Another secret of the Cumberland Plateau, Mammys is a full day adventure. There is a large pullout that makes a fine launch spot, and the creek is class II for a couple of miles, then II+. Then she turns class III with some sections becoming fairly continuous at good flows. The river a variety of tributaries contribute flow and broaden the riverbed, changing the character of the run.
There are lots of trees and brush in and around the creek, and constant vigilance for strainers is a must. Expect to duck under / hop over logs and make some tight maneuvers around wood obstacles. There are two drops that might be considered class III+ or IV- where the river slides and drops over ledges. The first slide type rapid has a rock in the hole where you might normally run it. This ledge is an easy scout and/or portage on the flat shelf on the right--unless the water is on the shelf, which would be high water. The second steeper ledge is on a left bend and has a tongue on the left if you can find it.
There are about 5 miles of Mammys before you the confluence with the Tiny Piney (Piney Creek) which doesn't seem so tiny when it joins from the left and quadruples the flow. The whitewater changes character with the larger streambed and volume but is no more than class III from this point to the takeout. Fall Creek comes in soon on the right with a similar volume to what you had in Mammys. A couple more miles downstream is the confluence with White's joining from the right, and then you are on a big river with the sandstone cliff vistas typical of the plateau.
Surf city is a set of ledges downstream of the Piney/White's confluence that form a variety of surfable waves and holes, some with eddy service. From this point downstream there are a few more II-III's then the whitewater tapers down until you reach the White's takeout on the left under the highway bridges.
Regarding flows, a deeply saturating rain will be necessary to bring this creek into a runnable range. There is a foot gauge at the takeout on White's Creek which read 4.0 before launching and 3.0 after taking out on a recent run with good flows. The gauge is painted on the upstream side of the bridge piling and this reading is taken on the side of the piling, rather than at the top of the water pile. It would probably be runnable at 3.0 before launching on falling water. There is a USGS gauge on White's but I have no information about correlations.
It may be wise to leave your valuables at home or carry them with you as breakins do occur.