Seepage Surveillance & Monitoring

Active seepage situation at the toe of a dam.

Nearly every dam experiences seepage to varying degrees. Depending on the type of dam and its unique site conditions, seepage may go through, underneath, or around the dam. When left unchecked, excessive seepage can lead to problems such as internal erosion and eventual failure of either the dam itself or other vital components of the dam. According to the Association of State Dam Safety Officials (ASDSO), the second most common dam failure incident driver between the years 2010 through 2019 was seepage or internal erosion.^[1]

As a result, monitoring the level of seepage experienced by a dam is essential to building a performance history of the dam season to season and year to year against which future observations can be compared. Should anomalies in the real-time seepage data occur, having a well-documented history can help operators, owners, and engineers determine the cause of these anomalies and if they are cause for concern.

“If uncontrolled seepage is observed, then it should be monitored. To monitor seepage, the following should be recorded: the location of all seepage exit points; seepage flow rates and clarity; the occurrence of recent precipitation that could account for what appears to be seepage, or that could affect the appearance and quantity of actual seepage; the level of the reservoir at the time of the observation. Notes, sketches, and photographs are useful in documenting and evaluating seepage conditions. The amount of seepage usually correlates with the level of the reservoir. Generally, as the level of the reservoir rises, the seepage flow rate increases. An increase in a seepage flow rate for a similar reservoir elevation is cause for concern. In some cases, dye can be used to confirm that the reservoir is the source of seepage. A dye test is not a routing procedure. The length of time it takes to conduct a test may vary since the dye may take different amounts of time to penetrate the embankment or foundation. In most cases, records of seepage volumes that correlate with reservoir elevations are needed to show that seepage comes from the reservoir”.^[2]

“Seepage collection and discharge systems, including structural drainage systems, must include access points. Construct these systems in a manner that permits inspection and cleanout of drainpipes. Collection systems should include sediment traps and seepage measurement devices such as weirs or flumes, unless excluding these features is justified in design documentation”.^[3]