RainOff :   a conceptual hydrologic rainfall-runoff (surface drainage) simulation model with a nonlinear reservoir
Totally free download of software

Summary:
The RainOff computer program, or simulation model, calculates runoff from rainfall on watersheds (hydrologic catchment areas) whose extension is limited by the condition that the rainfall can be assumed evenly distributed over the area. The program can be freely downloaded, it is free shareware in the public domain.
      The 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 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 rain into runoff (surface drainage) and flooding is produced.
      Modelling with RainOff gives the opportunity of predicting the hydrology of the watershed (catchmnent) and of flood forecasting as well as simulating discharge and water table height in subsurface drainage systems. For the latter case, the model program offers a calculator to compose the reservoir reaction factor or response function from the characteristics of the system.

Details:
The reaction (response) factor can be determined from recorded rainfall-runoff data. The program uses various reservoir functions and selects the optimal function. Alternatively, it is possible to introduce the reservoir function, together with rainfall data, and the program will calculate the runoff.
      On 12 December 2010 an extra graph was provided for the recorded rainfall-runoff statistics and trends, thanks to a suggestion by Mr. Juan Victoria.
      On 27 August 2012 the program was updated to include a quadratic reservoir function and on 1 december 2012 a Help function and an observed-calculated graph was added.
      More details are given in the program itself.

Start:
The program starts giving clicking on RainOff.Exe. More information is given in the program itself.

Documentation:
A description of the procedure and equations used in RainOff is found in this paper on the reservoir model.
              A lecture note ("Data Analysis") on drainage research with examples of RainOff applications is found on the articles page.
An example of the application of the Curve Number Method for the design of a surface drainage system for sugar cane plantations in a humid tropical coastal area can be found in a chapter ("Agricultural Drainage Criteria"), also on the articles page.

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

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introduction to rainfall-
           runoff software Introduction screen of RainOff program
The hydrologic RainOff 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 RainOff 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 RainOff 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