Contact Energy Ltd confirmed it would extract about 50,000cu m of gravel as part of its resource consent conditions for the Roxburgh Dam.
Contact Energy head of hydro generation Boyd Brinsdon said excavation was to start from February to June, depending on flow levels in the Manuherikia River.
"If the flows remain relatively low as they are now, we’ll probably start fairly early in that window but if we have higher flows we’d have to wait until they receded."
The works would occur from the Shaky Bridge in Alexandra downstream to its junction with the Clutha and around the Galloway Bridge.
Mr Brindson said the energy company surveyed the bed of the Central Otago river "every two to three years or following a flood event of greater than 350cu m of water per second".
He said the work would ensure the build-up of sediment in Lake Roxburgh was not exacerbated.
"We’re trying to ensure the sediment for the Manuherikia River does not enter there.
"It’s mitigation of the effect on Lake Roxburgh."
A 45-tonne excavator digger had to be rescued at the river in Alexandra after it became stuck during sediment removal work in 2009.
