It wouldf be interesting to see some links showing these arrivals to dam. Maybe I don't follow Russian telegram channels enough and maybe I missed it, but I don't remember such complaints from Russian side
I have collected for you links from Russian-language resources in chronological order with Russia's statements about the shelling of the Kakhovka hydroelectric power station by the Armed Forces of Ukraine. link1
link2
link3
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But as far as I understand, the only evidence that has weight for you is the confession of Major General Andrey Kovalchuk, who at that time commanded the Armed Forces of Ukraine in the Kherson region, made by him in an interview with the Washington Post.
Still, destroying such dam with HIMARS, Storm Shadow or any other equipment that Ukraine have sounds unrealistic. If we talk about destroying it from outside, maybe FAB aviation bomn would be enough to blow it
Do you want to say that the Armed Forces of Ukraine systematically and regularly shelled this dam from expensive Western weapons for almost a year, without any intention and opportunity to destroy it? Just wasting charges for Himars? Sounds a little stupid. Try telling this theory to your US sponsors. 
Pretty much unverifiable and one-sided sources. Ukraine has not regularly shelled the dam. However, right now the RF is effectively destroying dams along the path of the Ukrainian advances near Makarivka, in Zapo region, just in case anyone could hold a doubt about this being a "modus operandi".
Curious how the propaganda machine is so disconnected from the RF Army.