Probabilistic Tsunami Hazard Assessment in Meso and Macro Tidal Areas. Application to the Cádiz Bay, Spain

Tsunami hazard can be analyzed from both deterministic and probabilistic points of view. The deterministic approach is based on a “credible” worst case tsunami, which is often selected from historical events in the region of study. Within the probabilistic approach (PTHA, Probabilistic Tsunami Hazard Analysis), statistical analysis can be carried out in particular regions where historical records of tsunami heights and runup are available. In areas where these historical records are scarce, synthetic series of events are usually generated using Monte Carlo approaches. Commonly, the sea level variation and the currents forced by the tidal motion are either disregarded or considered and treated as aleatory uncertainties in the numerical models. However, in zones with a macro and meso tidal regime, the effect of the tides on the probability distribution of tsunami hazard can be highly important. In this work, we present a PTHA methodology based on the generation of synthetic seismic catalogs and the incorporation of the sea level variation into a Monte Carlo simulation. We applied this methodology to the Bay of Cádiz area in Spain, a zone that was greatly damaged by the 1755 earthquake and tsunami. We build a database of tsunami numerical simulations for different variables: faults, earthquake magnitudes, epicenter locations and sea levels. From this database we generate a set of scenarios from the synthetic seismic catalogs and tidal conditions based on the probabilistic distribution of the involved variables. These scenarios cover the entire range of possible tsunami events in the synthetic catalog (earthquakes and sea levels). Each tsunami scenario is propagated using the tsunami numerical model C3, from the source region to the target coast (Cádiz Bay). Finally, we map the maximum values for a given probability of the selected variables (tsunami intensity measures) producing a set of thematic hazard maps. 1000 different time series of combined tsunamigenic earthquakes and tidal levels were synthetically generated using the Monte Carlo technique. Each time series had a 10000-year duration. The tsunami characteristics were statistically analyzed to derive different thematic maps for the return periods of 500, 1000, 5000, and 10000 years, including the maximum wave elevation, the maximum current speed, the maximum Froude number, and the maximum total forces.

Fortificazioni della Tunisia contese tra Spagnoli e Turchi a metà del secolo XVI, documentate dall’iconografia coeva. Un’analisi dal ter-ritorio all’architettura

Tunisian fortifications disputed between Spaniards and Turks in the mid-sixteenth century, documented by coeval iconography. An analysis from the territory to the architectureThe five volumes of the precious archival collection of drawings called Architettura Militare (Military Architecture), kept at the Archivio di Stato di Torino (Turin State Archive), propose documents made mostly by military engineers from the half of the sixteenth to the following first decade. The tomes collect mostly drawings of places under the aegis of the Duchy of Savoy, apart from the second one, dedicated to documents of Spanish military interest (Mediterranean Sea and Lombardy maps). As I pointed out at Fortmed Convention 2018, the reason why these documents are kept at the Turin State Archives is because of their belonging to Catherine of Aragon, daughter of the Spanish king and wife of Carlo Emanuele I di Savoia. In the volume Architettura Militare II (Military Architecture II) 26 tables, all datable from 1522 (Rhodes) to 1596 (Cadiz), concern territories, walled cities and fortifications, of islands and Mediterranean coasts, disputed by Christians and Turks for the supremacy on the sea. In the previous study I had examined drawings about Egypt, eastern Ottoman territories and Holy Land coasts, Spanish possessions as Perpignan and Cadiz bay. In this new study instead, I would like to examine in depth the iconography about Tunisia. Those drawings, so different from each other for scale and graphic quality, document those phases in which the Spanish control is characterized by alternate situations: the Iberian presidio dates back to 1535, reconquered by Ottomans in 1570, it is taken back in three years by Christians who keep it until 1574 only, when the whole Tunisian territory, precious bastion for the control of routes and trades, definitely returns in the hands of the Turks.

Beyond Human Interventions on Complex Bays: Effects on Water and Wave Dynamics (Study Case Cádiz Bay, Spain)

Bays are coastal environments with significant socio-economic importance, which has led to the development of human interventions in their interior that can have an important impact on the water and wave dynamics, which in turn modify their morphodynamics and water renewal capacity. In order to deepen our understanding of these impacts, numerical modeling was used in a bay in southern Spain to analyze the effect of inner harbor expansion and channel deepening, including the baroclinic and wave propagation effects, as well as variations in salinity and temperature. The results show that the deepening of the channel decreases the amplitude and speed of the tidal wave as it propagates through the bay, reducing the effects of friction and increasing the flushing time. The system evolves from convergent to a damping system that can potentially reduce the effects produced by projected sea level rise. In addition, the seasonal variability of salinity and temperature is reduced, increasing the bed shear stresses and resulting in increased turbidity that can affect the biogeochemistry of the bay. Finally, wave heights decrease along the main waterway, although the yearly-average wave energy flux is only slightly modified on the interior beaches of the bay. However, significant variations are observed during storms, which could affect the morphodynamics of these beaches.

Natural and Human-Induced Flow and Sediment Transport within Tidal Creek Networks Influenced by Ocean-Bay Tides

Improving current understanding of hydrodynamics and sediment dynamics in complex tidal embayments is of major importance to face future challenges derived from climate change and increasing human pressure. This work deepens the knowledge of the hydro-morphodynamics of complex creek networks that connect basins with different characteristics, identifying their morphodynamic trends and the potential impacts of channel deepening. We selected two tidal creeks which flow through salt marshes and tidal flats of the Cádiz Bay (SW Spain) in a singular network due to their double connection to the Atlantic Ocean and the inner bay. We study the interactions between tidal waves that penetrate into the creeks from these two different bodies of water, analyzing the tidal asymmetry and the morphodynamic tendencies of the system. For the analysis, we set up a hydro-morphodynamic model specifically developed for areas with very shallow and complex channels. Results show that the tidal wave penetrates within the tidal network both from the inner Bay and the open ocean with different amplitudes, phases and flow velocities. There is also an asymmetric pattern for the tidal flows caused by the deformation of the dominant astronomical tidal constituents, M2 and M4, due to the non-linear interaction of tidal currents with the irregular creek geometry and bottom topography. Tidal asymmetry promotes the progressive infilling of the area where the tidal waves meet closing the connection between the open ocean and the inner bay, such an infilling trend being accelerated by human interventions.