Estimation of Flow through and over Armored Slopes

Models developed for the transient routing of intense rainfall on small armored slopes depend on expressions for flow resistance below and above the surface of the armored layer. A series of 52 experiments are conducted in two flumes to collect data on the basic relationships of flow resistance. Crushed rock of 26‐155 mm median diameter is placed on embankments with slopes ranging from 0.01 to 0.2 and subjected to steady flow in the flumes. Flow through the rock layer is found to be approximately proportional to the rock‐layer porosity, the square root of the slope, and the mean diameter of the rock, and weakly proportional to the stage. The portion of flow through the filter layer generally cannot be neglected. Flow resistance decreases and conveyance greatly increases when the stage exceeds the depth of the rock layer. A model for flow both beneath and above the rock surface on an armored slope is synthesized from formulas developed for flow in rubble dams and Darcy‐Weisbach formulas developed for flow in gravel bed streams and mountain rivers. The results of the model compare favorably to the experimental flow measurements.