Riduzione del trasporto solido fluviale e modificazioni della linea di riva tra le foci del Vomano e del Pescara: trend storico recente

Abstract

Manzo C.: Reduction of river sediment transport and shoreline modifications between vomano and pescara river mouths:
late historical trend (IT ISSN 0394-3356, 2008).
The main purpose of the study is the coastline evolution analysis of the stretch situated between Vomano and Pescara river outlets
(middle Adriatic Sea, Abruzzo, Italy), focusing on the relationships between river sediment transport and coastline evolution.
Many Authors suggest that erosion in the middle Adriatic area mainly took place on the river deltas as an effect of sedimentary deficit
due to human activities in the river basins. The present work confirm such a description, highlighting the relationships of coastal evolution both to social-economic aspects (impact of human activities in the river basins) and to climate (variability of annual rainfall).
Leaving out a detailed characterizations of some important factors conditioning coastal dynamics, such as wave motion, bathymetry
and physical-sedimentological properties of the beach, the study is focused on the planform analysis of subsequent coastlines shapes
and positions.
Historical maps and aerial photographs covering the last two centuries were georeferenced with the aim to reconstruct a time series of
multiple shoreline positions. Therefore the course of sedimentary budget was obtained multiplying the rate of coastal area variation by
the depth of appreciable send movement.
In the first part of XIX century the coastline appeared quite rectified with small delta cusps protrusion. The second half of the XIX century reveals high delta protrusion and high sedimentary budgets. This trend became to change at the beginnings of XX century with the increment of human activities in the river basins: the sedimentary budget was about zero from 1920 till 1940 and it tends to become quite constant negative beginning from 1940, with strong erosion of river deltas.
Such long-term trend allowed to implement a simplified one-line model, with the aim to identify a general coastal behaviour related to
river inputs and seaward sedimentary losses. The model used is based on a finite differences solution of the diffusivity differential
equation, describing the shoreline variations vs. time.
A back analysis was made in order to get the best fitting of the phenomenon, using the sedimentary balance and the time series of
multiple shoreline positions as the input calibrating information. Assuming that the rate of sedimentary balance will remain constant,
the future scenario predicted by the model reveal that erosion will tend to involve more and more sectors progressively. Even if such
simplified model is not completely realistic, it seems to be a successful balance between realism and practicality, it can direct further
studies and observations and help to critically test hypothesis. Actually the results are partially observable.
Such results show a conceptual model which should lead to further studies, though it can be considered a contribution to the comprehension of behaviour of this coastal tract, whose dynamics are strongly related to river sediment transport.