Coastal erosion management options for Pigeon Bay Recreation Reserve, Banks Peninsula

Abstract

Pigeon Bay Recreation Reserve is a small beach ridge system at the head of Pigeon Bay, Banks Peninsula. The reserve is 1.14 hectares near the head of the bay. It protrudes into the bay with a boulder beach, a spit and a sheltered sandy bay as its main coastal features.

The reserve is administered by the Pigeon Bay Recreation Reserve Board and is used for camping, fishing, tennis and barbecues. Since management of the area became the responsibility of the local residents in 1930, concern has been expressed for erosion occurring on the seaward face.

The reserve was found to have existed as a boulder bank in its natural state and to have been modified for ship building purposes in the 1850’s. The level of the reserve was subsequently raised considerably by material deposited on it by a slip from the hillside above and behind it.

Comparison of surveys carried out in 1929 and 1981 indicates that the seaward face of the reserve is retreating at 0.1 m yr⁻¹, that the spit is advancing at about 0.6 m yr⁻¹ and that the sand beach is advancing at about 0.6 m yr⁻¹. Average annual rates such as these disguise the fact that the changes tend to take place episodically, usually as a result of storm conditions. The reserve as a whole is increasing in area.

Movement of beach material, and hence changes in the shape and area of the reserve, is caused by littoral drift. The amount of material moved is not large and the movement is in a single direction, towards the bay head.

The board has three principal options to choose from. It may do nothing and accept the consequences of continued accretion and erosion. Alternatively the board may choose to build one of a number of structures to protect areas of the reserve subject to erosion. The third choice the board has is to feed the area of loss with appropriate beach material. These options are examined in detail and the likely consequences discussed.

The option selected by the board will reflect the long term management strategy that it adopts for Pigeon Bay Recreation Reserve.