the local coastal environment is particularly suitable because it includes a residual coastal dune system, damaged by decades of erosion and fragmentation by human intervention. The are was recently the subject of a restoration project aimed at limiting its deterioration as well as enhancing dune stability by the construction of walkways and the introduction of vegetation. RGB data from the drone’s photographs were used to identify the spectral signature of vegetation in the visible part of the spectrum as well as that of bare sand. This allowed to monitor changes in the relative cover area extension (vegetated Vs not vegetated) in time. Elevation data from high‐resolution DSMs were used to identify and monitor changes (considering every source of error) of the principal morphological features, such as the Dune Foot Line (DFL), the Dune Crest Line (DCL), the Dune seaward Crest Line (DsCL) and the Stable Vegetation Line (SVL). Both morphological data, as well as orthophotos analysis, confirmed a constant and progressive increase of the vegetated cover area and consolidation of the dune system following the restoration project. The proposed survey protocol resulted to be rapid, low‐cost and easily replicable by coastal managers to quantify the effectiveness of restoration projects.