Lessons from a Dam failure

The IVEX Dam (Chagrin River, northeastern Ohio) failed catastrophically on 13 August 1994, releasing 38,000 m(3) (about 10 million gallons) of impound ed water and sediment. This event was triggered by a 70-year rainfall event (13.54 cm of rainfall within 24-hours), resulting in flows 1.9 m above the top of the spillway and impinging on the top of the dam. The failure was t he result of seepage piping at the toe of the dam, near the masonry spillwa y-earthen dam contact. Eyewitnesses reported that collapse of the seepage p ipe created a breach in the dam that rapidly downcut. Paleohydrologic model ing suggests peak discharge through the breach was about 466 m(3)sec(-1), s ubstantially dewatering the reservoir in approximately 2-3 minutes. The effects of failure included erosion, flooding, and sedimentation downst ream, and erosion of fine-grained sediment within the reservoir itself. Of the accumulated reservoir sediment, 9-13% was mobilized by dam breach and c onsequent incision (as the Chagrin River re-established its gradient by dow ncutting through reservoir sediment). Of this amount, 61-86% was trapped in a downstream reservoir (threatening the integrity of this structure). The failure of this dam can be attributed to a large hydrologic event and t he combination of several factors: 1) inadequate spillway design, 2) lack o f an emergency spillway, 3) 86% loss of permanent pool capacity due to 152 years of sedimentation, and 4) poor dam maintenance resulting in seepage pi ping failure. Similar dam failures will become an increasing societal probl em, due to the aging of the nation's 75,591 larger dams and reservoirs, of which 95% are privately owned and operated.