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CENAS Project

Technical Reports

Abstracts

1. Coastal evolution of the Upper Adriatic Sea due to sea level rise and natural and anthropic land subsidence (Un. Padova, ARPA, K.U.L., D.H.I., Med Ingegneria)
2. Prediction of mean sea level rise in the Upper Adriatic Sea (ARPA)
3. Collection and analysis of historical and hydro-geo-physical data at the sites of Ravenna, Cesenatico and Rimini (ARPA)
4. Numerical modeling of natural land subsidence over sedimentary basins undergoing large compaction (Un. Padova)
5. Numerical analysis of land subsidence due to natural compaction of the Upper Adriatic Sea basin (Un. Padova)
6. Simulation of land subsidence due to gas production at Ravenna coastline (Un. Padova)
7. Prediction of land subsidence due to groundwater withdrawal along the Emilia-Romagna coast (Med Ingegneria, Un. Padova)
8. Wave refraction in the Upper Adriatic Sea (K.U.L.)
9. Storm wave simulation in the Adriatic Sea (K.U.L.)
10. Storm surge simulation in the Adriatic Sea (K.U.L.)
11. Coastal morphodynamics in subsiding areas (D.H.I.)
12. Local morphological evolution of the coast in the Upper Adriatic Sea: Design and management strategies to control coastal erosion (Med Ingegneria, ARPA, D.H.I.)
13. Geographic Information System (GIS), Data Management System (DMS) and Data Visualization System (DVS) in the CENAS Project (Med Ingegneria, Un. Padova)
14. Flood risk analysis in the Upper Adriatic Sea due to storm surge, tide, waves, and natural and anthropic land subsidence (Med Ingegneria, Un. Padova)


1. Coastal evolution of the Upper Adriatic Sea due to sea level rise and natural and anthropic land subsidence
G. Gambolati, G. Giunta, M. Putti, P. Teatini, L. Tomasi
Dipartimento di Metodi e Modelli Matematici per le Scienze Applicate, University of Padova, Via Belzoni 7, 35131 Padova, Italy

I. Betti, M. Morelli
Agenzia Regionale per la Prevenzione e l'Ambiente dell'Emilia Romagna, Via Po 5, 40139 Bologna, Italy

J. Berlamont, K. De Backer, C. Decouttere, J. Monbaliu, C.S. Yu
Laboratory of Hydraulics, Catholic University of Leuven, De Croylaan 2, B-3001 Heverlee, Belgium

I. Brøker, E.D. Christensen, B. Elfrink
Danish Hydraulic Institute, Agern Allé 5, DK-2970 Hørsholm, Denmark

A. Dante, M. Gonella
Med Ingegneria, Via della Paglia 35, 44100 Ferrara, Italy

The Upper Adriatic basin has experienced in recent times continuous changes due to the precarious setting of the coastal environment and the low ground elevation above m.s.l. of many coastal areas. Major events which may influence the future stability of the beach profile include the natural and anthropic land subsidence, the sea level rise caused by the climate global change, storm surge and wave set-up, and the reduced littoral sediment transport. In the CENAS project all these events are addressed and simulated with the aid of ad hoc numerical models, and the modeling results are used to predict the Upper Adriatic Sea coastal dynamics in the next century. The models are integrated and implemented into a GIS together with a large database of all the essential information and records needed for the analysis. These data concern geometry, geology, hydraulics and meteorology of the basin, and the related input parameters. The area investigated by the project is 350 km long and comprises three local sites south of the Po river delta (Ravenna, Cesenatico and Rimini) where a detailed coastal study has been performed. The results indicate that a general regression of the beach is to be expected in the next decades, mainly in the area south of the Po river delta, due to mean sea level rise and land subsidence, and that a large portion of the present coastal lowland is potentially flooded in 2100 during severe meteo-marine events. The basin as well as the local risk maps of inundation have been built using the GIS and some indication is given as to the locations where major coastal defence actions are to be undertaken in the years to come.

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2. Prediction of mean sea level rise in the Upper Adriatic Sea
I. Betti, M. Morelli
Agenzia Regionale per la Prevenzione e l'Ambiente dell'Emilia Romagna, Via Po 5, 40139 Bologna, Italy

The state of the art of the sea level change has been analyzed considering long term change and short term fluctuation. The relative long term change has been considered as the sum of the eustatic change (caused by steric change in the volume of ocean water for thermal expansion, glacio-eustatic in the mass of ocean water, change in the volume of ocean basins and geoidal change) and the absolute land elevation change (caused by down-lift by regional and local subsidence, up- lift by tectonic movement and up-lift by unloading of continental shelves). Eustatic mean sea level in the past (during Quaternary, in the past 100 years) has been considered and mean sea level in the next 100 years has been estimated by the extrapolation from near past trend (1.2 mm/year) and forecasting models (3/4 times near past observed trend at 2100) and mainly considering the greenhouse effect as a forcing factor. The forecasting models of eustatic rise due to greenhouse effect (depending on socio economic models, gas emission models, gas cycle models, climate models and eustatic sea level rise models) have also been considered and combined with the scenarios of eustatic sea level rise. The proposed sea-level rise are those predicted from IPCC 92 scenario a according to which the mean value of the sea level change is about 50 cm within 2100. The sea level fluctuation has been considered on the basis of the following main causes: tides, seiches, wind waves and storm surges, where storm surges are the results of the combined effect of baric depression and induced winds.

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3. Collection and analysis of historical data on shoreline evolutin at the sites of Ravenna, Cesenatico and Rimini
M. Morelli
Agenzia Regionale per la Prevenzione e l'Ambiente dell'Emilia Romagna, Via Po 5, 40139 Bologna, Italy

The analyses of the three sites selected for simulation models on a local scale show the effects on the coastline caused by a rise in sea level due to eustatism, storm-surges, natural subsidence, and subsidence caused by anthropic activity. The cities present various problems regarding the morphological evolution of the coastline. These problems are linked firstly to natural factors and secondly to the influence of various human activities related both the use of territorial resources (extraction of fluids from the subsurface, excavation of inert materials from river-beds, stabilization of montane basins) and to the construction of major coastal works (port piers and interventions to fight erosion). The sites have been described by analysing the various structures which help to modify the coastal morphology, the evolution in time up to the most recent modifications, and also the current state of the beaches. The subjects are divided into two main themes (sea works and beach structure) rather than treat each site individually. The final scope of the work is to demonstrate how structural interventions along the coasts at the selected sites and the evolution of their sandy shores have proceeded at the same rate and have influenced one another.

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4. Numerical modeling of natural land subsidence over sedimentary basins undegoing large compaction
G. Gambolati, G. Giunta and P. Teatini
Dipartimento di Metodi e Modelli Matematici per le Scienze Applicate, University of Padova, Via Belzoni 7, 35131 Padova, Italy

The natural compaction driven by unsteady groundwater flow in an accreting isothermal sedimentary basin is investigated by a new numerical compaction model. We assume a process of continuous vertical sedimentation and make use of a 1-D model of flow where water flow obeys relative Darcy's law in a porous medium which undergoes a progressive compaction under the effect of an increasing load of the overburden. The time interval spanned by the simulation can be millions of years and soil porosity, permeability and compressibility may vary with the effective intergranular stress according to empirically based constitutive relationships. The model takes correctly into account the geometric non-linearity which arises from the consideration of large solid grain movement and is solved using both the Eulerian and the Lagrangian approach. It is shown that the Eulerian derivative of the total vertical stress is well approximated by the sediment loading rate, thus allowing for the removal of a heavy source of non-linearity in the governing equations with a significant acceleration of the iterative solution procedure. Preliminary results from the non linear model are compared with those of the linear model of Bredehoeft and Hanshaw [1968] which neglects the medium compaction. These results indicate that the geometric non-linearity is important in relatively compressible and permeable basins, i.e. in basins which display a significant deformation and are normally or almost normally consolidated.

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5. Numerical analysis of land subsidence due to natural compaction of the Upper Adriatic Sea basin
G. Gambolati and P. Teatini
Dipartimento di Metodi e Modelli Matematici per le Scienze Applicate, University of Padova, Via Belzoni 7, 35131 Padova, Italy

We have simulated the evolution of the accreting Quaternary column at three strategic locations (Venice, Po river delta, Ravenna) along the Upper Adriatic coastline. The analysis is performed by a 1-D nonlinear finite element model of soil compaction driven by groundwater flow in an isothermal sedimentary basin subject to a continuous vertical sedimentation process. The constitutive relationship of the most important parameter controlling the event, i.e. the soil compressibility vs the effective intergranular stress, has been derived from a number of oedometer tests carried out on samples taken from shallow and deep exploratory boreholes scattered through the study area. Dating of the sediments has allowed for the estimate of an average depositional rate at selected time intervals spanning the Middle-Upper Pleistocene, the Holocene and the historical times. The model has been run so as to reproduce the present day sediment thickness with a small excess hydrostatic pressure since the Adriatic Sea basin in known to be normally pressured. It is assumed that sedimentation in the last 0.5 My was substantially in equilibrium with subsidence so that the deposition surface remained at a constant elevation. The results of our analysis indicate a natural land settlement in the next century between 0.5 mm/y at Venice and 4-5 mm/y in the Po delta, with an intermediate value of 2-2.5 mm/y at Ravenna.

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6. Simulation of land subsidence due to gas production at Ravenna coastline
P. Teatini, G. Gambolati, L. Tomasi and M. Putti
Dipartimento di Metodi e Modelli Matematici per le Scienze Applicate, University of Padova, Via Belzoni 7, 35131 Padova, Italy

A large number of deep gas reservoirs are scattered both inland and offshore in the Upper Adriatic Sea sedimentary basin. Among these gas fields, the Angela Angelina reservoir is of major concern for the CENAS project because it is directly overlain by the shoreline extending from Lido Adriano to Lido di Dante in the Ravenna area. Angela Angelina is a very complex field consisting of 47 variously shaped pools located at a burial depth ranging between 3000 and 4000 m. The 31 largest pools will be depleted by 2014 with an ultimate pressure decline that is expected to exceed 300 kg/cm2 in some pools. A numerical study of the reservoir compaction and land settlement expected over Angela Angelina is performed by a new three-dimensional nonlinear finite element model. The constitutive relationship of the most important parameter controlling the event, i.e. the vertical soil compressibility vs the effective intergranular stress, is derived from a number of oedometric tests carried out on samples cored from deep boreholes scattered throughout the Upper Adriatic Sea basin. The results predict a final maximum land subsidence due to reservoir depletion equal to 20 cm over the gas field central area and a settlement of 12-14 cm on the coastal area directly overlying the reservoir. An approximate evaluation of the influence of the active waterdrive surrounding the gas field is also given. Field measurements of land subsidence occurred from 1977 to 1992 are shown to be sufficiently in agreement with the simulated results.

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7. Prediction of land subsidence due to groundwater withdrawal along the Emilia-Romagna coast
M. Gonella
Med Ingegneria, Via della Paglia 35, 44100 Ferrara, Italy

G. Gambolati, G. Giunta, M. Putti and P. Teatini
Dipartimento di Metodi e Modelli Matematici per le Scienze Applicate, University of Padova, Via Belzoni 7, 35131 Padova, Italy

After the Second World War the Romagna coastal stretch between the Po river delta and Cattolica has experienced a dramatic land settlement mainly due to the water withdrawal which has characterized the economic and tourist development of this area since the early 50's. A numerical study of land settlement due to water pumping from the Romagna regional aquifer system is performed by an uncoupled approach consisting of a three-dimensional hydrologic model based on the MIKE-SHE code and a one-dimensional consolidation model. The results of the hydrological model as been used as boundary conditions for the subsidence model, which is applied at some locations along the Romagna coastline where detailed stratigraphies are available. Both models are calibrated using the piezometric decline and land subsidence measurements from 1950 to present, and then applied to predict land settlement from 1995 to 2015 under two realistic water pumping programs. Numerical results provide during these 20 years an average yearly subsidence rate equal to 0.8 and 2.5 cm/year with the optimistic and pessimistic scenarios, respectively. An approximate evaluation of land subsidence from 2015 to 2100 is also given.

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8. Wave refraction in the Upper Adriatic Sea
C. Decouttere, K. De Backer, J. Monbaliu and J. Berlamont
Laboratory of Hydraulics, Catholic University of Leuven, De Croylaan 2, B-3001 Heverlee, Belgium

For the study of the morphological changes of the Northern Adriatic coastline, the information about the nearshore wave climate is needed. The backward ray tracing refraction model LOMBOK is applied on a high resolution bathymetry in order to compute the annual inshore wave climate at the local sites of Ravenna, Rimini and Cesenatico. Wave observations from offshore platforms are used as model input. The refraction model brings the offshore wave climate inshore to the ten meter depth contour line in front of the local sites. The model takes into account the effects of shoaling, depth refraction and dissipation due to bottom friction. The most important storm types in the Adriatic Sea are the Bora and the Scirocco. Depending on the storm type, a different directional distribution of the wave energy spectrum is assumed in the refraction model. The wave data from the offshore platforms are based on observations. These observations were done at two different platforms with a water depth of 26 and 50 m. The recording period for wave directions and wave periods differs considerably. A representative wave climate for the 30 m depth contour line was created from these measurements in order to find a suitable input for the refraction model. Because the directions are observed in classes of 30 degrees, the directional resolution of the model results is limited. The wave directions at the local sites, however, are a crucial input for the morphological simulations.

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9. Storm wave simulation in the Adriatic Sea
C. Decouttere, K. De Backer, J. Monbaliu and J. Berlamont
Laboratory of Hydraulics, Catholic University of Leuven, De Croylaan 2, B-3001 Heverlee, Belgium

When strong winds are blowing over a long fetch, high waves with a lot of energy are generated. In the Adriatic Sea, the Scirocco storms are marked by a steady south-easterly wind, which lasts for a few days. In the northern part of the sea, this results in powerful swell waves. They are very important for morphological effects during such a storm. The WAM wave model is used to hindcast the wave field during one of the historical Scirocco storms in the Adriatic Sea. At the local sites of Ravenna, Rimini and Cesenatico, the wave characteristics are determined. These are used for the morphological study during the storm. At several points in the Northern Adriatic Sea, the wave field is computed in order to estimate the wave set-up, which is needed to estimate the extreme high water elevation. The Scirocco storm is chosen from a set of selected historical storms. Using its pattern, the 1, 10 and 100 year storms are estimated. Each of these storms is simulated for the bathymetry at present and in the year 2050 and 2100. The bathymetry changes due to subsidence and sea level rise. The extreme water level at the local site of Ravenna is used to determine the return period of the storm.

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10. Storm surge simulation in the Adriatic Sea
C.S. Yu, C. Decouttere and J. Berlamont
Laboratory of Hydraulics, Catholic University of Leuven, De Croylaan 2, B-3001 Heverlee, Belgium

A storm surge prediction model has been constructed for simulating seven historical storms in the Adriatic Sea. The storm which could cause the highest surge levels at the Ravenna coast has been chosen as a reference storm for studying the combined effects on this area of various regional topographical changes, sea-level rises and future storm events. These future storm events have been generated by increasing the wind intensity of the chosen weather pattern. Storm surges have been simulated with the scenarios obtained from various combinations of the bathymetry changes and different wind intensities. Wind intensity has been found to have the most significant influence on the storm surge levels in the future. Topographic changes due to land subsidence and due to sea-level rise have very minor influences on the net surge residuals in the future. Due to the bathymetric nature of the Adriatic Sea, the surge residual can be slightly lower by increasing the water depth (e.g. due to sea-level rise) in the Northern Adriatic.

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11. Coastal morphodynamics in subsiding areas
B. Elfrink, E.D. Christensen and I. Brøker
Danish Hydraulic Institute, Agern Allé 5, DK-2970 Hørsholm, Denmark

The coastline evolution for 3 sites along the Northern Adriatic was simulated by numerical modeling of the sediment transport mechanisms. The effects of relative sea level changes and external sediment sources such as fluvial sediment input and nourishments are included in the analysis. Prior to the coastline evolution studies, a baseline study was performed where the different process parameters of the coastal sediment balance have been identified and quantified. The calibrated coastline evolution model was used to study the coastline development for different land subsidence scenarios which were supplied by other CENAS partners. The present work has shown that land subsidence is a main factor in the coastal sediment balance. Its importance is of the same order of magnitude as the littoral transport and the sediment input from rivers. The simulations of the coastline evolution have shown that the coastal erosion, which is observed at almost all investigated sites, can be reduced considerably, or even disappear completely if no subsidence occurred. The problems associated with subsidence are mainly of local character. The general pattern of coastal erosion in the region must be subscribed to the reduced sediment supply from the rivers. The establishment of schemes of detached offshore breakwaters has reduced the coastline retreat locally. However, in the lee side of these structures, the problems have become worse due to the lack of sediment supply from the littoral currents. This type of coastal protection will not lead to a sustainable coastal protection.

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12. Local morphological evolution of the coast in the Upper Adriatic Sea: Design and management strategies to control coastal erosion
B. Elfrink, E.D. Christensen
Danish Hydraulic Institute, Agern Allé 5, DK-2970 Hørsholm, Denmark

M. Gonella
Med Ingegneria, Via della Paglia 35, 44100 Ferrara, Italy

M. Morelli
Agenzia Regionale per la Prevenzione e l'Ambiente dell'Emilia Romagna, Via Po 5, 40139 Bologna, Italy

The subject of the present paper is the control strategy of the dynamic processes affecting the coastline on the basis of the results obtained from simulations conducted under the CENAS Project, regarding the morphological evolution of the coastline. The first part of the paper describes the local evolution around offshore breakwaters from a qualitative point of view. The accumulation rates related to waves, tides and longshore currents behind offshore structures are considered. Between the three selected local sites the protection scheme of offshore breakwaters has been used in the past mainly at Ravenna and along the northern side of Rimini. The physical processes related to these structures are described by DHI. The second section of the paper briefly reports the results of the simulations conducted at the three local sites, highlighting the evolutionary factors which play a major role in determining coastal stability and the results of the macro and local scale flood risk analysis. The last two parts list the various territory management strategies which may be adopted through medium-to-long-term planning or short-term actions for the purpose of limiting the subsidence caused by anthropic factors and of enhancing as far as possible river sediment transport, and deal with the planning criteria for safeguarding the shoreline and for harbor and coastal works in general.

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13. Geographic Information System (GIS) and Data Management and Retrieval System (DMRS) in the CENAS Project (Med-Ing)
A. Dante, M. Gonella
Med Ingegneria, Via della Paglia 35, 44100 Ferrara, Italy

P. Teatini and L. Tomasi
Dipartimento di Metodi e Modelli Matematici per le Scienze Applicate, University of Padova, Via Belzoni 7, 35131 Padova, Italy

The large quantity of non-homogeneous data resulting from the analysis of field measurements and the simulation of the different physical phenomena of CENAS have been organized in an `overall data management environment' developed in the course of the project. The structure of the environment is divided into two main modules: a Geographic Information System (GIS) and a Data Management and Retrieval System (DMRS). Manipulation of site-specific raster, vector, and point data has been performed by means of the GRASS package, a GIS system developed at the US Army Corp of Engineers. GRASS was used for the definition of digital elevation models of the study area and of the land use maps of the coastal regions of the Eastern Po plain, and for the analysis of littoral dynamics of the Upper Adriatic Sea coastline at the local and macro scales. The DMRS has been developed for the efficient storage and retrieval of the project data files. The files, in their original formats, have been organized in a subdirectory tree and subdivided into two main classes according to the related scale (macro or local). A further subdivision within each class has been establish according to the physical characteristics of the data and their possible utilization in the different simulation models that form the overall project (\em e.g. bathymetry, land use, subsidence). The capabilities of the World Wide Web (WWW) has been used for the implementation of a Data Retrieval System that easily allows the query of project data and at the same time the exchange of data between the different project partners. In the CENAS `WWW home page' all types of information about the project can be obtained, and field data and simulation results can be visualized or retrieved through Internet.

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14. Flood risk analysis in the Upper Adriatic Sea due to storm surge, tide, waves, and natural and anthropic land subsidence (Med Ingegneria, Un. Padova)
M. Gonella
Med Ingegneria, Via della Paglia 35, 44100 Ferrara, Italy

P. Teatini, L. Tomasi and G. Gambolati
Dipartimento di Metodi e Modelli Matematici per le Scienze Applicate, University of Padova, Via Belzoni 7, 35131 Padova, Italy

The low-lying coastal areas of the Eastern Po plain bordered by the Upper Adriatic Sea are characterized by environments (lagoons, marshes and river deltas) with a precarious hydrogeological features. In the years to come the setting of these zones will become more critical due to a relative sea level rise caused by global climate warming and natural and anthropic land subsidence, and increased mean sea level due to severe meteo-marine storms. The inundation risk related to these areas and the potential shoreline regression are analyzed in the next 100 years by a GIS procedure. The GIS known as GRASS is applied to account for the variations of both the ground and the sea level obtained from the model package developed in the CENAS project. The size of the flooded areas and the economic loss hazard associated with them are evaluated for the entire coastal profile with a coarser spatial resolution, and at Ravenna, Cesenatico, and Rimini with a more detailed resolution. Several situations are analyzed for different prediction times (at present, in 2050 and 2100), different storm return periods (1, 10 and 100 years), and two anthropic subsidence scenarios.

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Presentation author: Andrea Pellizzon