The hydrodynamic module solves the two-dimensional depth-averaged Shallow Water Equations (SWE), also known as the 2D Saint Venant equations.

These equations assume the hypotheses of hydrostatic pressure distribution and uniform velocity over the water depth. The assumption of hydrostatic pressure is satisfied in rivers as well as in tidal currents in non-stratified estuaries. The hypothesis of uniform velocity distribution usually complies in rivers and estuaries, provided that there are no relevant stratification processes due to differences in salinity, temperature or wind.

Related publications

• Bladé, E., Cea, L., Corestein, G., Escolano, E., Puertas, J., Vázquez-Cendón, E., Dolz, J., Coll, A., 2014. Iber: herramienta de simulación numérica del flujo en ríos. Revista Internacional de Métodos Numéricos para Cálculo y Diseño en Ingeniería, Volume 30, Issue 1, 2014, Pages 1-10, ISSN 0213-1315, DOI: 10.1016/j.rimni.2012.07.004  

The hydrodynamic module of Iber  can consider the following processes:

• Unsteady subcritical and supercritical flow computation
• Generation of unsteady hydraulic jumps
• Bed friction computed with Manning's formula
• Unsteady flood fronts
• Turbulent stresses calculated with different turbulence models
• Bed evolution due to Sediment Transport
• Different open boundary conditions: hydrograph, tidal level, weir, stage-flow hydrograph
• Wall-type boundary condition: free slip, wall friction logarithmic law
• Internal conditions: bridge, weir, sluice gate, culvert...
• Dam breach formation
• Hydrological processess (rain, infiltration...)
• Free surface wind friction computed with van Dorn's formulation
• Tools to calculate the flood risk zones in accordance with the Regulations on Public Water Supply

Iber incorporates several depth-averaged Boussinesq-type turbulence models to calculate the turbulent shear stresses. The following depth-averaged turbulence models for shallow water flows are included (Cea et al., 2007):

• Constant turbulent viscosity
• Parabolic model
• Mixing-length model
• K-ε model of Rastogi and Rodi

The user must decide which turbulence model to use according to the characteristics of the flow.

The sediment transport module solves the 2D Exner equation in order to compute the bed elevation evolution due to sedimentation and erosion processes, accounting for both bed load and suspended load.

The current version of Iber works only with uniform or quasi-uniform sediment granulometries, in which the grain size is characterized by its median diameter. Following versions of the model will implement specific formulations for sediment mixtures with non-uniform granulometry.

Bed load

The main features of the bed load sediment transport module are the following:

• Critical Shields stress for initial sediment motion
• Bed load formulations
• Wong and Parker (correction of Meyer-Peter and Müller formula)
• van Rijn
• Engelund - Fredsoe
• User defined relation
• Engelund - Hansen
• Bed slope correction for bed load transport (magnitude and direction)
• Rock layer position for non-erodible condition

Suspended load

The suspended transport is calculated by solving the depth-averaged convection-diffusion equation for the sediment concentration, including a sedimentation / erosion term which models the exchange of sediment between the bed and suspended load. The main features of this module are the following:

• Turbulent diffusion
• Term of deposition / resuspension
• Equilibrium suspended concentration computed from the formulations
• van Rijn
• Smith -  McLean
• Ariathurai
• Calculation of sedimentation velocity with the formulation of Van Rijn

Iber includes a Water Quality module (IberWQ) which computes the spatial and temporal evolution of several species including:

• Escherichia Coli
• Dissolved Oxygen
• Carbonaceous Biochemical Oxygen Demand
• Organic Nitrogen
• Ammoniacal Nitrogen
• Nitrites/Nitrates Nitrogen
• Temperature
• Salinity

A 2D depth-averaged transport equation is solved for each species, including biochemical transformations to model their mutual interaction. Wave forcing and non-isotropic dispersion of pollutants due to wave action, which might be relevant processes in coastal areas, can be computed from an external wave field introduced as input data by the user.

Since the transport equations solved are 2D, they do not account for stratification processes nor for 3D flow effects and therefore, the water quality model is only applicable to far-field computations. The results deteriorate when applied to stratified flows in which the concentrations and velocity fields are not uniform over the water depth.

Related publications

• Cea, L., Bermudez, M., Puertas, J., Bladé, E., Corestein, G., Escolano, E., Conde, A., Bockelmann-Evans, B., Ahmadian, R., 2016. IberWQ: new simulation tool for 2D water quality modelling in rivers and shallow estuaries. Journal of Hydroinformatics 18, 816–830. DOI: 10.2166/hydro.2016.235  
• Anta Álvarez, J., Bermúdez, M., Cea, L., Suárez, J., Ures, P., & Puertas, J., 2015. Modelización de los impactos por DSU en el río Miño (Lugo). Ingeniería del agua, 19(2), 105-116. DOI: 10.4995/ia.2015.3648  

Iber includes some features which enable the computation of rainfall runoff transformation and therefore, make possible to use Iber as a distributed hydrological model based on the 2D shallow water equations.

These features include:

• Definition of rainfall fields from rain gauges or from raster files
• Definition of rainfall losses with different infiltration models, including Green-Ampt, Horton and constant infiltration
• A specific numerical scheme for hydrological applications (DHD scheme)
• Utilities to smooth bad conditioned Digital Terrain Models

The present version of Iber does not include a groundwater flow module and therefore, the base flow component is not consider in the model. This limits its applicability as an hydrological model to short and intense rainfall events in which the contribution of the base flow to the total discharge is less relevant than the surface flow contribution.

Related publications

• Cea, L., Bladé, E., 2015. A simple and efficient unstructured finite volume scheme for solving the shallow water equations in overland flow applications. Water Resources Research, 51, 5464-5486. DOI: 10.1002/2014WR016547