http://phys.org/news/2015-03-japan-opts-massive-costly-sea.html Four years after a towering tsunami ravaged much of Japan's northeastern coast, efforts to fend off future disasters are focusing on a nearly 400-kilometer (250-mile) chain of cement sea walls, at places nearly five stories high.
IIRC the Dutch found out that they need to have a wall against the whole seacoast, and that there will stll be seepage around the edges.
Richmond Va built a flood wall that covers every part of the downtown and riverfront industrial area that is lower than X feet above mean flood stage in areas that have a history of financial and/or structural damage over the last 100 years. The parts that are not protected are upstream of the downtown/industrial area and the river overflowing its banks reduces the amount of water that gets channeled between the floodwalls. The venturi effect that happens when the river reaches the narrowed spot just moves the damage downstream to the communities on the lower James that were used to the flooding in Richmond slowing down the current.
I'm thinking that King Canute-san may come to regret parts of this plan.
stay safe.
