Backward erosion piping is a leading cause of levee failures, second only to overtopping, and is therefore of great concern to engineers involved in flood control. Backward erosion piping refers to a process by which shallow erosion channels propagate upstream through foundation sands beneath water-retaining structures. If the erosion channels reach the upstream source of water, the channels rapidly enlarge, which can ultimately lead to collapse of the structure. Observations from the Mississippi River indicate that most erosion incidents do not lead to failure. This may be in part due to the slow rate at which backward erosion piping advances, as observed in laboratory experiments. Unfortunately, very limited research has been conducted on backward erosion progression rates, making it difficult to assess the timing of development. This study evaluates the progression rate of backward erosion through analyses of small-scale flume experiments conducted on nine uniform sands with median particle diameters ranging from 0.30 to 2.52 mm. Results indicate that pipe progression rate is proportional to seepage velocity, but is also influenced by particle diameter and void ratio of the sand.