Engineers are set to begin working near the dam at Roath Lake in November to reduce the risk of flooding.
Arup will carry out ground investigations at the southern end of the lake, ahead of major works next year to upgrade the dam, which could include chopping down trees.
Cardiff council said the risk of the city being hit by extreme floods or heavy storms is growing due to climate change.
Recent modelling showed the spillway, that feeds out from the southern end of the lake, would be too small to withstand extreme flooding.
The council has applied for listed building consent, to get permission for the initial survey works to go ahead.
Councillor Michael Michael, cabinet member for clean streets, recycling and environment, said: “Climate change means we are likely to have more frequent and more intensive storms in Cardiff, so the dam spillway needs to be able to cope with the potential for these more extreme weather events.”
The works next year will likely mean chopping down some trees in the area to the left of the spillway looking downstream, near to the Scott Memorial Garden. The council said it would “seek to replace any trees that are felled”.
Roath Lake is a reservoir formed by the dam which runs along the promenade by the lighthouse. Parts of the park near the dam will be closed while the works take place.
Ground investigation works will take about a month in November. Then the construction phase is scheduled to run from November next year until late 2023.
Residents can find out more details from the council about the plans during an online webinar on October 12 at 6pm, or two drop-in events on the promenade at the southern end of the lake on October 23 from 9am to 2pm, and October 26 from 9.30am to 3.30pm.
Cllr Michael added: “Roath Park is one of Cardiff’s most loved parks, and a full public engagement programme is planned prior to works commencing, so that residents, businesses and park users are fully informed.
“The detailed study that will commence later this year and the improvements that will follow will ensure the future effectiveness of the dam, so the park can continue to be enjoyed safely as the impacts of climate change become increasingly obvious.”
Elsewhere in the city the council is also planning a huge £25 million coastal defence scheme along the mouth of the Rhymney River. Works are scheduled to run from February next year until October 2023.