LABORATORY SCALE MODELING OF DAM DRAIN CLOGGING COMPARED TO REAL LIFE

Functioning toe drains and relief wells are directly related to dam geotechnical function and safety. For many years, U.S. operators and managers of dams, including the Bureau of Reclamation, have been addressing the issue of drain and relief well clogging, particularly in aging dams. Such clogs include biofouling and mineral deposition. This deposition can result in reduced drainage function.

The authors conducted studies of aqueous geochemistry and microbiology for drain system water and clog deposits for several Reclamation earthen dams. Results included confirmation of the role of biological activity in clog formation, and alteration of aqueous chemistry along drain profiles.

Two model drain systems were constructed using expedient materials and methods and operated with circulating water to approximate the cross-sectional scale of functioning drains. Flow rate, deposit composition and water quality have been recorded over the time of operation and compared to site investigation results.

The models exhibited changes in water quality and deposit compositions analogous to those associated with field studies of dam drains, including changes in water mineral content, deposition of calcite, sulfur-oxidizing, iron and manganese biofouling and mineral deposits.

Clogging-associated head loss changes were also induced. The two models exhibited somewhat different results associated with their construction details.

The model systems have demonstrated that field-type dam drain clogging phenomena and responses can be recreated at the “bench” scale, much as they have been with wells. The clogged models are now available for cleaning tests to plan more effective drain maintenance. Such models can be economically reproduced to resemble specific drain situations, and used to calibrate mathematical modeling of such systems.