I DO believe that the flat red oxide colored surface visible in the lower right central portion of the pic IS the core / headwall of whatever the hell that's supposed to be.
....a "spillway", emergency or otherwise, it sure as hell AIN'T,....

GTC

Member, Clan of the Border Rats
-- “Sometimes I wonder whether the world is being run by smart people who are putting us on or by imbeciles who really mean it.”- Mark Twain