Hi Chris
I have wrestled w the same problems as I build maps for the Il-2 Shturmovik computer air combat sim game. First, let me caution you about the maps in the pre-war series. They date from the 1920's and are often out of date for the 1940's. Badly.
Uncle Joe was really into hydro electric and irrigation projects and created a number of dams and reservoirs in Ukraine. The challenge is figuring which were / were not built by the time of WW2. The Dnepr looked very different in 1925, 1940 and 1960.
John's site also contains some 1:250,000 maps drafted by the US Army Corps of Engineers in the late 40's which are more period-accurate than the prewar 1:50,000 maps. I d/l-ed maps for DP, Odessa, Melitopol and Krivoy Rog. I suspect the rest of the series might be available elsewhere on the Net.