Shot some bark and cranked it through 90 degs. Kind of looks like flowing water:
But still looks like what it is, so had at it in the GIMP.
Applied the 'Blur Motion' filter at a high length and a slight angle to give a direction of flow.
Then used 'Wavelet' processing to increase the high level details such as 16 and 32px, also cranked the residual's contrast to give more separate large areas.
Then set about 95% opacity to bring back a smidgeon of the original detail.
