Surf Science: Whangamata – What Makes Sand Bar (New Zealand)

The Whangamata Bar is regarded as one of New Zealand’s premier surfing waves. The steep faced left hander breaks along an ebb-tidal delta at the entrance to Whangamata Harbour.

The wave often produces long makeable barrels and high performance sections. The sand bar that sculpts these classic waves is at the centre of an ongoing debate. Claims that the wave quality has been degraded in recent years has directed frustration mostly towards a marina development in the harbour and associated dredging of the entrance channel. A new research programme hopes to determine what makes the bar what it is and why the waves are sick (and not the good sick).

Whangamata lies on the east coast of the Coromandel Peninsula, New Zealand. The focal point of the township is Whangamata Harbour, where the Moana Anu Anu Estuary meets other tributaries of the Whangamata estuarine system and flows out in to the Pacific Ocean. Estuaries are extremely dynamic environments, where a range of forces are acting at any one time to move and mould sediments. At Whangamata the resulting feature is an ebb tidal shoal, more commonly known as a sand bar. The persistence of this bar is achieved through equilibrium of the local forces, such as the tide and waves.

The waves at Whangamata are a big part of surf tourism on the Coromandel and the Whangamata Bar was included as one of 17 surfbreaks of national significance, protected under the New Zealand Coastal Policy Statement (2010). The surf breaks are an incredibly important resource, which is amplified by the ever expanding population of surfing participants. Unfortunately the socioeconomic pressures we apply to these natural features can result in the degradation or even loss of surfing waves.

Mundaka in Spain is a prime example of how a surfbreak dependant on an ebb tidal delta can be adversely impacted by human activity upstream and in many ways is comparable with Whangamata. The quality of the wave at Mundaka is world renowned, and was the site of ASP World Championship Tour contests from 1999 to 2004. However, after dredging of the Oka Estuary in 2004, the 2005 contest had to be cancelled because the all-important sand bar at the estuary entrance changed and the surfing conditions were deemed unacceptable for a professional contest. Luckily, dredging in the esturary was halted and the bar reformed, allowing quality waves to break again.

The marina at Whangamata was constructed in 2008 and necessitated the establishment of an access channel which is periodically dredged to maintain navigable water depths for boats using the marina. Initial studies suggested that effects on ‘The Bar’ would be negligible, however anecdotal evidence says otherwise, with local surfers reporting deteriorated wave quality following dredging activity and substandard surf since marina construction. The debate is ongoing and pressure is mounting to determine the facts.

In response, research will be conducted by Ed Atkin of eCoast Ltd as part of his PhD at the University of Waikato in New Zealand. The research is currently in its preliminary phase, but plans of a comprehensive fieldwork campaign, calibrated numerical models and surf quality monitoring will be integrated into the study. Outcomes of the research will be to determine the sensitivity of Whangamata Bar to natural process and anthropogenic (man made) effects. It is hoped that the results will aid in the sustainable management of Whangamata and other surf breaks worldwide.

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Source: surfrider, November 19, 2012