Sedimentation in the New River Estuary, Southland (1981)
AuthorsThoms, Martin Charlesshow all
The New River Estuary is a large mesotidal estuary connected to Foveaux Strait by way of an inlet, and has two principle rivers (the Oreti and the Waihopai) flowing into it. The purposes of this study have been to describe the sediment distribution within the estuary; investigate the sediment source-sink relationships.; to calculate whether on a net basis sediment is being deposited in or eroded from the New River Estuary, and to investigate some of the influences on the sediment dynamics of this estuary. Textural analysis of the sediment indicated that there are three sedimentary environments within the estuary, and each is distinguishable due to the relative mix of fine sand. It was shown that Foveaux Strait is a dominant source of medium-fine sand. The Oreti River and the channels of the main estuary body are also important sources of these sediments. Medium-fine sand is transferred into the estuary and very fine sand is transferred out of the estuary and onto the continental shelf. Aerial photographs indicated that estuarine morphology was stable over a 31 year period (from 1947 to 1978). However a network of scour rods indicated that the intertidal sediment surface was spatially and temporally dynamic. It was calculated that on a net basis sediment was deposited in the estuary over a five month period. An important influence on the sedimentation of the New River Estuary has been the reduction of the tidal com partment by 25%, due to the reclamation of 12.2 km2.