DrainCalc :   a conceptual hydrologic rainfall-discharge (subsurface drainage)-water table simulation model with a nonlinear reservoir
Totally free download of software


The DrainCalc computer program, or simulation model, calculates drain discharge from time-variable rainfall in subsurface drainage systems. Also it finds the fluctuation of the water table. It concerns a non-steady state (transient) situation. The program can be freely downloaded, it is free shareware in the public domain.
      The irrigation+rainfall is converted into recharge by routing through a retention reservoir from which water escapes depending on predetermined characteristcs as storage capacity, initial storage and maximum rate of escape (representing evaporation or natutal subsurface drainage). This first reservoir gives the recharge (rainfall excess) as overflow.
      The recharge is routed through a second, non-linear, reservoir with a reaction factor whose value depends on the storage level. Thus, the conversion (transformation) of irrigation+rain into drain discharge and flooding is produced.
      Modelling with DrainCalc gives the opportunity of predicting the hydrology of the drained agricultural land under varying irrigation, rainfall and evaporative conditions.
The model program offers a calculator to compose the reservoir reaction factor or response function from the characteristics of the drainage system.


The reaction (response) factor can be determined from recorded irrigation+rainfall-discharge or irrigation+rainfall-hydraulic head (level of the water table) data.
      The program uses various reservoir functions and selects the optimal function. Alternatively, it is possible to introduce the reservoir function, together with irrigation-rainfall data, and the program will calculate the discharge or the water level.
      More details are given in the program itself.


The program starts giving clicking on DrainCalc.Exe. More information is given in the program itself.


A description of the procedure and equations used in DrainCalc is found in this paper on the reservoir model.

A lecture note ("Data Analysis") on drainage research with examples of DrainCalc applications is found on the articles page.

An article "Influence of the soil depth on the functioning of a subsurface drainage system analyzed with the free DrainCalc model" can be read at: DrCalc.pdf

Further s similar article featuring the soil's drainable porosity instead of the soil depth can be consulted at pores.pdf


For improvement, I am interested to learn about your experiences with DrainCalc. For this there is a contact form.


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introduction to rainfall-
           runoff software
Screen print of DrainCalc program
The hydrologic DrainCalc simulation program converts
rainfall and irrigation into discharge depending on
the characteristics of the subsurface drainage system.
The drainage system is to be characterised by a
response function (or reaction factor)
Alpha = M * runoff + N,
For the calculation of M and N from the properties
of the system, a calculator is built in.

Alternatively, the Alpha function can also be determined
from a series of data on observed drain discharges
and/or levels of the water table.

Example of DrainCalc application
The software model gives output graphics. In this
example the hydraulic head in a drainage system in
an irrigated area is shown for different depths of
the impermeable layer (DIL).

simulated drain discharge
Example of simulation of drain discharge
In this example the discharge of a drainage system
in arainfed area is shown for different drainable
porosities of the soil (Pd).