Social Work Department staff ran the 24-hour service on-call, after their usual shifts, the report said.
"The call back duties often result in staff members needing to be 'stood down' to achieve the obligatory nine hour break period between shifts," it said.
The cost of the service almost doubled in the past year to more than $135,000, from about $73,000 the year before.
The numbers showed ED was over capacity more often in the past year to June, with 201 days where more than 50 people were waiting in ED, compared with 146 the year before. That was up from just 21 days over capacity four years ago.
"The current social work service delivery model is not sustainable," the report said.
It said a proposal for a formal rostered service in ED was being developed.
The report is set to be put to the CDHB Hospital Advisory Committee in October.
Committee chairman Andrew Dickerson said he could not say if extra support or funding would be given to the service. He said understanding the size of the problem was the first step.
The problems reflected continuing post-earthquake stress in the community, he said.
"This is consistent with what other places which have been through a major natural disaster have experienced," he said.
"It is a disturbing trend, and further evidence a business as usual approach is inappropriate and unhelpful."
Some of the cases social workers at ED have dealt with in the past year:
• Twins found on the side of the road in an upturned pram, with their mother nearby described as "not aware" and high on drugs
• A woman who threatened to slit her throat in front of her children
• A man who had a stroke, leaving no one to take care of his eight-year-old child
• A woman who had been locked in a room for more than 15 hours and repeatedly assaulted
• A woman who was dragged along a road behind a car her partner was driving
• A pregnant woman assaulted by her partner
• A dispute between a family in the Intensive Care Unit
• A badly burned man, who later died of his injuries
• Deaths of newborns and babies
By the numbers:
In the past 12 months at Christchurch Hospital there were:
• 97,874 patients at ED, up from 94,465 the year before
• 201 days where ED breached 'maximum occupancy', with more than 50 people waiting
• $135,368 spent on social work, up from $73,061 the year before.