Reconnaissance Investigation of Sedimentation Patterns in a Small Modern Anthropogenically Influenced Inlet, Otūwhero Estuary, Abel Tasman National Park, New Zealand

Abstract

The structurally controlled Otūwhero estuary on the SE boundary of Abel Tasman National Park is a small partially filled incised valley. The small size, limited number of fluvial inputs, accessibility and surrounding land use made it an ideal candidate on which to investigate potential climate‐induced estuarine behaviour. Surficial sediment samples and short cores enabled recognition of 15 modern facies using a combination of field mapping of geomorphology, macroflora and macrofauna, observed sedimentary properties in the field, laboratory grain size analyses and the 2021 Google Earth image. This provided the basis for interpretation and mapping of facies using historical aerial photographs and satellite images for the years 1952, 1958, 1980 and 2001. The facies maps showed distinct changes over time in estuarine facies distributions, probably controlled mainly by changes in the fluvial system. Background sedimentation is augmented by storm events that caused sediment‐supplying landslides. Wave activity has generated a barrier spit at the estuary entrance that has changed significantly in size and morphology since 1952. Seaward of the barrier, bars have been continually present over the study period and more or less maintained their positions, although with some changes in orientation.