Stream 4B: Shore Protection

Moderator: Heidi Moritz, US Army Corps of Engineers, USA

Question – Hans Moritz, US Army Corps of Engineers: What considerations for breakwaters settlement on substrate have been incorporated and the obvious effects on the regional sea level change?

Answer – Brian Joyner: We talked about sea level change for the Norfolk Virginia project and how we would deal with that effect of the substrate. So it’s a very consistently sandy bottom. We’ve seen these breakwaters in place for decades, and we don’t see any settlement. So we didn’t take anything specific into account.

Answer – Dirk Heijboer: Same here!

Answer –Kevin Hanegan: This is something definitely glossed over in the presentation, but it’s a big consideration for projects in the region and I can address it. So we typically have soft substrates in these areas where high settlement is expected, anywhere between half a meter to a meter, sometimes more for what are relatively small rock structures. So we typically include a geotextile geocomposite kind of mattress that helps limit differential settlement. We of course over build. And I guess addressing sea level rise, we’re designing for the end of that design period taking into account both the settlement of the structures and the increase in sea level. These structures that we mentioned happened to be all constructed of stone, we were able to accommodate the level of predicted settlement with just a higher constructed height. We have another project also in Lake Pontchartrain with even worse soils that actually use some lightweight aggregate for the breakwater core, all with the goal of limiting settlement. And that’s something that’s a huge issue, especially in Louisiana and something that every project has to address.