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.


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 Introduction screen of DrainCalc program
The hydrologic DrainCalc simulation program converts
rainfall into runoff (surface drainage) depending on
the characteristics of the watershed or catchment area.
The software uses a reservoir model with inflow
creating storage of water and outflow.
The model can also be applied to surface drainage.
rainfall-runoff simulation Example of DrainCalc application
The software model gives output graphics.
In this program there is an example of a fairly close
fit of the observed and simulated discharge (runoff)
of the stream in a small valley, as was calculated by
this program from the rainfall
simulated drain discharge Example of results of the DrainCalc model simulating drain discharge
The drainage system is to be characterised by a response function (or reaction factor)
alpha = A * runoff + B,
as can be seen using the option "Predict discharge or runoff from rainfall given the alpha function" in the input tabsheet. For the calculation of A and B from the characteristics of the system, a calculator is built in.

In this example the discharge of a subsurface drainage system is calculated for regular inputs of irrigation water using a reaction factor alpha=0.1 (A=0, B=0.1). For more details see the analysis article in section 4.2: Transient recharge-discharge relations