According to this link (which has been credible in the past):
“BURBANK, Calif. – March 15, 2012 – The mythology of the beloved animated franchise from Avatar: The Last Airbender creators, Michael Dante DiMartino and Bryan Konietzko, continues with the Nickelodeon premiere of The Legend of Korra on Saturday, April 14, at 11:00 AM (ET/PT), with a one-hour television event featuring back-to-back episodes.
“In the premiere episode, “Welcome to Republic City,” Korra leaves the safety of her home and travels to bustling Republic City to begin her airbending training. Once there, she is shocked to find a big city full of dangers, including criminal bending gangs and a vocal anti-bending revolution.
“In episode two, “A Leaf in the Wind,” Korra is living with her airbending teacher Tenzin on Air Temple Island. Frustrated with her inability to master airbending, she turns her attentions to Republic City’s famous Pro-bending Arena. There she befriends two brothers, Mako (David Faustino) and Bolin (P.J. Byrne), who compete in professional bending matches. Korra is immediately drawn to Pro-bending’s dynamic fighting style.
“Beginning April 1, fans may log on to nick.com for an interactive experience and introduction to Republic City. Show information, fun facts, micro games and additional new content make up this “Welcome to Republic City” online experience. Also leading up to the television series premiere, Xbox users will have the opportunity to download the first episode and trailer for free and purchase episodes from Avatar: The Last Airbender. The first The Legend of Korra episode will be available on VOD.”