Experience with embankment dam safety evaluation in Alberta

Following a rash of dam failures in the 1970s, many jurisdictions responded with the implementation of both legislation and regulations mandating dam safety evaluations. Almost all dams in Alberta are embankment dams, of which failures are mainly caused by: overtopping during flood discharge due to inadequate spillway capacity or non-functioning floodgates; internal erosion along the dam foundation interface; non-homogeneity in the foundation or dam, leading to foundation failure or erosion; large settlements in the foundation; cracks following settlement, with resultant piping; and liquefaction. Summaries are presented of a series of case histories of dam safety evaluations conducted in Alberta where the outcome was not routine. The case histories describe evaluations carried out at the following dams. The Bighorn hydroelectric development was completed in 1972, and measured seepage was found to be ten times greater than a recommended alert level. Dam safety evaluations concluded that the performance of the dam and concrete cutoff wall is satisfactory, but the owner reads all monitoring instrumentation on a regular basis and seeks on-going review from consultants. The Three Sisters Dam is a 21 m high homogeneous embankment hydroelectric dam. Very large seepage flows were found, and although remedial measures have been effective, extreme vigilence with an intensive inspection and monitoring program is required. Other case studies detail seepage monitoring at the St. Mary Dam, complex seepage patterns at Waterton Dam and Tavers Dam, and material durability studies at Hartung Dam and Murray Dam. The importance of good records and construction and performance histories is emphasized. 12 figs., 10 refs