Under Salt Marsh’s production designer explains how to flood a set
Here’s how the show’s town was built in a giant water tank.
In Sky Atlantic’s Under Salt Marsh, which is set in the fictional Welsh town of Morfa Halen, an impending, catastrophic storm threatens to upend an investigation into a shocking crime.
Former detective-turned-teacher Jackie Ellis (Kelly Reilly, Yellowstone) discovers the body of her eight-year-old student, Cefin, who appears to have been drowned. Ellis’s former partner, Detective Eric Bull (Rafe Spall, Trying), is leading the investigation, but they fell out three years previously, when Ellis’s niece Nessa disappeared and Bull accused Ellis’s sister.
Time is of the essence to find out what happened to Cefin, with a storm that’s been brewing throughout the entire series threatening to wipe any potential evidence from the crime scene and cause general widespread chaos. While you can use pop-up water tanks, production designer Stevie Herbert and her team built their own unique tank for the huge, weighty build.
As she explained to Radio Times: "It’s quite nerve-wracking building a tank. It’s not an ordinary thing to do and it was very difficult. You obviously can't flood real towns in north Wales and control it and not damage"things, so we built an exterior set, a backlot, of Morfa Halen’s central hub of shops just outside Dragon Studios in Bridgend."
The tank was 50 x 50 metres and made of steel walls that were 1.2 metres tall. They used timber, glue and expanding foam to seal it, with tarmac wrapping a seal around the tank.
The flood scenes took a week to film. "Dragon Studios dealt with the license for the water, which turned up in these enormous bowsers that pumped water over the side with huge hoses," she says. "The water filled very slowly and shooting was scheduled around the different water levels – from 20 centimetres to almost a metre – and stunt sequences with vehicles and cast. It's a lot of weight. We had to do a bit of sandbagging and resealing.
"Rain rigs went above the whole set. In a flood, you get a current, so special effects created the current in the tank with pumps, so there were a lot of things moving around. We also had rooms that sunk down on hydraulic jacks, where the floor was made of metal mesh, so the water came through to flood it slowly."
Water is, of course, very difficult to work with, especially when it’s deep, as Herbert mentions that some items sink, while others become trip hazards. "I was dressing the set at different stages, so I had full waders on with my props team. You're working with dive teams.
"You can let some stuff float upside down, like plastic chairs, bowls and pots. We removed anything that was a problem or was going to explode. We stripped out units so there were no moving parts inside. We can cheat a lot with spray paint effects to look as if things are covered in mud."
The sets had to sit in water for a week, meaning there could be no toxicity in it. "Afterwards, the water is dispersed slowly back within the normal water system," Herbert explains. "The steels were clean, we used natural materials to build walls, which were all timber and ply-based, and the paint treatments had to be water-based."
In episode five of Under Salt Marsh, rising floods cut Morfa Halen off from the world and another body is discovered. As residents evacuate and attempt to get to safety, the killer still hasn’t been identified. Hopefully it’s not too late as the devastating storm hits at full force in the finale.
"It's not easy to imitate nature," says Herbert. "The storm and the flooding being believable was the biggest challenge. You've got to feel the fear, but you've also got to feel the potential loss of all these people."
The final episode of Under Salt Marsh will premiere on February 27 on Sky Atlantic and NOW at 9pm.
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Authors
Laura Rutkowski is a Commissioning Editor at Radio Times magazine, where she looks after the View From My Sofa slot, and the "What it's like to…" column, which spotlights behind-the-scenes roles within the TV and film industry. She loves finding out how productions are made and enjoys covering a wide variety of genres. Laura is half-American and half-British and joined Radio Times in 2022. She has a degree in Psychology and a Master's in Magazine Journalism.
