MOHID Land
Encyclopedia
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.
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 finaced Aquapath-Soil project to apply mohid land to support irrigation using Satellite LAI as input to the model, obtaining maps of Actual Evapotranspiration. Example of map obtained can be seen in Google Maps (see map).
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.
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:
Hydrology
Hydrology is the study of the movement, distribution, and quality of water on Earth and other planets, including the hydrologic cycle, water resources and environmental watershed sustainability...
module within the three-dimensional MOHID Water Modelling System
MOHID Water Modelling System
MOHID is short for Modelo Hidrodinâmico which is Hydrodynamic Model in Portuguese. MOHID Water Modelling System is a modular finite volumes water modelling system written in ANSI-Fortran95 using an Object-oriented programming philosophy, integrating diverse mathematical models and supporting...
. MOHID is an integrated system for water flow, consisting of three main modules: Water for three-dimensional fluid dynamics
Fluid dynamics
In physics, fluid dynamics is a sub-discipline of fluid mechanics that deals with fluid flow—the natural science of fluids in motion. It has several subdisciplines itself, including aerodynamics and hydrodynamics...
, Land for hydrology
Hydrology
Hydrology is the study of the movement, distribution, and quality of water on Earth and other planets, including the hydrologic cycle, water resources and environmental watershed sustainability...
and Soil for groundwater flow
Groundwater flow
Groundwater flow is defined as the "...part of streamflow that has infiltrated the ground, has entered the phreatic zone, and has been discharged into a stream channel, via springs or seepage water". In hydrogeology it is measured by the Groundwater flow equation.- See also :*Subsurface...
. The MOHID Land module is a watershed mathematical model
Mathematical model
A mathematical model is a description of a system using mathematical concepts and language. The process of developing a mathematical model is termed mathematical modeling. Mathematical models are used not only in the natural sciences and engineering disciplines A mathematical model is a...
— or hydrological transport model
Hydrological transport model
An hydrological transport model is a mathematical model used to simulate river or stream flow and calculate water quality parameters. These models generally came into use in the 1960s and 1970s when demand for numerical forecasting of water quality was driven by environmental legislation, and at...
— designed to simulate the flow of water in a drainage basin
Drainage basin
A drainage basin is an extent or an area of land where surface water from rain and melting snow or ice converges to a single point, usually the exit of the basin, where the waters join another waterbody, such as a river, lake, reservoir, estuary, wetland, sea, or ocean...
and aquifer
Aquifer
An aquifer is a wet underground layer of water-bearing permeable rock or unconsolidated materials from which groundwater can be usefully extracted using a water well. The study of water flow in aquifers and the characterization of aquifers is called hydrogeology...
. The processes which are simulated include two-dimensional overland runoff
Surface runoff
Surface runoff is the water flow that occurs when soil is infiltrated to full capacity and excess water from rain, meltwater, or other sources flows over the land. This is a major component of the water cycle. Runoff that occurs on surfaces before reaching a channel is also called a nonpoint source...
, infiltration
Infiltration (hydrology)
Infiltration is the process by which water on the ground surface enters the soil. Infiltration rate in soil science is a measure of the rate at which soil is able to absorb rainfall or irrigation. It is measured in inches per hour or millimeters per hour. The rate decreases as the soil becomes...
into the ground, one-dimensional drainage network
Drainage system (Geomorphology)
In geomorphology, a drainage system is the pattern formed by the streams, rivers, and lakes in a particular drainage basin. They are governed by the topography of the land, whether a particular region is dominated by hard or soft rocks, and the gradient of the land. Geomorphologists and...
flow through rivers and canals, as well as (saturated and unsaturated) porous medium
Porous medium
A porous medium is a material containing pores . The skeletal portion of the material is often called the "matrix" or "frame". The pores are typically filled with a fluid...
transport. The interactions between the different processes (like water exchange between aquifer and river) are calculated dynamically by the model, using the hydraulic gradients
Hydraulic head
Hydraulic head or piezometric head is a specific measurement of water pressure above a geodetic datum. It is usually measured as a water surface elevation, expressed in units of length, at the entrance of a piezometer...
. 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.
MOHID Land was developed within the framework of three EU
European Union
The European Union is an economic and political union of 27 independent member states which are located primarily in Europe. The EU traces its origins from the European Coal and Steel Community and the European Economic Community , formed by six countries in 1958...
-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 finaced Aquapath-Soil project to apply mohid land to support irrigation using Satellite LAI as input to the model, obtaining maps of Actual Evapotranspiration. Example of map obtained can be seen in Google Maps (see map).
Main processes solved
- Drainage networkDrainage system (Geomorphology)In geomorphology, a drainage system is the pattern formed by the streams, rivers, and lakes in a particular drainage basin. They are governed by the topography of the land, whether a particular region is dominated by hard or soft rocks, and the gradient of the land. Geomorphologists and...
(kinematic wave equation); - 2D overland flowSurface runoffSurface runoff is the water flow that occurs when soil is infiltrated to full capacity and excess water from rain, meltwater, or other sources flows over the land. This is a major component of the water cycle. Runoff that occurs on surfaces before reaching a channel is also called a nonpoint source...
(kinematic wave equation); - Infiltration calculated by Richards equationRichards equationThe Richards equation represents the movement of water in unsaturated soils, and was formulated by Lorenzo A. Richards in 1931 . It is a non-linear partial differential equation, which is often difficult to approximate since it does not have a closed-form analytical solution.Darcy's law was...
or Green–AmptInfiltration (hydrology)Infiltration is the process by which water on the ground surface enters the soil. Infiltration rate in soil science is a measure of the rate at which soil is able to absorb rainfall or irrigation. It is measured in inches per hour or millimeters per hour. The rate decreases as the soil becomes...
approach; - Soil redistributionWater retention curveWater retention curve is the relationship between the water content, θ, and the soil water potential, ψ. This curve is characteristic for different types of soil, and is also called the soil moisture characteristic....
by Richards equationRichards equationThe Richards equation represents the movement of water in unsaturated soils, and was formulated by Lorenzo A. Richards in 1931 . It is a non-linear partial differential equation, which is often difficult to approximate since it does not have a closed-form analytical solution.Darcy's law was...
; - Aquifer flow by Darcy's lawDarcy's lawDarcy's law is a phenomenologically derived constitutive equation that describes the flow of a fluid through a porous medium. The law was formulated by Henry Darcy based on the results of experiments on the flow of water through beds of sand...
; - EvapotranspirationEvapotranspirationEvapotranspiration is a term used to describe the sum of evaporation and plant transpiration from the Earth's land surface to atmosphere. Evaporation accounts for the movement of water to the air from sources such as the soil, canopy interception, and waterbodies...
is calculated with the 'FAO crop reference evapotranspiration', a standardized Penman–Monteith equation.
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:- a completely free interface from Mohid Website (www.mohid.com).
- a beta version of a new interface can be downloaded from Action Modulers.
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:
- Mohid Land Is the Main Program of Mohid Land
- Module Basin Is the top level of RunOff, Infiltration, River Flow and Vegetation
- Module Porous Media Simulates Water Flow in variable saturated soils
- Module Porous Media Properties Deals with all property transport in Porous Media.
- Module Sediment Quality Zero-dimensional model for primary production, nitrogen and carbon cycle in the Porous Media Soil and Aquifer)
- Module PhreeqC Zero-dimensional model for chemistry equilibrium of solution, pure phases, gas phase, solid phase, exchangers and surfaces in Porous Media (Soil and Aquifer)
- Module Run Off Module which calculates the Surface RunOff
- Module Run Off Properties Deals with all property transport in Runoff
- Module Vegetation Module to simulate plant development
- Module Drainage Network Module which simulates a 1D Drainage Network System
- Mohid River Network Program that allows to run river using SWAT-Mohid discharges
- Module CEQUALW2 U.S. Army Corps of Engineers zero-dimensional model for primary production that can be run to simulate water quality in the river
- Module Triangulation This is one of the modules for interpolation. This is useful to obtain distributed rain in space based on point time series.
- etc