Tough math calculation

[P3D]

Borys, the Don has an average flow of 935m/s. And I suspect it is at the estuary, i.e. downriver of the the Donets. While your canal is upriver.
The amount of the inflow the diverted Don generates would just evaporate. It would eventually increase the 371,000km2 Caspian sea by 20-30,000km2 (while the Caspian Depression has 200,000km2 area), but that's only 3-4m sea level increase.

The area of the Caspian Sea changes by the evaporation. If the climate is cooler (Ice Age), it rises.

[Borys]

Ahoj!
No, the canal would be at the estuary.
The Volga-Don canal is an awfull engineering project. It goes up from sealevel (at Tsaritsin) up to 88 metres, and then it goes down 60-something metres down to the level of the Don at this point. Tough rocks there.
The canal I am fantasising about would run along the Kuma-Manych fault line. Miketr once found a couple of maps of it. 
http://encarta.msn.com/map_701511583/Caucasia.html
Basically, it follows the boundry between Stavropolskiy Kray and Kalmukia. Which is straight, see? And it extends in a stright line towards Rostov in one direction, and the Caspian in the other.
Enlarging the Caspian mostly increases the surface of the northern portion, where evaporation is weaker.
But I suspect you are correct that I'd need more than a Don equivalent to fill the Caspian depression ... sniff, such a lovely idea ... more dynamite?

Borys

[Valles]

If it could be done then the increased rainfall in its shadow should do wonders for farmland fertility. Might well be profitable...

[P3D]

500km long, 150m wide, 15-20m deep, and the sea would cover a lot of desert - not prime real estate but still. Diverting the Ob would be a better idea.

[Korpen]

Ahoj!
No, the canal would be at the estuary.
The Volga-Don canal is an awfull engineering project. It goes up from sealevel (at Tsaritsin) up to 88 metres, and then it goes down 60-something metres down to the level of the Don at this point. Tough rocks there.
The canal I am fantasising about you run along the Kuma-Manych fault line. Miketr once found a couple of maps of it. 
http://encarta.msn.com/map_701511583/Caucasia.html
Basically, it follows the boundry between Stavropolskiy Kray and Kalmukia. Which is straight, see? And it extends in a stright line towards Rostov in one direction, and the Caspian in the other.
Enlarging the Caspian mostly increases the surface of the northern portion, where evaporation is weaker.
But I suspect you are correct that I'd need more than a Don equivalent to fill the Caspian depression ... sniff, such a lovely idea ... more dynamite?

Borys

The question that I am really curious to know to answer to is: "Why?"

[Borys]

Ahoj!
WHY?
- playing God is fun!
:)

And opening the Volga basin to maritime traffic is good for the economy.

Tsaritsin would be a booming seaport.

The possible "wettening" of the Orenburg steppes is a side benefit.
Borys