MOHID Water Modelling System 


MOHID Land is a physically-based, spatially distributed, continuous, variable time step model for the water and property cycles in inland waters and main mediums and equations are presented in the image.

MOHID Land is an integrated model with four compartments or mediums (atmosphere, porous media, soil surface, and river network). Water moves through the mediums based on mass and momentum conservation equations. The atmosphere is not explicitly simulated but provides data necessary for imposing surface boundary conditions to the model (precipitation, solar radiation, wind, etc.) that may be space and time variant. The model is based on finite-volumes organized into a structured grid, rectangular in the horizontal plane, and Cartesian type in the vertical plane. Surface land is described by a 2D horizontal grid and the porous media is a 3D domain which includes the same horizontal grid as the surface complemented with a vertical grid with variable layer thickness. The river network is a 1D domain defined from the digital terrain model (DTM), with reaches linking surface cell centers. Fluxes are computed over the faces of the finite volumes and state variables are computed at the centre to assure conservation of transported properties. The model uses an explicit algorithm with a variable time step, that is maximum during dry season when fluxes are reduced and minimum when fluxes increase (e.g. during rain events).

Numerical Characteristics

Main Characteristics

Spatial DiscretisationFinite volumes
Horizontal GridOrthogonal
Vertical GridGeneric coordinates
Computation points distributionArakawa C
Time discretisation
  • Hydrodynamics - Explicit. St. Venant surface water friction term semi-implicit
  • Property transport – explicit or implicit

Main Processes

AtmosphereCan be forced with field data (monitoring stations) or meteorological models (HDF). Atmosphere properties can be interpolated spatially and temporally from station data
Porous Media
  • Hydrodynamics - 3D solving Richards equation
  • Property transport – Property transport and transformation (Biological and chemical reactions in soil as mineralization, nitrification, de-nitrification, immobilization, chemical equilibrium, property decay)
Surface Water
  • Hydrodynamics - 2D in run-off and 1D in river network solving complete St. Venant equations or kinematic wave and diffusion wave approximations
  • Property transport – Property transport and transformation in river as primary production, nutrient assimilation, property decay
InfiltrationSoil Conservation Service (SCS) Curve Number, Green Ampt equation and Richards equation
EvapotranspirationPenman Monteith and water availability in soil
Plant dynamicsPlant growth and agricultural practices (planting, harvest, kill, fertilization, pesticide application, etc.) including dormancy and SWAT crop database
ReservoirsDrainage Network and Reservoir interaction to account river flow impact due to man-made hydraulic infrastructures
Mediums InterfacePorous Media and Run-off interaction with Drainage Network is done using continuity equation (surface gradient between Run-off and Drainage Network, Richard's equation with level gradient between Porous Media and Drainage Network).
Time StepVariable time step adapted to fluxes magnitude and/or Courant number to assure stability in high fluxes and reduce simulation time during low fluxes