I presume Rolihlahla Walden meant a 1 in a 150 year drought.

But while we're nitpicking details, you make the statement that "CPT added less than 20% dam storage in the past fifty years"  which is patently wrong.  Tweewaterskloof Dam was opened in 1980 with a capacity of 480 Glt and Berg River Dam in 2009 with a capacity of 130Glt.  The other dams serving CPT total 288Glt therefore the dam capacity increased to 311% of that of 37 years ago!