ETD system

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Tesi etd-04062018-221131


Thesis type
Tesi di dottorato di ricerca
Author
MAMMI, IRENE MARIA
URN
etd-04062018-221131
Title
Morphodynamics at the Ombrone River delta during erosional and depositional phases in historical times
Settore scientifico disciplinare
GEO/04
Corso di studi
SCIENZE DELLA TERRA
Commissione
tutor Prof. Pranzini, Enzo
Parole chiave
  • evolution pattern
  • beach ridges
  • erosion and depositional phases
  • River delta
Data inizio appello
13/04/2018;
Consultabilità
parziale
Data di rilascio
13/04/2021
Riassunto analitico
The important contribution on understanding River deltas allowed us the awareness that these areas and the related morphologies (i.e. beach ridges for a wave dominated delta) assume a growing importance to reading anthropic and natural changes. <br>We know the importance of the River deltas under the economic aspect as well as the natural and ecological. Beach ridges represent important morphologies for the dynamic balance of these systems, also playing a fundamental role in the protection of these fragile environments.<br>The aim of this work is to identify the evolutionary trends of the Ombrone River delta, located in south Tuscany, mainly considering the morphological variations of the beach ridges that are supposed to approximate the ancient shorelines. <br>The purpose of this research was orientated to obtain a better understanding of the dynamics of the delta in its phases of erosion and progradation during the historical time and in particular try to distinguish, always through the study of morphological elements, the presence of any changes in the direction of the longshore transport.<br>The study area covers almost entirely the Maremma Regional Park, characterized by high naturalistic value, which over time has undergone important variations in the shoreline position alternating periods of great advancement to erosion. These, according to a wide bibliographic review, may be attributed to the strong demographic development and the cultivation of large areas, placed within the hydrographic basin, that determined a widespread soil erosion and the consequent increase of the solid transport by rivers.<br>The present work arises to study in detail all the historical phases that have characterized the evolution of the Ombrone river delta trying to distinguish, by studying the beach ridges and other morphological indicators, those phases of erosion and progradation. Indeed, the morphological and sedimentological evolution of wave dominated delta is often associated with deposits as spit, beach ridges, barrier islands and sandbars; these are often used as geomorphological indicators to determine the predominant direction of longshore transport to understand the mechanisms of the present and past coastal dynamic. <br>The aim of our research is also to put on evidence the beach ridges profiles variation, both in the area near the river mouth than in the delta wings, subdividing the delta in two dynamic systems deeply connected to each other which depend on the interaction with the wave climate and the river transport.<br>The main focus of this study are beach ridges, considered not as an isolated element but as a whole of a dynamic and complex system. Their balance involving many components like the waves characteristics, changes of river input and the variations of the beach and the shoreline.<br>The first part has involved to study of the evolution of the wave dominated delta, in particular by means of numerical modeling. Afterward we focused on the acquisition of the historical maps and satellite images processed by software such as GIS and ENVI for the last ones. It has been carried out the map of all the beach ridges present in the study area using various remote sensing techniques and data, active and passive. The shoreline changes were calculated for all the considered period and, through the study of their geometrical patterns, it was possible to define the historical evolutionary trends of the delta system. <br>Finally, we estimated the variation of the historical longshore transport by a here developed method regarding the angles formed by a deep water waves with the coastline.<br>The final goal reached was to contribute to the acknowledgement of the dynamics of the Ombrone River delta and, starting from the single components of this complex system, we provided useful indications of the characteristic phases of this site also indicating the direction of longshore transportation variations in the past.<br><br>
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