Source : Webster's Revised Unabridged Dictionary (1913)

Runnel \Run"nel\, n. [From {Run}. Cf. {Rindle}.]
   A rivulet or small brook.

         Bubbling runnels joined the sound.       --Collins.

         By the very sides of the way . . . there are slow
         runnels, in which one can see the minnows swimming.
                                                  --Masson.

Source : WordNet®

runnel
     n : a small stream [syn: {rivulet}, {rill}, {run}, {streamlet}]