Mississippi's Big Dig - Managing the Percy Quin Dam Incident

The Percy Quin Dam (also known as Lake Tangipahoa Dam) is located in Percy Quin State Park in Pike County, Mississippi. This is a state park located in the southern part of the state. The dam was constructed in the late 1930’s. The dam is 34 feet tall and impounds a 550 acre lake at normal pool. The top of the dam varies from elevation 338 to 340. The crest of the emergency spillway is at elevation 334.4 while the crest of the principal spillway is at elevation 329.4. The lake drain invert is at 314.5 while the streambed is at elevation 306. The lake is fed by the Tangipahoa River which then flows into Louisiana, 14 miles downstream of the dam. From there the river flows another 54 miles before emptying into Lake Pontchartrain. The drainage area to the lake is 48 square miles. There are 3 houses less than 2 miles downstream of the dam. These houses, which would be flooded in the event of a failure, were what led to the dam being classified as a high hazard dam when the dam safety program began in the 1970’s. Interstate 55 and Highway 51 cross the Tangipahoa River 5 miles downstream of the dam. In 2003 an emergency action plan (EAP) was prepared for the dam. The inundation map indicated several houses might be flooded in the event of a failure. However, the inundation map stopped at the state line so the extent of flooding, if any, into Louisiana was unknown.