If I had to guess, it depends on how the soviets handled the two biggest challenges with geoengineering: evaporation and salination of the water due to the evaporation revealing and releasing minerals from the soil that the water then dissolves into it. These problems are compounded when the area is traditionally drier and water is scarce, since over doing it can lead to what our little Squanderer here will refuse to admit; it can utterly ruin what agriculture you do have and rapidly desertify regions that otherwise were better off.
Case in point, the Murray River going bone dry on the regular now due to all the evaporation and run off due to the cost cutting measures that Aussie contractors put in to match their super low underquote. A drip system similar to what China does in their western provinces in areas like Gansu or Qinghai for example would have helped quite a bit with evaporation at the very least. Larger amounts of desalinization plants would also be very useful, as what Libya and Egypt do.
The Soviets, given their track record with even simpler projects such as the Grand Electrification Program, would probably have screwed it up and nuked the fishing industry that makes up a good deal of the profit (and diet to a degree) for Kazakhstan and Uzbekistan. Heck, they almost did with their rainmaker program in the 1980s, since the run-off caused a pretty bad die-off of the fish population and polluted the water.