Erosion time scale in pipes below dikes for turbulent and laminar flow

ABSTRACT This article discusses the piping erosion time, where pipes start to erode in aquifers underneath dikes and dams until they reach their critical values. The magnitude of the piping erosion time significantly determines the risk of failure of water defences. The time-scale equation is based on a sediment mass balance equation and appropriate bedload transport predictors, assuming the erosion process to be continuous. We argue that the flow is laminar for pipes in sandy aquifers and turbulent for pipes in gravel aquifers. We then account for aquifer composition in examining pipe erosion by discussing different bedload transport predictors for each flow regime. To estimate the turbulence intensity, we have used and modified the Einstein bedload transport theory. The time-scale relation includes the effects of meander bends and has been tested for some experiments on a small scale and on a large scale.