The Garda Ombudsman has used footage from body cameras worn by gardai and social media clips to investigate 29 complaints related to water protests.
The watchdog said most of the cases alleged assault or excessive force and neglect of duty or abuse of authority.
Only one complaint resulted in a file being sent on to the Director of Public Prosecutions and no charges were brought, the ombudsman said.
It highlighted the cases in its annual report which also showed the oversight body heard almost 2,000 complaints in 2015 and 1,102 were deemed admissible.
The ombudsman’s office said that from September 2014 to August 2015 it took in the 40 complaints about the policing of anti-water charge protests and the installation of meters.
Some were inadmissible as they were anonymous or made by people who did not witness the incident but heard about it from others or saw it on the media.
The Garda Ombudsman said it appointed one officer to handle the investigations in case any recurring or potentially systemic issues were occurring.
It said the video footage was the principle source of evidence against gardai.
“No clear evidence of garda misconduct was shown in the majority of the videos and in some cases they showed that the actions of the gardai concerned were proportionate,” the report said.
The ombudsman’s office also said that more than one third of complainants did not co-operate with investigations or withdrew their complaints, making investigation difficult.
“T here was insufficient evidence in many of the other investigations to warrant criminal or disciplinary action,” the report said.
The ombudsman’s office also ordered a survey of public attitudes to its work at the end of 2015 which found only half of people are confident the watchdog can resolve a problem.
It found 83% agreed or strongly agreed that the Garda Ombudsman makes gardai more accountable for their actions
More worrying for the oversight body was figures that showed almost one fifth of people don’t know what they do and three in 10 people think the independent body is part of An Garda Siochana.
Chair of the Garda Ombudsman Judge Mary Ellen Ring said some reforms on possible disciplinary matters have been put to Government.
“We believe that some complaints, in particular those that relate to quality of service from gardai, are best addressed through a managerial rather than a disciplinary response,” she said.
“We would also like to see more engagement by gardai with the informal resolution process, when minor complaints are made.
“These types of complaints, as they are currently handled, are resource intensive for both Gsoc and the Garda Siochana – and often they do not provide a satisfactory experience for complainants either. Moving towards a resolution model must be a focus for Gsoc.”