The spillway can be gradually eroded by water flow , including cavitation or turbulence of the water flowing over the spillway , leading to its failure . It was the inadequate design of the spillway and installation of fish screens which led to the 1889 over-topping of the South Fork Dam in Johnstown , Pennsylvania , resulting in the infamous Johnstown Flood ( the " great flood of 1889 " )
Johnstown Flood
Johnstown Flood
Dam