Study on the coastline evolution of eastern Po plain due to sea level change caused by climate variation and to natural and anthropic subsidence.
The entire study will be focused on the evaluation of the considered physical phenomena at three main scales: the global scale considers the global climate change affecting the study area, the macro scale, defined as the area around the Adriatic sea between the cities of Monfalcone and Cattolica (350 Km), and a local scale (of approximate dimension between 10 and 20 Km) which will mainly consider anthropic events.
Available data at the global scale will determine the Adriatic sea level rise at the macro scale. This will be used, together with the results of regional subsidence model, to assess a macro scale coastal dynamics. The results of this study will complement the local data for the simulation of the coastal evolution at the local scale. The effects of local subsidence due to fluid withdrawal, of sediment transport rates at river estuaries and of coastal man made structures on the coastline evolution will be assessed at three different sample sites, which will be selected on the basis of the prevalent importance of one of the phenomena over the other two (see figure 1).
The study will be subdivided into three distinct phases. The first phase (A) will deal with the identification and collection of the available environmental data related to the study. The second phase (B) will be concerned with the development and implementation of simulation tools for the prediction of the coastal dynamics as influenced by the combination of global sea level rise and subsidence. Finally the third phase (C) will cumulate the knowledge acquired in phases A and B and use it to develop forecasting scenarios describing the possible variations on the coastline.
The data will be divided into two main categories, MACRO and LOCAL, depending on their characteristics. The following scheme will be employed.
MACRO SCALE DATA (A1).
Sea level rise: data will be available from the results of several international and CE projects like Sea Level Rise Project UNEP, COST, MAST, EPOC, MEDSPA.
Sea hydrography: mean sea level data, moon tidal excursion, storm and "sesse" sea level fluctuations, partially available from "Servizio Idrografico della Marina Militare", "Servizio Idrografico e Mareografico Nazionale".
Bathymetries and beach profiles: current zero sea level contour line, bathymetric and beach profiles, both available from CNR and "Servizio Idrografico della Marina Militare".
Topography: D.E.M. (pixels of 200x200 m), soil usage maps, lithological and pedological maps, all obtained for satellite and aerophotographical data which are possibly available from the European Space Agency, Telespazio, Soyuz, ISPRA, "Ministero dell'Ambiente".
Geological features: composition of the layers and structural properties of the underground system from the upper Pliocene to the Quaternary, including average values for specific weight of the material, porosity, hydraulic conductivity, soil deposition rate. The data will be searched on relevant literature and from CNR, AGIP, Universities and "Servizio Geologico Nazionale".
LOCAL SCALE DATA (A2).
Climatology of the Northern Adriatic Sea: historical records of wind fields, available from "Aeronautica ".
Hydrodynamic data of the Northern Adriatic basin and the local sites under study: records of wave spectra, tidal excursion, currents, available from ENEL, AGIP, CNR and KNMI.
Historical data of the local sites: bathymetries, coastline evolution, deposition rates history of new or existing structures or constructions, storm records.
Sediment transport: grain size distribution data of river and coastal areas provided possibly as cross section distribution, sediment transport measurement in the rivers, sediment volume balance of the coast-river system; data are available from "Regione Emilia Romagna" and ARPA (formerly Idroser Agenzia).
Geological features: stratigraphic data, geotechnical parameters including compressibility and structural properties, natural gas reservoir geometry, hydrological parameters. The data will have to be referred to the first few hundred meters of depth for the most superficial aquifers and the first few thousand meters for natural gas reservoir. Data are available from "Regione Emilia Romagna", AGIP, Universities.
water and gas prediction: piezometric fields (from observation of approximately 100 existing well bores of the regional "Catasto Pozzi"), water and gas production data, available from "Regione Emilia Romagna" and AGIP.
The collected data will be analysed and homogenised and then put in a data base and connected with a G.I.S. system, which will form the base structure for the modelling package. The data analysis will focus also on the determination of general trends that may be possibly used in the simulation of the future scenarios. A flow chart of phase A is given in figure 2.
This phase will be dedicated to the development of the mathematical models and the study of their numerical and computational implementation. During this phase a pre- and post-processing system will also be developed to automatically link the different models with the G.I.S. and to perform spatial and temporal analysis of the data collected during phase A in order to prepare the input data for the simulations.
The description of the models is given below.
MODEL TO ANALYZE THE MACRO SCALE LITTORAL DYNAMICS (B1).
The model will be based on the G.I.S. It will combine G.C.M. data on the sea level rise with regional subsidence simulations for the evaluation of the position of the intersection line between the mean sea level and the coast.
The result will be obtained by comparison of the coastal D.E.M.s with the medium sea level through convenient use of the G.I.S. features.
REGIONAL SUBSIDENCE MODEL (B2)
Terzaghi's principle of effective intergranular stress will be used to simulate the compaction of the quaternary system subject to a time dependent deposition rate. Empirical relationships between porosity and permeability as function of depth will be employed.
A one dimensional model will be implemented to calculate the stresses along the vertical. Therefore only the vertical movement of the porous matrix and of water will be simulated
The model will be applied on the basis of the collected deposition data and will give prediction results to be used also in the coastal G.I.S. based analysis.
The following data will be used as input: time dependent deposition rate, porosity and permeability versus depth. The following data will be output: porosity versus time, effective stress and water pressure as function of time and depth, geologic subsidence trend.
SURFACE SUBSIDENCE MODEL (B3).
The mathematical model for the multiaquifer system will be made up by the coupling of the two dimensional flow equation in confined aquifers with the one dimensional vertical flow equation in the intervening aquitards, giving rise to an integrodifferential equation of flow; the subsidence will be modelled by the one dimensional consolidation equations, which will make use of the results of flow model.
Triangular finite elements will be used in the aquifer and will be coupled via convolution techniques with the flow in the aquitards. The calculated pressure variation will be used in a consolidation model to determine the final surface subsidence.
The numerical model will be implemented and calibrated on the basis of the hydrological parameters and consolidation properties of the selected study area as defined in the data collection phase.
The following data will be used as input: stratigraphy, hydrological parameters and consolidation properties of the multiaquifer system, water production. The following data will be output: piezometric levels versus time in the various aquifers, land subsidence.
DEEP SUBSIDENCE MODEL (B4).
The mathematical model of land subsidence due to gas removal is based on the theory of poroelasticity, under the assumption of isotropic medium, incompressible solid grains and of the validity of Terzaghi's principle. The layered porous system will be modelled by a half-space limited on top by a horizontal surface with zero normal and tangential stress.
The solution method will be based on the evaluation of a fundamental solution related to a unit pressure decline on a unit volume disk shaped reservoir by means of an axisymmetrical finite element model . The final subsidence will be obtained by superposition of the effects of effective pressure decline on the reservoir influence area.
The model implementation at the local scale will be based on the knowledge of the behaviour of compressibility vs. depth.
The following data will be used as input: natural gas reservoir geometry, compressibility and structural properties, gas production data. The following data will be output: reservoir compaction and land subsidence.
HYDRODYNAMIC MODEL (B5).
The hydrodynamics along the coastline of the study area will be analized using two uncoupled models that determine:
- the currents and water levels due to tides and storm surges;
- the wave climate.
The model is based on the vertically averaged equations of motion, the so called "shallow water" or "St-Venant" equations, and includes tidal forcing and the effect of storm surges. In this model short waves (due to storms) are not modelled.
The hydrodynamic model is a two-dimensional depth averaged numerical model: the solution is based on the finite difference method.
The Adriatic Sea will be modelled with a coarse grid model (macro model) to generate proper open boundary conditions for the high spatial resolution, fine grid local models of the three study sites.
The following data will be used as input: bathymetry of the Adriatic Sea, in particular a detailed bathymetry of the study area; data on tides in the Adriatic and meteo data for historical storms. The following data will be output: water levels and currents for tides and historical storms.
Wave Climate Model
The model estimates statistical properties of the wave energy at the desired locations along the coast using measured statistical information about waves, i.e. significant wave height and frequency composition and direction.
Depending on the wave measurement locations, the complexity of the bathymetry and the desired locations of wave output, interpolation methods and/or a ray tracking technique including refraction, shoaling and dissipation processes (bottom friction and breaking) will be used. The chosen technique will be supplemented and validated by applying a more complicated wave simulation model for a number of selected events. In a later phase the wave climate determination could be refined using a more sophisticated approach, where the hydrodynamic model is coupled to a model for wind generated waves.
The model will be applied on the local coastal sites.
The following data will be used as input: statistical wave data at selected locations; detailed bathymetry; meteo data for selected events. The mean annual wave climate (height, frequency and direction spectra) will be the output.
SEDIMENT TRANSPORT AND MORPHOLOGICAL MODEL (B6).
The model is based on the assumption that the dominating contribution to the overall sediment budget is the littoral drift. Further it is assumed that the littoral drift can be determined with an approach where the active part of the coastal profile can be considered quasi-uniform along the shore. The wave height and direction across the near shore zone are calculated considering refraction, shoaling and breaking. Combining the solution of the long shore and cross-shore momentum balance equations the cross-shore distribution of long shore current and setup are found. The sediment transport is calculated with a deterministic intra-wave period model, giving both the bed load and suspended load.
The long shore sediment transport for one specific set of conditions is found by a fully deterministic approach. The sediment budget is found by the use of the littoral drift model for the all wave components in the mean annual near shore wave statistics. On basis of the sediment budget the coastline evolution can be calculated, considering also the influence of structures and sediment contribution from rivers.
A morphological baseline for the existing situations will be carried out including a general morphological description of the coast and a calculated sediment budget for the present conditions. The sediment budget will be verified by the coastline evolution model in the restricted areas.
The following data will be used as input: local bathymetries; local sediment data; historical coastline evolution; local mean annual near shore wave climate; global subsidence and sea level rise; local subsidence data. The following data will be output: present annual sediment budget; estimation of the future coastline evolution.
Structure of the models package is given in figure 3.
The final phase will be devoted to the development of different plausible scenarios to be modelled by the simulation tools at both the MACRO and LOCAL scales.
MACRO SCALE SIMULATIONS (C1).
At the macro scale, through the simulation of different scenarios, it will be possible to determine the areas that may be most sensitive to the integrated effects of sea level rise and subsidence.
At least nine different scenarios will be obtained by the combination of the subsidence trend, as calculated by the regional model, with the minimum, average and maximum sea level rise at time frames 10, 50 and 100 years. The output results will consist of at least nine regional maps, which could be used to develop future land usage planning projects.
LOCAL SCALE SIMULATIONS (C2).
At the local scale the coast line evolution models will take into account the global sea level rise and the regional subsidence as already assessed condition. The main focus of the simulations will be on the effects of sediment transport, and therefore hydrodynamic characteristics, and anthropic subsidence. Return times of 10, 20, 50 and 100 years will be considered in all the simulation.
The different scenarios will be determined by considering variations of the most important factor at each chosen simulation site. The scenario characteristics will be finalized from outputs of the macro scale study, once the data analysis will be completed.
Results of simulations at the three local sites could be used as examples for the assessment of the environmental impacts that anthropic subsidence, in combination with climate changes and regional subsidence, can have on the local coastal dynamics.
Milestones will be included at the end of phases A, B and C (and of the project) and therefore after 10, 16 and 24 months from the commencement of the project.
3. ROLE OF PARTICIPANTS
The Department of Methods and Mathematical Models for the Scientific Applications of the University of Padova has the role of co-ordinator of this project: it will provide the key links between the partners of the study and the local Authorities. The department will be responsible for the collection of the available data on the subsidence; the set up of the subsidence models and the provisional simulation of the subsidence. ARPA will carry out the collection and critical analysis of available data and previous studies in the phase A setting up the G.I.S. database, create the pre- and post-processing system, prepare forecast scenarios and perform impact analysis on coastal environment at macro and local scale. The Hydraulics Laboratory of the Catholic University of Leuven will carry out the implementation of the hydrodynamic model, and will be responsible for the analysis of the local site application results. Danish Hydraulic Institute will carry out the implementation of the sediment transport and morphology model, and will be responsible for the analysis of the local scale application results. MED INGEGNERIA will be responsible for the general structure of the models package (data exchange, links between different models, etc.) and it will carry out the local site applications.
4. DELIVERABLES AND WORK PLANNING SCHEDULE
Phase A: technical description of the activities; G.I.S. database; index of referred bibliography and documents.
Phase B: technical reference of the models; pre- and post-processing system.
Phase C: technical description of the forecasting scenario simulations; contour maps of the most important results; summary of the methodologies employed and of the results for the information to the public and the local Authorities.
INTERDEPENDENCE BETWEEN TASKS.
Phase A1, A2 and the mathematical model implementations are independent.
Completion of the phase A1 is necessary to implement the B1 and B2 models on macro scale area.
Completion of the phase A2 is necessary to implement the B3, B4, B5, B6 models on the three local scale sites.
Completion of the phase C1 is necessary to give sea level rise data and regional subsidence data to the simulations of the phase C2.
5. COMPLEMENTARY PROJECTS
The most important complementary project is the EPOC project.
Title: "Climate change, sea level rise and associated impacts in Europe".
Participants: Coventry Polytechnic (co-ordinator, GB), Univ. of Athens (GR), NERC (GB), Univ. College Cork (IE), Univ. of Durham (GB), Univ. of East Anglia (GB), Geological Survey of the Netherlands (NL), Rijkswaterstaat (NL), C.N.R.S. (FR), Studio di Consulenza Ambientale (IT), Univ. Bremen (DE), Alfred-Wegener-Institut (DE), British Antarctic Survey (GB), The Geological Survey of Greenland (DK), Bundesanstalt fur Wasserbau (DE), Univ. de Lisboa (PT), Univ. d'Aix-Marseille (FR), B.R.G.M. (FR), Dienst der Kusthaven (BE), Univ. of Ulster (GB), Univ. of Utrecht (NL).
Interdependence with the project: the EPOC project aims to investigate past and future sea level changes and to assess the impact of such changes as a basis for identifying the environmental hazards involved for Europe. It will aim at: investigation of climate and sea level changes on a century time; the geological record and coastal processes; tides, surges and mean sea level; impacts of sea level change in Europe.