Environmental degradation of an estuary and management options: Whangape Harbour, West Coast, Northern New Zealand

Abstract

Whangape is a small estuary on the west coast of northern North Island, New Zealand with a broad Y-shaped harbour basin formed by the confluence of two mangrove-lined rivers – the Awaroa and Rotokakahi arms. For some time local communities (iwi) have been concerned over siltation, mangrove encroachment and diminishing traditional seafood resources (kai moana). Today’s mangrove forested inter-tidal flats, flanking lower and middle reaches of the river arms were largely in place by c. 6000 yrs BP. Enhanced siltation of the harbour basin from c. 700 yrs BP, followed arrival of Maori colonisers and accelerated through slope failure and erosion in the surrounding catchment brought on by deforestation accompanying Pakeha (European) settlement in the later 1800s.

There is a need to develop a catchment-wide management plan and a number of options have been identified. They range from doing nothing to various corrective measures including reforestation, revegetation of stream banks and stock control. However, because some of the problems arise at a distance from areas of impact, decisions will be fraught with difficulty.

Keywords

Whangape Harbour, siltation, hill-slope stability, mangrove advance, shell-fish habitat loss, management options.