"But a common theme emerged around crossover of the role and function of the community restoration committee and the river and catchment management committee," he said.
"We've tried a different way of doing things this year, but it hasn't worked as well as we thought it might."
Rimmington said councillors wanted a structure that was cost-efficient and effective.
"This work accounts for around one-third of our core business and is vital to our economy and environmental prosperity. Bringing it under one umbrella will provide improved oversight and efficiencies," he said.
The new committee will be chaired by councillors Stuart Husband (north) and Stu Kneebone (south). Its membership comprises councillors Fred Lichtwark, Andrew MacPherson, Kathy White, Pamela Storey and Tipa Mahuta.
The terms of reference for the committee are due to be confirmed in the new year and will capture the work of both committees.