Francesco Gallerano

Management strategies for the control of eutrophication processes in Fogliano lagoon (Italy): a long-term analysis using a mathematical model

Abstract Models are developed and used to analyse and test different management strategies aimed at limiting eutrophication processes in Fogliano Lagoon: modification of lagoon hydrodynamics by tidal flow regulation, harvest of algae biomass, reclaim of sediments. Mathematical models, which have been constructed and proposed, simulate, on a multiyear time scale, the main ecological processes responsible for the most important effects of eutrophication: vegetal blooms, summer anoxia. For different management strategies, hydrodynamic fields produced by wind and tide, and three-dimensional concentration fields of significant species in the ecological phenomena, in water and into sediments, are quantified and compared. The species simulated are: in the water column dissolved oxygen, phytoplanktonic biomass, macrophytic biomass, orthophosphate, dissolved organic carbon, particulate organic carbon and hydrogen sulphide; in sediments dissolved oxygen, dissolved organic carbon, particulate organic carbon, orthophosphate, adsorbed phosphorous and hydrogen sulphide. On the basis of the results of the simulations carried out, the best management strategy limiting eutrophication processes in Fogliano lagoon has been pointed out.

A new representation of anoxic crises in hypertrophic lagoons

Abstract A new representation of the causes of anoxia in hypertrophic lagoons is proposed; field measurements show that, in high concentrations of organic matter and high temperature, anoxic crises may be correlated either with the anaerobic mineralization phenomena in the sediment layer or with the turbulent characteristics of the hydrodynamic field produced by external influence (wind, tide). Two different models have been developed which are able to simulate, respectively, the hydrodynamic field in the lagoon and the concentration fields of the biochemical species which are the most important in characterizing the phenomena, i.e., dissolved oxygen, organic carbon, and hydrogen sulphide. The results of the simulations are compared with field measurements to validate the representation of the phenomena. Furthermore the effect of forced recirculation by pumping, in avoiding anoxia in water, is quantified.

Response of Lake Piediluco to the change of hydrodynamic conditions and nutrient load reductions

Abstract In order to verify and quantify the efficacy of management strategies utilised to improve the water quality of Lake Piediluco in the long and short term, a model was developed to represent the unsteady and three-dimensional form of eutrophication processes and water anoxia phenomena. Such a model, taking into account the hydrodynamic mean and turbulent characteristic of the lake, allows the simulation of the spatial and temporal evolution of the concentration fields of the following species: (a) in water, dissolved oxygen, algal organic carbon, particulate organic carbon, dissolved organic carbon, orthophosphate, hydrogen sulphide; and (b) in sediments, dissolved oxygen, particulate organic carbon, dissolved organic carbon, orthophosphate, adsorbed phosphorus, hydrogen sulphide. This paper presents the simulation results using the following configurations characterised by: different hydraulic regimes of the lake; different external phosphorus loads introduced into the lake from discharges; different initial adsorbed phosphorus concentrations in sediments (obtainable by sediment reclaim) in certain critical areas of the lake. The simulations have detailed: (1) the characterisation of the lakes eutrophication behaviour in its present state and the vulnerability of the different areas of the lake to summer water anoxia; (2) the role of external and internal phosphorus loads on the eutrophication processes; and (3) the management options to improve the environmental conditions of the lake.

Three-dimensional numerical simulation of wind-driven flows in closed channels and basins

F. Cioffi, F. Gallerano And E. Napoli, Journal of Hydraulic Research 2005, 43(3), 290–301In the paper, a fully 3D finite-volume numerical model is developed and employed for the prediction of wind-induced flows in a regular channel and in a square basin with a complex bathymetry. Numerical results are compared with laboratory experiments.Numerical tests are then performed to investigate whether simplifying assumptions about the pressure distribution and the turbulente stresses representation can be employed in the simulation of wind-driven flows. The hydrostatic pressure assumption, resulting in the use of “quasi-3D” models, proved to be reasonably acceptable in order to obtain the vertical profile of the streamwise velocity component away from the boundaries. The quasi-3D model employed, nevertheless, provided incorrect velocity patterns near the upwind and downwind boundaries. The zero-equation turbulence model proposed by Tsanis [J. Hydraul. Div. ASCE 115 (1990) 1113] is also investigated by comparing the parabolic vertical profiles of the eddy viscosity coefficient assumed in this model w...

Compatibility of Reservoir Sediment Flushing and River Protection

In this paper, we propose a system of numerical models for the compatibility assessment of reservoir sediment flushing and protection of downstream river environments. The model system is made up of two simulation models. The first model simulates soil erosion in watershed slopes and sediment transport in the tributary of the reservoir by means of a weighted essentially nonoscillatory (WENO) method, which is conservative and fourth-order accurate in space and time. The second model simulates velocity and suspended solid concentration fields in the reservoirs. This model is based on the three-dimensional (3D) numerical integration of motion and concentration equations, expressed in contravariant form on a generalized boundary-conforming curvilinear coordinate system by using a conservative and higher-order accurate numerical scheme. The proposed system of models is applied to the Pieve di Cadore (Veneto, Italy) reservoir and to its catchment area. By comparing suspended solid concentrations that are discha...

Numerical simulation of wave transformation, breaking and runup by a contravariant fully non-linear Boussinesq equations model

In this paper we propose a new model based on a contravariant integral form of the fully non-linear Boussinesq equations (FNBE) in order to simulate wave transformation phenomena, wave breaking, runup and nearshore currents in computational domains representing the complex morphology of real coastal regions. The above-mentioned contravariant integral form, in which Christoffel symbols are absent, is characterized by the fact that the continuity equation does not include any dispersive term. The Boussinesq equation system is numerically solved by a hybrid finite volume-finite difference scheme. A high-order upwind weighted essentially non-oscillatory (WENO) finite volume scheme that involves an exact Riemann solver is implemented. The wave breaking is represented by discontinuities of the weak solution of the integral form of the non-linear shallow water equations (NSWE). On the basis of the shock-capturing high order WENO scheme a new procedure, for the computation of the structure of the solution of a Riemann problem associated with a wet/dry front, is proposed in order to simulate the run up hydrodynamics in swash zone. The capacity of the proposed model to correctly represent wave propagation, wave breaking, run up and wave induced currents is verified against test cases present in literature. The results obtained are compared with experimental measures, analytical solutions or alternative numerical solutions. The proposed model is applied to a real case regarding the simulation of wave fields and nearshore currents in the coastal region opposite San Mauro Cilento (Italy).

Modeling Bed Evolution Using Weakly Coupled Phase-Resolving Wave Model and Wave-Averaged Sediment Transport Model

In this paper, we propose a model for the simulation of the bed evolution dynamics in coastal regions characterized by articulated morphologies. An integral form of the fully nonlinear Boussinesq equations in contravariant formulation, in which Christoffel symbols are absent, is proposed in order to simulate hydrodynamic fields from deep water up to just seaward of the surf zones. Breaking wave propagation in the surf zone is simulated by integrating the nonlinear shallow water equations with a high-order shock-capturing scheme. The near-bed instantaneous flow velocity and the intra-wave hydrodynamic quantities are calculated by the momentum equation integrated over the turbulent boundary layer. The bed evolution dynamics is calculated starting from the contravariant formulation of the advection-diffusion equation for the suspended sediment concentration in which the advective sediment transport terms are formulated according to a quasi-three-dimensional approach, and taking into account the contribution given by the spatial variation of the bed load transport. The model is validated against several tests by comparing numerical results with experimental data. The ability of the proposed model to represent the sediment transport phenomena in a morphologically articulated coastal region is verified by numerically simulating the long-term bed evolution in the coastal region opposite Pescara harbor (in Italy) and comparing numerical results with the field data.

Analysis of the eutrophication trend in a deep lake

Abstract This paper presents a model for the analysis over many years of the eutrophication trend in a lake. The phenomenon is studied through analysis of the diffusion and transport of phosphorus and phytoplankton, considering the effects produced by the hydrodynamic fields. The mass balance equations for phosphorus and phytoplankton are solved simultaneously by means of a multi-layer finite differences model: since the exchanges between phosphorus and phytoplankton are related to production, decomposition and mineralization. This model takes into consideration the effects of physical parameters such as the vertical distribution of temperature, light intensity and water turbidity. The eutrophic trend in a lake may be studied with this model, as it allows for the simulation of the concentration fields of phosphorus and phytoplankton over many years without a heavy computational burden.

A new three-dimensional finite-volume non-hydrostatic shock-capturing model for free surface flow

In this paper a new finite-volume non-hydrostatic and shock-capturing three-dimensional model for the simulation of wave-structure interaction and hydrodynamic phenomena (wave refraction, diffraction, shoaling and breaking) is proposed. The model is based on an integral formulation of the Navier-Stokes equations which are solved on a time dependent coordinate system: a coordinate transformation maps the varying coordinates in the physical domain to a uniform transformed space. The equations of motion are discretized by means of a finite-volume shock-capturing numerical procedure based on high order WENO reconstructions. The solution procedure for the equations of motion uses a third order accurate Runge-Kutta (SSPRK) fractional-step method and applies a pressure corrector formulation in order to obtain a divergence-free velocity field at each stage. The proposed model is validated against several benchmark test cases.

Bottom changes in coastal areas with complex shorelines

ABSTRACT A model for the sea-bottom change simulations in coastal areas with complex shorelines is proposed. In deep and intermediate water depths, the hydrodynamic quantities are calculated by numerically integrating the contravariant Boussinesq equations, devoid of Christoffel symbols. In the surf zone, the propagation of the breaking waves is simulated by the nonlinear shallow water equations. The momentum equation is solved inside the turbulent boundary layer in order to calculate intra-wave hydrodynamic quantities. An integral formulation for the contravariant suspended sediment advection-diffusion equation is proposed and used for the sea-bottom dynamic simulations. The proposed model is applied to the real case study of Pescara harbor (in Italy).