You haven't read the stickies (????)
fimbulwinter post
3. Not river bluffing when it's hopeless and you've been betting. say you've been betting a flush and gutshot draw and its the river with 30 bucks in the pot and the probable drawer checks to you. almost all 25NL players check behind here and i can't say how many times two draws were shown down in these types of pots. the bluff doesnt and shouldnt be big, you just want them to lay down a higher nopair than you have. remember that this only has to work a small amount of time if you're betting 1/3 pot, and the times I try it i'd guess it works about 50% of the time, so take that EV.
This is kind of my thinking behind my river push here (yes I'm bluffing "big" - but I can't see less than a push here being called if villains spiked some crap pair on the turn/river given how big my stack is in relation to the pot)
Also if I check behind an observant villain will see what cards I'm betting with here - if he folds he doesn't get to see my hand.