A Sediment Trend Analysis (STA®) in Support of Dredged Material Management in Lyttelton Harbour, Christchurch, New Zealand

Abstract

McLaren, P. and Teear, G., 2014. A sediment trend analysis (STA®) in support of dredged material management in Lyttelton Harbour, Christchurch, New Zealand. About 300 sediment samples were collected from outer Lyttelton Harbour for the purpose of carrying out a sediment trend analysis (STA). The purpose was to assess the sediment behaviour of dredged material placed along the harbour's north side, where disposal operations have been occurring yearly since 1969 (43 years ago at the time of sampling for the STA). Prior to 1969, material had been placed on the south side of the harbour. STA is a technique that determines net sediment transport pathways and the behaviour of bottom sediments from the relative changes in grain-size distributions. The STA determined 68 sample sequences (lines of samples) showing that the dominant source for the harbour sediments is from the steep surrounding hillsides. Sediments are moved from the shoreline into the harbour and progress seaward into the Pacific Ocean. There is no longer any evidence for dredged material on the south side; however, material on the north side becomes incorporated into the existing transport regime and can result in temporary deposition in its transport out of the harbour. The conceptual understanding of the transport regime and the dispersal of dredged material did not conflict substantively with previous hydrodynamic observations and modelling.