Planning only way to solve tidal surge

to the Editor:

Recent interest in the prospect of dykeland flooding problems (“Storm surge could flood upper Bay of Fundy communities”, The Advertiser, Dec. 5, 2006; “Rising concern over sea levels”, The Chronicle-Herald, April 10, 2007, and the April 17 column by Glenn Ells, “Dykeland protection more vital than you think”) is cause for optimism.

Now that the issue has gained some recognition, perhaps planning will be initiated soon for a problem that has been slowly building long before global warming came along; the gradual rise of sea level relative to the Maritimes of about one foot per century. With global warming included, this rate may briefly increase to as much as three feet per century. But with good planning, laid well in advance, the problem will be entirely manageable.

As discussed briefly in my letter of Dec. 12, the solution is so old it is new, but, in reviewing this letter, I notice that I should fill in some context.

A continuous slow rise in maximum sea level, for a time, can be offset simply by raising the height of the dykes. But as sea level rises, relative to dykeland, this eventually will become impracticable.

The amount of material required to increase dyke height increases more rapidly than height does and cost of increasing height will become prohibitive. In addition, as sea level rises, aboiteau outlets are able to drain for shorter periods and breaching of a dyke by an exceptional storm surge would flood ever larger areas including, as Glenn warns, many roads that we take for granted.

The solution, in brief, is to work with the sea, not against it. As described by W. F. Ganong in 1903, the Acadians breached dykes when productivity started to decline and the sea brought in rich silt that, after a year or so of leaching to remove salt, restored soil fertility. But these new silt deposits have the additional effect of increasing dykeland elevation and this would eliminate the need to build higher dykes.

But also note that just breaching a dyke at intervals is not a good idea unless provision has been made for this procedure, so that infrastructure remains above water and only selected polders of dykeland are flooded at any one time.

And this is where long-range planning comes into play; the missing essential ingredient.

Yours truly

David H. Webster

Kentville