New Zealand Journal of Marine and Freshwater Research abstracts

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Sedimentary processes operating around the entrance to a river mouth port, Westpoift, New Zealand

ROBERT M. KIRK¹

WAYNE J. HASTIE²

JOHN L. LUMSDEN²

¹Department of Geography University of Canterbury Private Bag, Christchurch New Zealand

²R. W. Morris and Associates Consulting Engineers Limited P. O. Box 8074, Christchurch New Zealand

Abstract The paper presents investigations of wave climate, tidal inlet hydraulics, and s^nd sediment bypassing at the entrance to Westriort Harbour, South Island, New Zealand. Thp results complement and extend those of studies of bar morphologies and sediment characteristics already published. Longshore transport oft about 1 X 10⁶ m³/year is directed in a net eastwjard fashion across the inlet because of an in-b^iilt misalignment of the harbour training walls. Approximately 90% of the drift is bypassed, and has been since 1921, by deflection and splitting of the main sediment streams through the inner and outer bars and a transverse channel aoross the entrance. The outer bar appears to be the submarine, downdrift extension of Carters Breach and river load appears to contribute an order of magnitude less sediment to the complex than annual littoral drift. River sediments and littoral drift are mixed off the harbour and a declining proportion over time is recirculated to cause progradation of North Beach. The tidal compartment contributes little to scour of the entrance because o f the predominance of bar bypassing. Contrary ;o the recommendations of several past studies, it is argued that improvements in navigation depths at West-port are more likely to be obtained through mod- ification of the littoral drift system thar from tidal compartment enlargement.

Keywords Westport; river mouth mouth bars; sediment bypassing; tidal inlet stability; beach accretion; wave climate they are river hydraulics; Received 8 April 1986; accepted 17 Septembe r 1986

New Zealand Journal of Marine and Freshwater Research, 1987, Vol. 21 0028-8330/87/2102-0337$2.50/0 © Crown copyright 1987 Received 8 April 1986; accepted 17 Septembe

PDF file of entire paper: medium quality (994K); (scanned from paper original: notes about this process)

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