B:
The Nio is a stream that almost always has enough water: in fact, a really big thunderstorm that dumps 5" of water on the watershed will raise the river about 5" -- it is at the (relative) top of the Oglalla Aquifer (and in the Nebraska Sandhill region), so rainfall just seeps right into the aquifer and has relatively little effect on the river.
The river, being in Nebraska, is almost all privately owned, the main exception being between Cornell Bridge (a bit downriver from Valentine) ALMOST to Norden Bridge (actually, this take out is owned by the Nature Conservancy, but a call to them will get permission for you to take out there.) The rapid just above Norden Bridge is not runnable by sensible folks. From Cornell to Norden is about 31 miles, with accesses about 7 miles apart on average
Below Norden, the river may actually be paddled for another 40 miles, but is awfully braided (read REALLY shallow and sandy (i.e. you get to drag your boat a LOT)) and pretty uninteresting.
River gage:
https://nwis.waterdata.usgs.gov/ne/nwis ... 2017-09-20
Good info on the river:
https://www.nps.gov/niob/planyourvisit/ ... tubing.htm
Valentine is the only real town nearby and has groceries, eateries, gas stations and motels. The other "towns" marked on maps are pretty tiny.
The stream is spectacular and has good paddling most any time that the water is not frozen. The only two really inappropriate drops for open touring boaters are 1) at Rocky Ford (pretty interesting class III) and Norden Falls (serious Class IV or V.) The other drops are scoutable and portages are available.)
While you are in the area, if you like tiny streams, fast water and incredibly difficult shuttles, you should try the Dismal River: it is a hoot!
Check the National Weather Service for normal temps in the Valentine area for an idea of the needed paddling and/or camping gear.
If you need more info, email me...
HTH
al