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, including biofouling and mineral deposition, which results in reduced drainage function.

Two model drain systems have been constructed and operated with circulating water to induce biofouling and mineral buildup. These systems approximate the cross-sectional scale of functioning drains. One system (the Ohio model) uses relatively coarse matrix media and has been maintained as an intermittently flowing aerobic system. The second (the Denver model) uses a more complex and finer matrix around the drain pipe. Flow rate, cross-sectional head and water quality have been recorded over the months and years of operation.

The Ohio model has experienced biofilm development, including aerobic filamentous and nonfilamentous heterotrophs, but not iron-related or sulfate-reducing microflora. Although the stock water (local well water) used has a high iron content, the predominant mineral deposited in the matrix is calcite, resembling clogs in many Reclamation dam drain systems. There has been minimal head build up due to clogging in the Ohio model, but sampling ports have clogged. The matrix also efficiently removes iron and alkalinity from water within 30 min of recharge with new stock water.

The Denver model, also stocked with local well water, has clogged more quickly, developed iron biofouling, and altered water chemistry during operation.

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. Such models can be reproduced to resemble specific drain situations, and used to calibrate mathematical modeling of such systems.