Good Modelling Practice (GMP)

Jos van der Baan, a coastal engineer at Arcadis, says that Arcadis is a firm believer in GMP. “GMP gives our clients confidence and supports our internal training. It is part of our ISO quality management. The aim is to introduce modellers to GMP from the word go.” GMP is used to make deliberate modelling decisions, both objectively and subjectively. Objectively for reasons of sound underpinning and transparency, subjectively because the tools are in the hands of a person with expertise. The transition to online working due to COVID-19 and the transition to other support systems have certainly accelerated the relaunch of GMP at Arcadis.

Process steps and checks by colleagues

In modelling projects, Arcadis uses a step-by-step plan with a flowchart: from opening a modelling log to archiving. Colleagues conduct four interim checks during the process:

  • model set-up
  • scripts / tools
  • model results
  • model report

An experienced modeller implements those checks. There is a monthly modeller meeting and there is a ‘living document’, the Modelling Guidelines Report.

Auditor Arno Nolte is impressed by how the GMP system is organised. “The process steps, checks by colleagues and supporting technical resources are transparent and well coordinated.”

The second part of the audit involved the appraisal of a national and an international project.

Jubail Industrial City Waterfront Development

This international project in the Gulf region was conducted to determine the design water levels and the renewal of water in a canal. Delft3D Flexible Mesh Suite was used for this work because of the large variations in spatial detail in the model domain. A model that was already developed in 2014 was used as the basis.

Uncertainties relating to the model input and assumptions could not be reduced on the basis of measurements or in other ways, and so sensitivity analyses were conducted to visualise the effect of the uncertainties. Rufus Velhorst of Arcadis did the modelling work: “A modelling log was used to record the successive calculations and the variations. A colleague completed the model checks.

Arno Nolte suggested that it would be advisable to document the interaction in a more structured way where possible but he also had compliments for the modelling and the underlying structure.

arcadis herkwalificeert - al reggah district

Ems-Dollard Long-Term Field Measurement (MVED)

The national project is the long-term modelling for the Ems-Dollard. The combination of monitoring and models plays a major role here. The model focuses on flood risk management: the load on the primary flood defences generated by high water levels and waves. The model ranges from the North Sea to the waves on the dike. The aim is to test the measurements and to add to them if necessary. The desired or required accuracy of the model instruments has therefore not been established. The work was done with a model that was ‘frozen’ in 2018 for the purposes of comparison. An assessment will be made in 2022 to see whether adjustments to the model are needed. Klaas Lenstra of Arcadis is responsible for the modelling.

Arno Nolte thinks this project is very interesting because monitoring over a period of several years is combined with an approach with models. “It is also valuable that we are drawing on our knowledge of the Ems-Dollard system, an understanding of the processes and familiarity with the questions being studied. The approach to all this looks great.”

arcadis herkwalificeert - meerjarig veldmeting Eems Dollard


During the audit, the Arcadis modellers clearly demonstrated their experience and expertise in the field of Delft3D modelling. On that basis, the conclusion is that Arcadis qualifies for recertification.

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