ASR - A Global Partner for the Sustainable Management of Coastal and Marine Resources

Napier

Location: Napier, New Zealand

Type of Project: Numerical Modelling

Client: Napier City Council, New Zealand

ASR Projects- Napier

Aerial view of Westshore Beach and Ahuriri, showing the refraction pattern of waves moving into the bay. Inset: numerical model output of waves refracting past the Port of Napier.

Project Overview:

ASR Ltd investigated the coastal processes related to shoreline erosion at Westshore Beach in Napier. This included the collection and analysis of oceanographic field data and a numerical modelling study.

Project Outcomes:

Westshore Beach has been subject to erosion since the late 19th century due to a combination of human activities and natural events. In the past decade, the beach face above mean high water spring tides has been nourished annually to combat the continuing erosive trend. However, questions over the effectiveness and long-term sustainability of continuous nourishment have been raised.

ASR's study determined that the Port of Napier’s dredging and disposal methods were contributing to the problem by consistently removing sandy material from the littoral system and placing it offshore where it could not be naturally transported to the eroding shoreline. ASR Ltd recommended that the dredged material be placed further inshore (shoreward of the 5 m contour) so that it could be integrated into the naturally existing sediment recirculation route in the area. Furthermore ASR Ltd suggested that the dredge spoils be placed in a pattern that is at an angle to the beach in order to force a rotational effect on the incoming wave crests. This would act to reduce the magnitude of the erosive alongshore currents. The final recommendation was that the effect of the new disposal method be systematically monitored to assess any changes.

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