Juan Antonio Bayona's The Impossible has been receiving high levels of praise from around the world since its late 2012 release. The Spanish production, starring Naomi Watts and Ewan McGregor, is the true story of a family vacationing in Thailand at the time of the Indian Ocean tsunami on December 26th, 2004. With a mix of practical, miniature and digital effects, the filmmakers strove to accurately depict the harrowing events of that day.

Watch the first wave sequence.

The first wave

The first visual effects challenge was to re-create the initial wave of destruction as it hits the resort the family are relaxing in. "The key idea always was to be realistic, to be very close to the 2004 tsunami in Thailand," says visual effects supervisor Felix Berges. "We had a lot visual references of the particular area of the real story and these were our references all the time."

Surrounding the area are pools, bungalows, palm trees, umbrellas and all sorts of other objects. To show the tsunami wreaking havoc on all of these structures, a combination of full scale, miniature and scaled water effects were employed.

1. Crafting miniatures

The bungalows and surrounding buildings were crafted at 1:3 scale by Magicon GmbH in Munich under supervision by Henrik Scheib. Only three and a half bungalows were built and then duplicated in compositing. The large scale miniatures were shot on an open air 80x100 meter water tank in Ciudad de la Luz, Alicante, Spain.

The model bungalows at 1:3 scale.
Resort setting at 1:3 scale.

2. Water dump

Before shooting in the Alicante tank, several tests were undertaken to design the look of the wave impact. This was done firstly in 1:50 scale in a setup created by Edinburgh Designs Limited. Then part of the 1:3 scale was built to see what the water's behavior would look like.

The 1:50 test setup by Edinburgh Designs Limited.
Testing part of the 1:3 scale model.

Ultimately, the final tank constructed was 25x12x4 meters and held more than a million liters of water. It consisted of a fast opening doors system that could generate a 1.5m high wave (4.5m in real scale). To surround the tank, Berges elected not to use a traditional greenscreen backing. "We wanted to have trees so greenscreen was not possible and we did not have enough budget to buy and light an additional bluesecreen. So I used a solution a little bit tricky, very cheap but very useful - we painted a metal structure that held the green fabric with sky blue. It was not a good bluescreen, we had to do more roto, but the composition was very easy and the integration was good."

Scale background plate.
Sky and background.
CG elements.
Final shot.

3. Final impact

The final resort inundation shots, featuring close and aerial views, were a combination of the 1:3 model, extra 1:3 water for extension work, a plate shot in Thailand and CG elements such as the trees and umbrellas. CG splashes created in RealFlow helped combine the plates. To give the water a specific dirt look, the filmmakers "used an ecological and safe tint and a lot of color grading, digital and shot debris," says Berges.

Thailand helicopter plate.
1:3 model with water.
Extra water plate to extend water.
CG palm trees.
Final shot.

In the flood

Subsequent scenes of the characters caught in the water surge also relied on a heavy practical approach to depict a kilometer long journey along the torrent. For this, a 15x60 meter channel complete with 35 water pumps was constructed. The pumps were able to move water around at the rate of 350 liters per second. "One important thing was always safety," notes Berges. "The actors were guided in a kind of 'pot' that was controlled to always be the correct speed - the speed of water plus a little bit more or less depending of the shot."

Original plate.
Final shot.

Extra plates of water were filmed in a clean channel with the appropriate light and correct perspective for each shot. Separate passes of debris deemed too dangerous to place near actors were also captured, and then the shots composited along with digital trees, water splashes and other set dressing elements.

The main company involved in the digital work was El Ranchito in Madrid, which Berges is part of. "We did all the wave, flood and devastation scenes," he says. "Fassman, a Barcelona-based company, was in charge mainly of the underwater nightmare and a lot of devastation shots, as well as removals." Click here for Fassman's VFX breakdown reel.

Bonus gallery and video
The water channel pumps.
Water plate for aerial shot of resort.
Final shot.

Actress Naomi Watts in the channel tank - original plate.
Final shot.

Original plate.
Final shot.

Watch b-roll of the miniature tank shoots.

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