2022 CSDMS meeting-037

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Event Severity vs Frequency for a Patch of Seabed using Extreme Value Analysis (EVA)

Chris Jenkins, University of Colorado Boulder boulder Colorado, United States. jenkinsc0@gmail.com

An Extreme Value Analysis (EVA) model is realized for seafloor elevation changes in an area of shallow continental shelf in the North Sea. Extreme events have practical application in this area of abundant Unexploded Ordinance at the seabed and also wind energy projects. The events being examined are from the motion of seabed sediment in megaripples, sand waves, sand bars and sand sheets, but driven by normal and extreme swell- and wind-waves, tides and human activities. Changes of seabed elevation up to 8m in one year are observed, but rare.

The observational dataset for the study is a large, publicly available compilation of 3-decades of annual, hydrographic-standard bathymetric soundings in the German Bight, provided in gridded form at a spatial resolution of 50m. Counts of annual seabed elevation changes by elapsed time were compiled and related to the seabed features, such as tidal channels (which have previously been well studied).

The change statistics were compared to forms of the Generalized Extreme Value and Generalized Pareto distributions, per pixel and also by small morphodynamically uniform subareas. The Generalized Pareto distribution with coefficient c ≈ -6.0 to -6.5 appears to be the appropriate model, but adjusted according to water depths and locations on features.

The result suggests a method to statistically model seabed behavior including extreme events.