Iarnród Éireann said it needs €230 million to fund a programme to protect major sections of the Dublin to Rosslare line from the effects of climate change.
The rail line runs for 168 kilometres and just under half of the route length (77kms) lies adjacent to coastal or estuarine environment, and is vulnerable to the impacts of climate change.
It said the project is to "secure the future of the line for generations to come".
The rail operator said the funding, which is to be spread over the coming seven years, would provide resilience of between 50-100 years.
The vulnerable areas are 60km from Merrion Gates to Wicklow 17km in the Wexford to Rosslare area.
Options such as breakwaters, beach nourishment, onshore revetment strengthening, and other interventions will be subject to detailed design in the first phase of the programme.
"Coastal railway construction and maintenance has always been a challenging environment, and throughout its history interventions have been required to protect the line from impacts on embankments, water coming over the line and coastal erosion," Iarnród Éireann said.
"However, the frequency and severity of impacts are increasing, with climate change causing more impacts in the last 20 years than in the previous 100 years," it said.
"As well as the effect on rail operations and requirement for remedial works, this has also caused losses of lands and habitats, including sections which are special areas of conservation," it added.
The East Coast Railway Infrastructure Protection Projects (ECRIPP) is funded by the National Transport Authority under the National Development Plan 2021-2030.
Jacobs Engineering has been contracted as multi-disciplinary consultants for the first phase of the programme which will deliver Detailed design and planning works, including environmental assessments and statutory submissions.
Works will be examined between Merrion and Dun Laoghaire, Dalkey Tunnel and Killiney Station, Bray Head and Greystones North Beach, Greystones South and Newcastle, Newcastle to Wicklow as well as at Bray North and Rosslare.
Iarnród Éireann corporate communications manager Barry Kenny said that the time for "sticking plaster measures" has passed.
"Historically, it's not something that is new to the railway, the area in Bray Head, as railway people would know has seen the line diverted three times in the early part of its existence, but it is just the intensity and the increase in frequency of these issues that require a major programme, rather than sticking plaster measures," he said.
Mr Kenny told Today with Claire Byrne: "We have had remedial works for many, many years to protect against the issues, but there is a need for a long-term plan, which is what this is."
He said that the option of moving the line entirely inland was explored and that would come with "an enormous bill".
"That section of line, the Dublin-Rosslare line, southside DART line, people who travel it will know just how scenic it is, that brings its challenges," Mr Kenny said
"Any railway construction along the coast does that, and for just under half of the full route length, it's either coastal or estuary type environment and is vulnerable to the impacts of climate change," he added.