Sedimentary processes operating around the entrance to a river mouth port, Westport, New Zealand Journal Paper
- Author
- Kirk, R.M; Hastie, W.J; Lumsden, J.L.
- Year
- 1987
- Journal / Source
- New Zealand Journal of Marine and Freshwater Research
- Volume
- 21
- Number
- 2
- Pages
- 337-347
- Keywords
- Westport; river mouth port; river mouth bars; sediment bypassing; tidal hydraulics; inlet stability; beach accretion; wave climate
- Summary
- The paper presents investigations of wave climate, tidal inlet hydraulics, and sand sediment bypassing at the entrance to Westport Harbour, South Island, New Zealand. The results complement and extend those of studies of bar morphologies and sediment characteristics already published. Longshore transport of about 1 × 10(6) m3/year is directed in a net eastward fashion across the inlet because of an in-built 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 across 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 of the predominance of bar bypassing. Contrary to the recommendations of several past studies, it is argued that improvements in navigation depths at Westport are more likely to be obtained through modification of the littoral drift system than they are from tidal compartment enlargement.