Detailed, theoretical analysis of the structure of water rivulets on inclined stainless steel plates is presented. Experimental results clearly demonstrate the variability of the width and height of a rivulet as a result of changing liquid flowrates within the flowing rivulet. Predicted results generated using the Laplace equation for curved interfaces combined with the Navier-Stokes equation characterize the flowing rivulet by establishing the expected, the maximum and the minimum dimensions of a flowing rivulet. The predictions also show that a simplified film model describing rivulet dow, which is often used as an approximation to the full rivulet model presented here, is inadequate.