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24, chemin de Borde Rouge -Auzeville - CS52627 31326 Castanet Tolosan cedex - France

Last update: May 2021

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Soil Science Research Unit

Rainfall simulator

Simulator hall


General Description

The INRAE rainfall simulation hall is fitted out with rain generators in order to change the characteristics of the showers (duration, intensity, etc..), and the size of the experimental area (10 m² max.).

We are thus able to obtain a large range of experimental conditions in order to satisfy the needs of users. This equipment responds to the quality standard of INRA (traceability and reliability of measurements)

Rain generator

The rainfall simulator is composed with two rain generators with identical characteristics. The generators can be used simultaneously or independently.

Each generator consists of a boom of oscillating nozzles. This technique was designed in the 1980’s by the National Soil Erosion Research Laboratory (USDA-ARS, West Lafayette, Indiana). It permits to control almost independently the intensity of the rain, the drop size, while having excellent reproducibility.

A generator contains up to 5 nozzles. Depending on the experimental surface used, we can adapt the number of nozzles.

The size and the kinetic energy of the drops are defined by the nozzle model installed and the water pressure.

The rain intensity is controlled by the frequency of the nozzles oscillations: for each oscillation, a flash of rain is created. In multiplying by two the frequency oscillation, the rain intensity is doubling.


At the top, the 2 rain generators


Rain generator detail (top view)

We distinguish one oscillating nozzle.

Simulated rainfalls characteristics

The simulated rainfalls characteristics are adapted to the specificities of each experiment.

A rainfall can last from several minutes to several hours. The intensity range extends from 5 to 100 mm.h-1.

We can obtain raindrops with a median diameter from 0.5 mm to 2 mm.

The water used is controlled chemically.

According to the needs, we can use rainwater (collected on the building roof), tap water or deionized water.

To check the characteristics of the rains, we use adding pluviometers (intensity of rain) and a spectropluviometer (drop size distribution, speed and kinetic energy distribution). The simulated rainfalls have a space variability of 10 % for the maximum surface of 10 m². It is lower for smaller surfaces. Temporal variability is very low, about 1 %. The generated drops have a speed very close to their final speed.


Experimental devices

Your experiments can be carried out on your own devices.

Alternatively, we can use the existing devices or manufactured devices adapted to your needs. In particular, we have 2 boxes of 10 m² (divisible in 2 parts) and 3 boxes of 0.25 m². Designed to study the runoff and the soil percolation, they have a permeable bottom, an outlet to collect the runoff and an adjustable slope.


10 m² box

(c) INRA

0.25 m² box

Experimental measurements

The laboratory has a wide range of measuring instruments to collect your experimental data.

These measurements can be performed in real time (followed tensiometric, runoff flows) or delayed (sample collection). It can be physical measurements (rugosimetry, partical size), chemical (pH, ions, gas) or mineralogical (X-ray diffraction).