I can confirm, they are definitely ripping out the concrete channels before filling them in. I was worried that they were just filling over it when I first saw photos. Once I got down there, there was an excavator with a hydraulic hammer and claw, ripping through the channels and putting the rubble in trucks to be removed. There was still water in the reservoir and in the channel that used to run under Eureka but they were in the processing of pumping that out when I was there too. Granted, the water level is fairly low, so they've already drained a heap of it.
Maybe they are doing the ol' switcharoo? Take the dirt from WWW and put it in Gold Rush, then take the water from Gold Rush and put it in WWW? 😂
Oh and I have no idea what @themagician was talking about because the reservoir or at least the deepest main part of it, is still very much there. (The part where rafts used to float into before they installed the gate)