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.
Once again, it shows character in this dressing room. Once again, there's no quitting in here. We all wanted this so bad and we worked so hard to get home-ice advantage and we weren't going to let this one slide.
— Colorado Avalanche captain Gabriel Landeskog on his team's OT Game 1 win vs. Minnesota Wild