He says some of the rules will introduce extra costs to council and ratepayers because new consents will be required, and on-going monitoring costs.
The council doesn't now need consent for the discharge of stormwater but, under the draft plan, it would have to get consent from GWRC and meet certain conditions. He said the conditions were "overkill" for the area's size and there was a lack of evidence of harm to the environment.
"They should be vigorously opposed," he said.
"If they are adopted, they will impose extensive and, in my view, unreasonable requirements upon council that will cost the community dearly for little actual environmental gain."
Gravel extraction from water courses and the coast would be restricted, aimed at reducing erosion.
Mr Buchanan said the proposed limit was not enough for council's needs, which uses gravel for road construction, maintenance and flood control.
He said it was already a "mammoth process" to get consent and it would become harder under the plan.
Another rule was likely to make the consent process for wastewater discharges more difficult, adding time and costs to it.
Deputy mayor Viv Napier said GWRC chairwoman Fran Wilde previously told council there would be less bureaucracy.
"Farmers were [also] given the impression it was going to be easier."
Councillor Julie Riddell said many in the farming community were not really aware of the implications.
"There's a lot of people who have no idea of the effect on the day-to-day operations of their businesses."
Under the plan, farmers must prevent livestock from accessing waterways, wetlands and estuaries
There are also restrictions on water that can be used for farming activities, like irrigation and livestock drinking water.
Water meters must be fitted and usage recorded daily if the take is over five litres per second.
The council is to lodge a submission on the draft plan.
Public feedback closes on November 30.
GWRC will consider the feedback for the next version of the plan which is expected to open for formal submissions in mid-2015.