More than 1.6 million will be spent on erosion control on beaches in Mercury Bay over the next couple of years.

Thames-Coromandel District Council has approved $991,440 out of its hazard management activity fund for extensions to rock walls at Buffalo Beach, in Whitianga, and at Cooks Beach.

Buffalo Beach Rd under clear threat from beach erosion.

This month $680,000 already approved for stage one of works at Brophys Beach also comes on stream.

Mayor Glenn Leach says the council has to act, but coastal erosion expert Jim Dahm says it's easy to over-react.

In a storm early last month, some sections of Buffalo Beach between the end of the latest extension to the original rock wall and the Buffalo Memorial Area eroded up to one metre and the road is now visibly under threat. Large areas of the beachfront at the Purangi Reserve at Cooks Beach have also disappeared. The Cook Memorial had to be removed and a number of pine trees were also lost.

'This June storm isn't a one-off and what's frightening is the rate that these areas of beach are disappearing. It's only going to get worse, so we need to do something about it,” Glenn says.

Jim says the eastern beaches of the Coromandel peninsula are in an erosion cycle but erosion at Buffalo Beach is being heightened by the end effect of the rock wall extension and before that by the end effect of the original wall.

However when roads or buildings are threatened, you can't argue with the need to act.

However at Cooks Beach, where that's not the case, it might be better to wait, he says. Significant erosion in the 1970s, for example, was followed by significant accretion of sand. The council could instead get consent for a wall but set a trigger point for action, such as when erosion gets closer to the road.

'Sea walls are very expensive and pretty ugly and very damaging to the beach in front of them,” says Jim. 'If you react too rashly, you're going to spend a lot of ratepayers' money on sea walls that may not be necessary.”

The council hasn't given any timeframe for the Cooks Beach extension which will continue the new landowners' wall just west of the reserve.

Work on the new Buffalo Beach 120m wall extension is planned to start late this year or early next year, subject to resource consent. The work should take two to three months. The council says the earlier extension which was finished late last year, stood up to the storm, protecting the road and reserve behind it.

Dune plantings further along the beach in the past 18 months have helped protect more than 200 metres and another planting of 100 -150m is scheduled for August-September. The plan is to have dune plantings along the rest of the beach up to the end of the rock wall. Regular sand push-ups will also continue.

Stage one of work at Brophys Beach will involve building a backstop seawall, made from geotextile bags, from the children's playground to the boat ramp. Subject to resource consent, construction is planned for early 2015. The wall, which will mostly be covered by sand, will replace rocks placed on the beach in emergency work several years ago.