Overwash patterns – intial results from a little numerical model

I’ve been working today on a simplified model of storm overwash. According to my own sparse comments, I’d last tinkered with this code in December 2011. Not surprising, then, that it took all day to get reacquainted before I tore it down to the sills and started over.

Cumulative overwashing ('wet cells') during a simplified storm simulation.

Cumulative overwashing (‘wet cells’) during a simplified storm simulation. Hot colors correspond to frequent flooding during the model run; the hottest colors (highest frequencies) are nearest the breaches.

In this movie, there are four points on the left-hand side of the image at which a breach initiates – imagine a failure in a seawall or a levee, and water pouring through onto a flat back-beach expanse or neighboring floodplain. The white pixels track the various leading edges of the overwash as it finds flow routes across the model landscape. (The overwash moves across a surface stippled with random perturbations.) You can see the overwash fronts propagate, interact, and sometimes surge forward as new flood water piles onto water already ponded in the terrain’s lowest spots.

And if you keep track of the number of times each landscape grid-cell has gotten wet – essentially, a different way of recording the spatial patterns of these overwash events – then you get the image shown at right.

Seawall and expansive back-beach at St Ouen's Bay, Jersey (view north).

Seawall and expansive back-beach at St Ouen’s Bay, Jersey (view north).

There are lots of next steps from here, including coupling these overwash patterns to another simple model of seawall breaching. Later this month I’m headed to Jersey, in the Channel Islands, to see (among other things) their coastal defences during our annual field course with the second-year Marine Geography students. Last year, St Ouen’s Bay, on Jersey’s western flank, looked like the photo at left.

Stay tuned for the full story, coming in June, at this year’s Symposium on River, Coastal & Estuarine Morphodynamics (RCEM) in Santander, Spain…

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