Dam Safety Worked Examples

By Michael Flynn, PE · water resources & dam safety engineer

Four problems worked all the way through, on one structure. Most dam-safety references explain the equations or reproduce the rule; very little shows what happens when a real breach model meets a regulatory threshold and the answer decides whether a dam is jurisdictional. That handoff is where the work actually lives, so that is what these examples cover.

The rest of this series

These four examples follow one structure through the whole decision chain, because in practice that is how the questions actually arrive:

1. Breach parameters for a 22-ft earthfill dam — produces the failure hydrograph everything else depends on.
2. Class B or Class C? The 1.5-foot flood rise test — turns that hydrograph into a hazard classification.
3. Does an 18-ft farm pond dam need a permit? — the classification decides whether the size exemption survives.
4. Spillway design flood for a Class C dam — and the classification sets the storm the spillway must pass.

The structure they all use

A 22-foot earthfill dam impounding 145 acre-feet for recreation, with one occupied dwelling roughly 2,400 feet downstream — which describes a very large share of the 3,687 dams in North Carolina, where 91% are earthfill and recreation is the single most common primary purpose.