As soon as a reservoir is filled, a dam begins its journey toward inevitable failure. Not necessarily catastrophic failure… in fact, that is very rare. But most dams experience some form of failure in terms of seepage or settlement… tiny incremental damage that accumulates over time, resulting from unrelenting force and sometimes poor design or construction.
Seepage can occur through, under, or around a dam. Although the actual volume of seepage may be negligible, the resulting damage can be substantial. Even small seeps can scour their path into major conduits, leading to larger flows, weakened structures and foundations, and potential settlement.
Settlement results when underlying formations are consolidated under the enormous weight of the dam and water. Differential movement causes cracks in concrete dams and planes of weakness in earthen dams… critical structural compromises.