Sedimentation and regions freshwater influence in the Hauraki Gulf
Introduction
This report describes a sediment monitoring program over regions of freshwater influence in the Hauraki Gulf. Published 2018.Download the publication
Executive summary
A Region of Freshwater Influence (RoFI) is the coastal zone where there is a dynamically and ecologically significant quantity of lower salinity waters. A marine hydrodynamic model was run over such a domain around the Hauraki Gulf with 20 sources of fresh water, representing the 20 largest river flows in the model domain with the largest annual average sediment loads.
The modelling forms a pilot study designed to evaluate potential use of this approach for the addition of full sediment transport models. As such, the role of this work is to identify what is presently possible and areas for improvement.
The model has been validated by comparison of time-series of simulated temperature and salinity with measurements at the NIWA Firth of Thames mooring as well as for standard large-scale metrics like tides. Despite being a pilot study, the level of agreement is encouraging. Further model development around RoFI behaviour is in progress. This freshwater transport and dilution is a proxy for some aspects of sediment transport. Other aspects of sediment transport pathways remain to be validated.
With regard to sediment transport, the present work suggests future emphasis needs to be placed on wave resuspension, especially in regions like the very south of the Firth of Thames, in order to get reliable results. As a consequence, the primary initial focus here is on the transport phase of sediment and using “numerical tracers” to describe the transport of the freshwater that transports the sediment.