Spillways, Sinkholes, and Slope Failures: Quick Thinking Saves Two Dams

EXTENDED ABSTRACT ONLY - In the Winter of 2020 and Summer of 2021, two significant hazard potential embankment dams located in suburban Massachusetts towns required emergency response efforts to avoid what could have almost certainly resulted in failure of either dam. Although unrelated, the similarities shared between these two near-failure incidents underscore several important considerations and ‘lessons learned’ that the dam safety community has come to emphasize in recent years.
In late December 2020, staff involved with the regular surveillance and maintenance of facilities at the Massachusetts Correctional Institute in Norfolk, Massachusetts observed that an apparent sinkhole had developed along the downstream side of the crest of Industries Drive Dam. The dam consists of an earthen embankment approximately 1,000-ft. in length with a structural height of approximately 18 ft. The dam has a primary spillway, but no auxiliary spillway or low-level outlet.
Based on the conditions observed, the sinkhole was subsequently backfilled by the facility using lightweight controlled density fill as a stabilizing measure. However, within a period of days an additional sinkhole developed adjacent to the original location and engineers at Weston & Sampson were contacted to visit the site since conditions appeared to be worsening. Based on conditions observed during the site visit, it was apparent that a significant void had developed which extended vertically from the downstream side of the dam crest to the base of the dam. In response to the continued deterioration, engineers, contractors, state dive team representatives and state dam safety officials mobilized to the site on Christmas Eve to further evaluate and stabilize conditions prior to the forecasted arrival of heavy rains on Christmas Day. (CONTINUED...)