What would be the reason to ask me about BS which you propose? As if the answer would not be obvious. Dikes all around Russia? No necessity at all, Russia is essentially a continental power. What makes sense, see here, would be to protect the whole Baltic Sea by a dike from Denmark to Sweden. Here all states bordering to the Baltic Sea would cooperate if necessary. Similarly, one could think about protecting the Black Sea as a whole with a dike protecting Istanbul. That would be, in both cases, not much to cut. What else? Vladivostok? That would be 20 km with water depth less than 20 m, no problem. Murmansk? 2 km 20 m. Everything else is quite irrelevant. In fact, even all those proposals for the Baltic Sea and the Black Sea would be quite irrelevant for survival of humanity - it would be some sort of luxury, protecting some historically important towns, with a lot of tourism and so on. From this point of view, it will be a good investment. And, don't forget, this would be necessary in a few thousand years, and only if Antarctica ice melts completely. Before this, sea levels rise at most 3-4 m per 100 years. Or 3-4 cm per year. A biblical thing, indeed. What I have written about salt you have obviously not read, or were unable to understand. There is no need for salt filters at all. Salt is a problem of very arid regions. If there is more precipitation, the salt will be washed out and flows with the rivers down to the oceans without any need of human participation.