Internal Soil Erosion

Illustration showing internal soil erosion inside an embankment dam where water seepage removes soil particles and forms piping channels

Internal erosion is the formation of voids within a soil caused by the removal of material by seepage. It is the second most common cause of failure in levees and one of the leading causes of failures in earth dams, responsible for about half of embankment dam failures.

Internal erosion occurs when the hydraulic forces exerted by water seeping through the pores and cracks of the material in the dam and/or foundation are sufficient to detach particles and transport them out of the dam structure. Internal erosion is especially dangerous because there may be no external evidence, or only subtle evidence, that it is taking place. Usually, a sand boil can be found, but the boil might be hidden under water. A dam may breach within a few hours after evidence of internal erosion becomes obvious.

Piping is a related phenomenon and is defined as the progressive development of internal erosion by seepage, appearing downstream as a hole discharging water. Piping is induced by regressive erosion of particles from downstream and along the upstream line towards an outside environment until a continuous pipe is formed. (Wikipedia)

Minimum Channel Grades: Why They Matter in Denton

Concrete stormwater drainage channel in Denton showing proper minimum longitudinal slope for positive drainage

According to the City of Denton Development Code (Drainage Criteria Manual), open channels must be designed with minimum longitudinal slopes to prevent standing water, reduce sediment buildup, and maintain positive drainage flow. In practice, engineers must carefully balance slope, velocity, and erosion control to ensure channels convey stormwater efficiently without causing downstream scour.

Flow Net

Flow net diagram showing groundwater movement beneath a dam with flow lines and equipotential lines in a saturated aquifer

A flow net is a graphical representation of two-dimensional steady-state groundwater flow through aquifers. The construction of a flow net is commonly used to solve groundwater flow problems where analytical solutions are impractical due to complex geometry. It is widely applied in civil engineering, hydrogeology, and soil mechanics, particularly for analyzing seepage beneath hydraulic structures such as dams and sheet pile walls. A flow net consists of a grid formed by drawing a series of equipotential lines and flow lines, making it an important tool for analyzing two-dimensional irrotational flow problems. The flow net technique is therefore a graphical method used to represent and study groundwater flow behavior (Wikipedia).