YouTube user Javier Cornejo has posted an interesting video of a scale model of a dam and how flow can seep through it.

The water on the upstream side of the dam has had dye added to aid in the visualization of the seepage through the dam.  Additionally, as the seepage has stabilized, a line has been drawn on the model wall showing the path of the water through the dam’s cross-section.

In this model, as the water reaches the base of the dam, its path is blocked by the floor of the model and then exits out the toe of the dam.  Generally seepage is expected at the interface of the backside of the dam and the toe, but, depending upon a dam’s construction, seepage can be encountered up the backside face of the dam.

Some amount of dam seepage is to be expected and designed for.  The seepage is monitored for both flow rate and composition to ensure that the dam is structurally sound.  Changes in either can be indicators of failure. 

Unlike most open channel flow monitoring applications, dam seepage applications call for the retention of sediments and solids.  These can be analyzed to see where the dam is experiencing seepage pass through.  Typically weir boxes are used to quantify / qualify the seepage, although HS / H flumes (with approach section inlet risers / sediment traps) are also used.  For larger flow rates, Parshall or Cutthroat flumes may also be used.

Source:  YouTube