MOHID Land is the hydrology module within the three-dimensional MOHID Water Modelling System. MOHID is an integrated system for water flow, consisting of three main modules: Water for three-dimensional fluid dynamics, Land for hydrology and Soil for groundwater flow. The MOHID Land module is a watershed mathematical model — or hydrological transport model — designed to simulate the flow of water in a drainage basin and aquifer. The processes which are simulated include two-dimensional overland runoff, infiltration into the ground, one-dimensional drainage network flow through rivers and canals, as well as (saturated and unsaturated) porous medium transport. The interactions between the different processes (like water exchange between aquifer and river) are calculated dynamically by the model, using the hydraulic gradients. The different processes occurring in a basin are programmed in different modules. The user can choose which modules to activate, allowing simulation of the desired ones only.
Contents
MOHID Land was developed within the framework of three EU-funded projects: EcoRiver, TempQsim and ICReW for the simulation of water flow in watersheds with pathways for river and groundwater flow. The porous media module was developed in close collaboration with soil scientists from EAN-INIA (Portuguese National Agronomic Station). Recently the ESA financed Aquapath-Soil project to apply mohid land to support irrigation using Satellite LAI as input to the model, obtaining maps of Actual Evapotranspiration.
Main processes solved
Dynamical time step adaptation
MOHID Land uses an adaptive time-stepping method in its main hydrodynamic cycle. Within an iterative cycle, if the water volume — of reach or overland flow or porous media — varies more than a user defined percentage during two consecutive time steps, the model automatically decreases the time step. Thereafter the model 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 within the module "Drainage Network" the time step may be reduced to very short intervals during flush events. This procedure avoids the occurrence of negative volumes and optimizes the time it takes to make a certain simulation, without compromising model stability. Time steps of the processes — computed in the different sub-models — can be chosen differently, adding more to the optimization of the computational cost.
GIS Model Interfaces
You can download interfaces to prepare inputs and to analyse model results. Presently available two options:
Source code
The latest source code of the model can be downloaded from Codeplex (Mohid Land in CodePlex). Just click on the download link, no need to register. For advanced users you can download the entire solution ready to compile.
Other users can just browse around the code of each module to check out equations. In the links below you can go directly to the version from 4 Feb 2011 and see code in html: