The Possible System Caspian Sea Volga River Black Sea

What we propose is to maintain the current level of the Caspian, not through the waters of the Volga, but with those of the sea. To do this, we must put in communication Black Sea and the Caspian, opening a channel through the 700 km isthmus of Manich.
Then the waters of the Volga, instead of being used to create the Caspian, could be used to irrigate the large alluvial regions, below the level of the seas, but above the Caspian coasts. The waters of the great river could be distributed to the right and left, giving irrigation to a region of 20 million hectares, 200,000 km2.
At the same time, the channel that would unite both seas would not only serve to replace the Volga in its mission of maintaining the Caspian, but would play the role of a navigation channel, since the slope between the Black and the Caspian is 30 meters, that in 700 km they have an average descent of 0.042 meters / km, that is to say, 0.42 meters every 10 kilometers. Approximately one meter every 23 km. The drop allows perfectly the existence of a navigation channel without exclusives of any kind.