Three years ago these news : ‘NIWA partners with DHI as demand for modelling services increases’ was announced. The news covered a new research partnership between National Institute of Water and Atmospheric Research (NIWA), New Zealand and DHI Water & Environment. This partnership gave NIWA access to a wider range of reliable and internationally recognised computer models, including DHI’s coastal and ocean modelling packages, MIKE 3 and MIKE 21.
Recently Dr Alastair Senior from NIWA visited DHI and on that occasion he gave an interview. Dr Alastair is a coastal scientist and group manager for NIWA’s coastal modelling team in Hamilton, New Zealand. He has been with NIWA for 6 years. Besides a PhD in river and hydraulic modelling he also has a certificate for piloting microlight aircraft.
The photos below and left of the Raglan Estuary demonstrate one of the advantages of having such a certificate – to immortalise the views from the sky.
Approximately half of the modelling work carried out by Dr Alastair’s group is related to research studies, the other half are commercial projects. This ratio is about the same for NIWA as a whole. Many of the commercially oriented projects are EIA studies (see box) which require Resource Consents.
In connection with the application for permission to use or develop a natural or physical resource and/or carry out an activity that affects the environment (for example the construction of coastal structures), NIWA assists the client with conducting and preparing the Assessment of Environmental Effects (AEE) as required in the Resource Management Act of 1991.
"MIKE 21
has typically been applied in these studies, partly because a 2D approach often is sufficient, and partly because of the benefits of computational efficiency, theory and cell size flexibility." When asked about potential difficulties in modelling, Alastair says: “Sometimes the calibration can be a challenge in getting the tidal phase correct and including non-tidal forcings, as many of the locations are on open straight coasts, implying three open boundaries”. He continues: “The classic MIKE 3, which is the version that we presently possess, has a limitation in that flooding and drying is only allowed in the top layer. This makes simulating 3 dimensional processes in estuaries with extensive mud flats and a significant tidal range very difficult. However, one of the purposes of my visit is to set up the MIKE 3 Flow Model FM (Flexible Mesh) in a newly started research study of a tidal estuary”. The FM version does not carry this limitation, as the vertical resolution is depth- adaptive (sigma coordinates), which again can be distributed as equidistant or non-equidistant vertical layers.
The Raglan Estuary Study
Fine sediments are the topic of the research study in the Raglan Estuary approx. 40 km west of Hamilton. The estuary leads out to the rugged west coast of the North Island, which is famous for its left hand surf break at Manu Bay attracting surfers from all over the world. However, the purpose of the study is to model the transport of fine sediment from catchments through streams to the estuary. The tidal range of about 2½ m results in extensive mud flats. The catchments are forestry and open pastures as shown on the aerial photos. It’s a pure research project (no commercial bias) and cofunded by a local district council – Environment Waikato.
Says Dr Alastair: “The idea is to couple our catchment and in-house stream models with the MIKE 3 Flow Model FM of the estuary. We have a special agreement with DHI to use a development version of MIKE 3. I’m here to learn more about this model version, especially about ECO Lab, which we will use to code and compile our own mud transport equations”, and continues; “ECO Lab is great and can be used for much more than ecological applications, for example simulating the transport of sediments”. A PhD student is also working on a subproject looking at flocculation in the freshwater-estuarine interface.
“The study includes an extensive field experiment programme, and we hope to get a flood event in our records of sediment measurements in the combined river-estuary system. One issue is how to link models of different spatial and time scales (years, hours). When the integrated modelling is established it can be used as a management tool for the local county. Other research related issues, such as water quality, will also be piggy-backed on this project”.
“ArcGIS is extensively used in the project and it is a good development track to see that DHI gets still more GIS integrated in the models, like the Marine GIS tool and possibility to load layer files in the model setup editors. I would like to see this trend continue and increase, because clients really do like to see model data with something they recognised. For example, overlay of a proposed coastal development with aerial photos of existing surface utilisation and buildings”, says Alastair and continues: “Quality presentation is an important part of any commercial project. For example in relation to visualization of model results one of the advantages with the FM version is that results don’t look blocky”.
“The purpose of my visit to DHI is also to look at joint research projects. One of the subjects considered is the interaction between sediment and benthic communities. Hopefully this can work out and be a candidate for a coming news story here”. – Thank you.
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For more information about the DHI Software technology applied, please feel free to contact:
Erland Rasmussen ebr@dhi.dk