"As soon as he confronted the offender, however, it would have become apparent to him that he risked assault and possible serious injury," his citation says.
"This outstandingly brave decision ultimately cost him his life."
Last year Brown was jailed for life with a minimum non-parole period of 16 years for Mr Hemmings' murder. His appeal was rejected by the Court of Appeal in March.
Mr Hemmings' wife, Jenny, and their children, Meghann, 22, Jessica, 19, and Gareth, 18, accepted the award on his behalf.
Mrs Hemmings said her husband made the ultimate sacrifice by helping someone in need.
The family would treasure his bravery award, she said.
Mr McLean and Anthony Mulder drowned after tying themselves to weaker swimmers in an attempt to get across a swollen river in the Mangatepopo Gorge in 2008.
John and Jeanette McLean accepted the award on behalf of their son, and were glad his actions had been recognised.
Anthony Mulder's parents were also at the ceremony to accept their son's award.
His father John Mulder said he was proud of his son, but it had brought back all the sadness.
Elim Christian College principal Roger Burton was awarded a member of the New Zealand Order of Merit for guiding the school through the aftermath of the tragedy, which claimed seven lives.
A New Zealand Bravery medal was also presented to Mark Taylor, Royal New Zealand Navy chief petty officer, who persisted in his efforts to rescue a HMNZS Canterbury crew member from the sea, and put his own life at risk on October 5, 2007.
Police dog handler Constable James (Zinny) Muir from the Bay of Plenty, and Constable Nicolas Corley from the Auckland suburb of Newmarket were also honoured today by Governor General Anand Satyanand.
Mr Muir was presented with the New Zealand Bravery Decoration for his effort in capturing a gunman who had fired at police in Mt Maunganui in June 2007.
Mr Muir also received a Gold Merit Award from the Police Commissioner and the Upham Award for bravery for his efforts.
Mr Corley received the New Zealand Bravery Medal for his actions in freeing a driver trapped in a burning car on August 23, 2008 in the Auckland suburb of Oranga. A car had crashed into a power pole, fences, and other vehicles and then burst into flames. Mr Corley was in a passing patrol car, when he stopped and ran to help the driver.
Acting police commissioner Viv Rickard said he particularly felt for the families of the posthumous New Zealand Bravery Star recipients.
"The courage of all these people, some of them very young, is inspirational as is the dignity, strength and compassion of their families," he said.
- NZPA