Techniques
The objectives will be pursued through a variety of techniques which will put together the three Research Units as concerns seawater intrusion and karst hydrogeology, whilst the UNI Bari Unit will focus also on the instability processes acting in rapidly evolving underground voids, and the formation of sinkholes. The entire project is subdivided into the following three milestones:
Milestone 1
Site-scale analysis
of saltwater intrusion
and sinkhole development
First, a detailed bibliographic research on seawater intrusion in karst areas, and on instability in underground environment, including the effects produced at the ground surface (i.e. sinkholes) will be carried out. During this phase all necessary bibliographical and cartographical material on the study areas, including geology, topographic maps and speleological publications (surveys, descriptions, photographs, etc.), will be recovered to enable the most proper organization of the field research. All this material will populate a database (Activity 1.1) to identify the different condition of seawater intrusion, the main features of sinkholes and caves in each setting, and their main characters of instability and evolution. The network of geographical data will be placed in a Geographic Information System, and a dedicated website will be created by the Research Unit of UNI Sannio (Activity 1.2). This website will be continuously updated to contain data of the project, for both scientific and dissemination purposes. During the first months, preliminary field trips will be organized to visit the selected areas, aimed at sharing in the field experiences and ideas between the three research units.
At the end of the third month a scientific meeting will be organized in Bari to define the actions and activities to be carried out in function of the specific peculiarities of the sites, and of the availability and interest of local authorities with whom to share the project outcomes. This meeting will be attended by all researchers involved, as well as by other researchers collaborating in the project. At the meeting, personnel from stakeholders and from regional offices involved in land management and planning (Autorità di Distretto dell’Appennino Meridionale, Servizio Regionale di Protezione Civile, ARPA, Acquedotto Pugliese) will be invited, too.
An international Steering Committee (SC) will be defined since the beginning of the project, in order to follow all activities, evaluate
the project design and actions, and provide suggestions useful to successfully develop the project. Members of the SC will be internationally known experts that will attend this (as well as the others) meetings in person or in remote, according to their needs. Furthermore, during the meeting the basis for the realization of the website of scientific and didactic spirit will be laid down. In this website all information about the project will be presented, also through instruments that can be useful from a didactic standpoint (lectures, videos, powerpoint presentations, virtual reconstructions, etc.). The website will initially contain all collected ancillary data, such as maps and bibliographical material on the study sites (Activity 1.3), but with the advancement of the investigations the site will be enriched with details and new data.
The main driving factors for sinkhole occurrence will be detected during Activity 1.4, through investigations with DTMs and detailed mapping of river terraces, flat surfaces and endorheic areas, characterization of local geology and geomorphology, and
geo-structural surveys (Activity 1.5). In particular, detailed surveys will be carried out using advanced laser scanning devices, integrated by drone flights for the outside environments, thanks to the instruments in dotation to the UNI Bari Unit. This activity will be aimed at searching for correlations between surface features, evidences of instability (subsidence, flooded areas, erosion, sinkholes), cave levels and underground morphologies. This will also contribute to reconstruct the evolution of the water table, and its relationship with the landscape evolution, both at the surface and underground. This part will be carried out with experts in DTM and GIS and geomorphological analysis of landscapes. Furthermore, also a photographic atlas of the sinkholes and cave morphologies and of the typical instability features in the caves will be included; in this atlas, particular importance will be given to documentation of some of the surface and submarine springs (Olarinoye et al. 2020), and to the precursory signs of likely failures in cave systems, such as extrusion wedges and bulging from the walls.
Milestone 2
Analysis of the
freshwater-saltwater
interaction processes
The processes of interaction between freshwater and saltwater will be the object of these phase of work. At this aim, geophysical surveys by means of different techniques will be designed and realized (Activity 2.1). The model parameterization will be tested by non-invasive geophysical measurements able to rapidly characterize flow processes in the bedrock at the field scale, and to highlight possible preferential path in the unsaturated zone (De Carlo et al. 2020, 2021). Particularly, time-lapse electrical and/or electromagnetic survey will be carried out to image the electrical conductivity distribution in order to monitor the water front dynamics.
At Palude del Capitano, and in other flooded sinkholes, sensors will be installed to monitor the water quality and to ascertain the presence of H2S-rich gases feeding the system from below (Activity 2.2). These actions will be carried out in collaboration with speleo-diver associations, active in Salento, and with whom the UNI Bari Research Unit is actively collaborating since many years. The direct monitoring in such complex underwater conditions, combined with outcomes from cave explorations in the surrounding areas, will significantly result in updating the knowledge on karst systems of Salento.
Aimed at characterizing the involved carbonate rocks (Activity 2.3), their physical properties will be investigated, and petrographic analyses will be performed at the geotechnical laboratory of Bari University, while hydraulic properties will be determined at the hydraulic characterization laboratory of CNR IRSA (Caputo and Nimmo 2005). In addition, hydro-geophysical measurements will provide information on the hydrological and hydraulic characteristics of the subsurface, as well as on the presence and motion of fluids in the unsaturated and root zone useful for model parametrization (De Carlo et al. 2021). The aim is to establish the relationship between corrosion or erosion rate, weathering resistance and pore geometry and typology. At the same laboratories, the climatic chamber will be used to analyze rock samples under temperature and humidity cycles, aimed to study the effects of accelerated environmental changes on the rock texture.
All the above analysis will result in the production of thematic maps (Activity 2.4), useful to depict the extent and variations in the freshwater-saltwater interface, the spatial distribution of sinkholes and of the most susceptible areas to future similar processes, and the development and features of cave systems, both subaerial and flooded.
During the activities of the second milestone, one meeting will be organized to discuss the preliminary results obtained and decide which detailed scientific researches should be carried out in the single investigated case studies. The report of the meeting will be included in the website, in the form of a collection of ppt presentations. In addition to the meeting, a series of seminars, open to the public (teaching and research personnel, PhD students, MSc students, grant holders), will be scheduled, during which the general and detailed aspects of seawater intrusion in karst, and the stability of natural underground voids, will be illustrated. The seminars will be particularly addressed to secondary school students, aimed at raising the awareness about geological hazards in karst coastal areas among the populations living in such environments. With the same goal, throughout the project other dissemination meetings with local communities and stakeholders to discuss about the issues of saltwater intrusion problems and geological hazards in karst coastal areas will be planned.
This milestone will cover most of the project life, lasting between 16 and 18 months.
Milestone 3
Assessment of the
coastal processes
in relation to Sea Level Rise
This milestone will be dedicated to interpretation of the data and the comprehension of the evolution of seawater intrusion through time, also taking into account the future predictions for sea level rise (a topic on which the UNI Bari Unit is working since several years). The genetic mechanisms that condition the development of failures in the different geological settings, and their evolution and progressive propagation, until producing surface effects in the landscape, with possible interaction with the society, will be examined too.
Once identified in the previous phases of work the present conditions of saltwater intrusion, and having evaluated the susceptibility to related phenomena such as sinkholes, this milestone will deal with building up possible future scenarios of sea level rise, and with ascertaining the related effects in terms of evolution of the interface, and impacts on society. In detail, the first activity (Activity 3.1) includes water analyses, both as regards the chemical and physical parameters, and isotopes as well. Water samples will be taken and analyzed to understand their genesis (shallow, or from deep-hypogenic sources), and the likely relationships between mineralization and geo-structural setting. The many years on going cooperation between UNI Bari Unit and local speleo-diving associations will allow to sample water also within the karst systems, in both the study areas.
In parallel, the reconstruction of the hydrological data series (Activity 3.2) and the analysis of recharge phenomena (Activity 3.3) will be carried out, with the goal to define a hydrological balance of the study areas, and to have available data to be used for the next step, that is implementing future scenarios of sea level rise (Activity 3.4).
The many effects deriving from climate changes and global warming, and from the resulting high rate of SLR, include, among the others, unprecedented over-exploitation of the groundwater resources, strong advancement of the interface between saltwater and freshwater, and development of associated coastal sinkholes and subsidence phenomena. To assess the expected effects of relative sea-level rise for the next decades, several sources of data will be considered (Scardino et al. 2022), starting from the sea-level-rise projections for different climatic scenarios (6th Assessment Report of the Intergovernmental Panel on Climate Change 2021). These data will be integrated with multi-temporal analysis regarding the coastal morphology and the variations in the shorelines, through the combined analysis of historical maps, aerial photographs, orthophotos and satellite images in order to model the future shoreline positions, and define the extent of the expected permanent flooding areas.
At the end of this work, maps regarding ingression of the interface between sea water and freshwater, the surface and subsurface effects of instability, and the related karst landforms, will be drawn up. These outcomes will be a very useful tool to plan Managed Aquifer Recharge (MAR) plants in the areas strongly affected by the salt water ingression to create such a barrier against the seawater intrusion and reduce its encroachment. These maps will also highlight the sites where the underground voids are close to the surface, that is where sinkholes might be more likely to be expected in the future, as the final effect of the upward stoping of underground failures. They will represent the basis for land use management and planning, and for civil protection issues as well. As regards the different actions dedicated to dissemination and exploitation of the project results (Activity 3.5), it is our intention to produce at least 5 papers in international journals. The papers will be published in the major international scientific journals (e.g.
Engineering Geology, Geomorphology, Hydrogeology Journal, Journal of Hydrology, Natural Hazards & Earth System Sciences, Natural Hazards, International Journal of Speleology, etc.), and will be presented at international and national congresses.
The results of all the researches will also be presented during the final Workshop, to be held at Bari, entitled “Climate change effects in coastal karst areas”. This Workshop will span over 4 days, with two days of scientific presentations, inviting the major world experts in the field of seawater intrusion in karst, underground stability and hypogenic speleogenesis, and two days of excursions.
The proceedings of this workshop, together with some papers on general issues, will be published in a special issue of an international journal, to be printed within one year from the end of the Project. As an additional, not less important, goal, a significant effort will be dedicated to transferring the new data on saltwater intrusion and water quality to managers of Apulia Region and Local Authorities, aimed at writing regional procedures and protocols to control the advancement of the saltwater intrusion process.
