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,
nonlinear, 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 rainfallrunoff 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.
More details are given in the program itself.
On 12 December 2010 an extra graph was provided
for the recorded rainfallrunoff 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
observedcalculated graph was added.
On 3 January 2018 the program was given more
versatility by dividing the runoff data into a
high and a low range with different reaction
factors.

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.
An article on rainfallrunoff relations of a
small valley in Sierre Leone using RainOff with a
nonlinear reservoir has appeared in the
International Journal of Environmental Science,
see this website
A comparison of results of the drainage software
EnDrain and RainOff for
steady and nonsteady state drainage flow and
water level can be consulted at
ResearchGate or on this
web site

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

Hints:
1  The model can also be used for hydrograph
analysis.
2  The model uses the periods without recharge to
detect the "signature" of the catchment. If in the
record such periods are missing, contact the
sitemaster. He can make available a version
(RainOffT) that detects the characteristics by
numerical optimization. Disadvantage: the
calculations need more time.
3  Also a version named RainOffQ can be obtained.
It does the same as RainOffT, but it uses a
quadratic function for the reaction factor instead
of linear. It uses still more time, but the
accuracy may be higher.


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RainOff
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RainOffT
