Go westbound on C-470, you'll cross under Santa Fe (US Hwy 85), then cross over the South Platte, about 1/2 mile down there is a turn-off on the right for the riverfront parking lot access...follow that back and don't park where they say not to, you WILL get a ticket.
If the river is running at above 500 cfs coming out of Chatfield, you can run all the way to Confluence, but I'd recommend 800 cfs for that.
Some man-made drops you need to be careful on:
3 double drops about 1 mile north of Mineral? or Jackass Hill? can't remember the road, it's East/west though and will be the first road you cross under.
The first double drop at 500+ cfs can develop a nasty V-wave that will flip you if you're slacking on paying attention.
The second one has a rock out from the middle of the lower part.
The third can pin you if you're not careful.
Be careful on the last drop, backwashed concrete hole
Denver Water & Sewer Offices (roughly where 2nd Ave would run into I-25)
This drop should be scouted well at flows above 750 cfs, it's a triple drop ramp, there are jagged rails, and other weird shite in the holes like rebar.
At 1200 cfs this place becomes a monster, and you damn well better be on your game. It's a big nasty rapid and I have personally seen and ran V-waves on this that were 6 to 8 ft high and pulsing with the flow.
This is a mandatory portage unless they found the old ramp safety net.
The rest is cake