Financial terms of the deal, announced Tuesday, weren't revealed.
The 23-year-old Galiardi played only 35 games last season because of wrist and forearm injuries. He finished with seven goals and eight assists. The Avalanche selected Galiardi in the second round of the 2007 draft.
Rissmiller, 32, played for five teams last season, including the Lake Erie of the American Hockey League. He was originally signed by the San Jose Sharks in June 2003 and has played in 192 NHL games.
I definitely think going back down helped me, I had a lot of confidence down there, I played a lot of minutes and I think that helped me a lot. With the 37 games up here, that gave me experience as well. I know what it takes to play in the NHL and now it's time for me to show that I'm capable of being a full-time NHL player.
— Oilers forward Leon Draisaitl on finishing the 2014-15 season in juniors after playing 37 games with Edmonton to begin the season