Galiardi, 23, was limited to 35 games this past season due to two separate injuries. The Calgary, Alberta native finished with seven goals and eight assists for a total of 15 points.
Selected by Colorado in the second round (55th overall) of the 2007 Entry Draft, Galiardi has tallied 25 goals and 33 assists in 116 career NHL games. He recorded 15 goals and 24 assists in 70 games as a rookie in 2009-10, ranking him fifth among all NHL rookies in both goals and assists.
"We are glad to have T.J. under contract," Avalanche general manager Greg Sherman said. "We expect him to report to camp fully healthy and ready to go."
Rissmiller, 32, played for five different teams last season, which included two NHL clubs as well as Colorado's American Hockey League affiliate. He dressed in a total of 10 NHL games, one with Atlanta and nine with Florida to conclude the season.
The Belmont, Mass., native spent the majority of the year with the Avalanche's AHL team, the Lake Erie Monsters, where he tallied 11 goals and 19 assists in 43 games. He also spent time with the AHL's Rochester Americans and Chicago Wolves.
Originally signed by San Jose as a free agent on June 30, 2003, Rissmiller has appeared in 192 career NHL games, tallying 18 goals and 28 assists.