MohidLand hydrology model

=Overview=

MOHID Land is a executable of the MOHID Water Modelling System. Watershed mathematical model or Hydrological transport model designed to simulate Drainage basin and aquifer. In MOHID Land, different processes occurring in a basin are programmed in different modules, allowing simulation of the desired ones only. The processes simulated can be 2D overland flow, 1D drainage network transport, and 3D infiltration and saturated and unsaturated Porous medium transport. The interactions between the different processes (e.g. water exchange between aquifer and river) are calculated dynamically by the model, using hydraulic gradients.

MOHID Land was developed within three EU projects: EcoRiver [http://www.iambiente.pt/ecoriver/pt/projecto.html] , TempQsim [http://www.tempqsim.net] and ICReW [http://www.icrew.info] for the simulation of water flow in watersheds with pathways for river and groundwater flow. Porous media module was developed in close collaboration with soil scientists from EAN-INIA (Portuguese National Agronomic Station).

Main processes solved

*Drainage Network (Kinematic and Dynamic Wave equation);
*2D Overland Flow (Kinematic Wave equation);
*Infiltration calculated by Richards equation or Green-Ampt approach.
* Soil redistribution by Richards equation
* Aquifer flow by Darcy equation
*Evapotranspiration is calculated with the 'FAO crop reference evapotranspiration', a standardized Penman-Monteith equation. [http://www.fao.org/docrep/X0490E/x0490e00.htm#Contents]

Dynamic Time Step

MOHID Land has a dynamical time step in its main hydrodynamic cycle. Within an iterative cycle, if the water volume of reach or overland flow or porous media varies more then a user defined percentage during two consecutive time steps, the model automatically decreases the time step and recalculates the current solution with a smaller time step for the affected process (reach or overland flow or porous media). This process is repeated until the volume variation is less than the user defined value mentioned above. The time step dynamically increases again when the model verifies that flow is “stable”. For example Module Drainage Network time step may be reduced to very short intervals during flush events.This procedure avoids negative volumes and optimizes simulations time cost, without compromising model stability. Time steps of the processes computed in different sub-models, can be defined differently, adding more to the optimization of simulations computational cost.

References

* Ramiro Neves et al. (2008) Sustainable Use and Development of Watersheds [http://www.springerlink.com/content/t8178785515h7247/] . Retrieved October 2, 2008.