Common risk-assessment framework for the North Sea

published at NSHC, Resurvey Working Group | 0
Paper for the 5th meeting of the NSHC Resurvey Working Group, Plymouth, UK, 18 September 2015

Steps towards a common risk assessment framework for the North Sea

Leendert Dorst, NL, 19 August 2015


In its meeting in Amsterdam in 2014, NSHC released Conclusion 112:

The activity within the DSS WG and the Re-survey WG has resulted in a greater

harmonization of survey strategies. Nevertheless the work is based on strategies for each

nation and the Commission recognized the need to verify the consistency of the strategies.

The Commission made the following decision:

The Re-survey WG to undertake a risk assessment analysis for the North Sea area, including the Dover Strait.


This conclusion reflects that:

(1) each MS has its own survey strategy, based on the physics of its part of the North Sea, the particularities of usage, and its own capacities;

(2) it is necessary to verify the consistency of the national strategies;

(3) we are expected to undertake an analysis for the entire NSHC region, in line with recent developments on risk assessment.


For each of those three parts of the conclusion, I have formulated some statements[1] to structure our discussion. The Resurvey Working Group is requested to consider each statement, in order to identify steps towards the realization of the conclusion.


(1) Statements on “one strategy per MS”

  • The morphology of the sea bed of each MS, and its dynamic behaviour, is fundamentally different.
  • There is considerable variety in the use characteristics of each MS’s sea area: shipping draught and intensity; presence of platforms and wind farms; sensitivity of the ecosystems; etc.
  • Each MS needs to make its own assessment of appropriate survey methods and the available capacity for each applied method, to find a  balance between risks and costs, taking into account strategic and political considerations.


(2) Statements on “verification of the consistency of national strategies”

  • The allocation of the available methods and capacity to specific sea areas should take the interests of all NSHC and BSHC MS into account.
  • Significant differences in survey efforts over boundaries should be avoided, through bilateral harmonisation of survey policies, unless the conditions at each side of the boundary are very different.
  • A transparent methodology for the allocation of survey resources is required, in order to give NSHC and BSHC MS an opportunity to ensure that its interests were taken into account by other MS.
  • An overview of the source data sets that are used for the national methodology should be visible to other HOs and all other stakeholders.
  • The resulting national strategy, either expressed as a series of fixed resurvey frequencies or not, should be visible to other HOs and all other stakeholders.


(3) Statements on “one analysis for the NSHC region”

  • A risk analysis for the entire North Sea would be valuable input to the national strategy, but could not replace a national strategy.
  • In spite of the physical and non-physical differences between MS noted above, a single risk assessment for the entire North sea is meaningful.
  • In spite of the physical and non-physical differences between IHO regions, it is useful to understand and follow risk assessment methodologies under development for other regions.
  • A risk assessment methodology for the North Sea should be specified after recent developments have been reviewed on a worldwide level; recent examples include those of LINZ, UNH, NOAA, and Dutch research consortia.

The Resurvey Working Group already made a simple start by making national resurvey strategies visible, as well as a combination of other relevant aspects (Action item 1). The “Interval” map is useful for those MS that work with fixed resurvey frequencies (BE, NL, DE). The combination map is difficult to understand and needs to be split into different themes.


A next step would be to create separate maps of a set of subjects, to allow each MS to make an overview of its source data visible. The subjects that I propose are:

  • depth
  • morphological characterisation, including an impression of expected dynamics
  • resurvey frequency (examples: map 1a and 1b)
  • applied S-44 order
  • date of last survey (example: map 2)
  • applied sensors (example: map 3)
  • shipping intensity (example: map 4)
  • maximum shipping draught (example: map 5)
  • administrative and usage areas[2] (example: map 6)

As another next step, I propose that each MS makes a short text available that describes its methodology to create a survey strategy, if available with a few references to explanations in more detail.


These two steps will provide insight and allow for subsequent verification of the national strategies. They should also lay a foundation for the application of a North sea wide risk assessment, when it is time to apply the worldwide developments to our region, and if the NSHC decides to continue in this way.


The new NSHC web site will provide a good platform for the visualisation of these subjects and descriptions, especially because work is in progress to show detailed depth values on that web site (the North Sea Bathymetric Database initiative).


[1] These statements do not necessarily reflect the Netherlands’ position.

[2] think of: boundaries; traffic separation schemes; planned and realized wind farms; deep water routes; PSSAs




Map 1a: combined NSHC resurvey policy (by Bernd Vahrenkamp (BSH) on behalf of NSHC Resurvey Working Group, 2014) Note the gap between BE and NL, and the overlap between NL and DE


map 1b

Map 1b: DRAFT NL survey plan with updated repeat frequencies (red: 2 years; orange: 4 years; yellow: 10 years; green: 15 years; blue: 25 years; grey:responsibility of Rijkswaterstaat)



Map 2: survey dates (red: 2015; orange: 2010-2014; yellow: 2005-2008; green: 2000-2004; blue: 1995-1999; purple: 1955-1994; grey: Rijkswaterstaat, or earlier than 1955)



Map 3: used sensors (green: MBES+SSS; yellow: SBES+object sonar; orange or red: SBES; light blue: foreign surveys or lead line)



Map 4: shipping intensity in 2009 (AIS based, taken from ValHYD project)



Map 5: max. shipping draught in 2009, including a 20% safety margin (AIS based, taken from ValHYD project)



Map 6: administrative and usage areas for the Dover Straight (status of 2011)


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