The Collaborative International Dictionary of English v.0.48:

Tumbling \Tum"bling\,
   a. & vb. n. from Tumble, v.
   [1913 Webster]

   Tumbling barrel. Same as Rumble, n., 4.

   Tumbling bay, an overfall, or weir, in a canal.
      [1913 Webster] Tumbrel