History of Mount Morris Dam
Mount Morris Dam was authorized by Congress in the Flood Control Act of 1944, and constructed from 1948 to 1952 at a cost of $25 million.
Records show that severe floods had plagued the valley as far back as 1800. Terrible destruction resulted from the flood of 1865, which developed flows exceeding 24 million gallons per minute, one half the flow of Niagara Falls. From 1865 to 1950, a major flood ravaged the Genesee River valley on an average of every seven years. Completion of the project significantly reduced the risk of flood disaster which formerly threatened the lower Genesee River valley. The capacity of the reservoir in the river gorge, 301,853 acre-feet, is ample to protect the basin below from all but very infrequent floods.
Mount Morris Dam is operated to maximize holding capacity for high-water events. When river flows exceed the natural capacity of the downstream channel and flood damage is likely to occur, flood waters are stored in the dam’s reservoir. As soon as downstream conditions permit, the stored water is released gradually through the nine conduits at the base of the spillway sections. About 30 days are required to empty a full reservoir at a rate that would safely avoid damage to downstream properties. During periods of the year when little precipitation occurs, run-of-the-river levels prevail in the gorge.
In its first 50 years of operation the project has prevented damages estimated at over $1 billion. During Tropical Storm Agnes in 1972, $210 million in damages alone were prevented, primarily in the Rochester Metropolitan Area. At that time, the inflows exceeded the storage capacity of the reservoir and it was necessary to release water through the gates of the dam, causing minor downstream flooding. These releases were made to prevent overtopping of the spillway. Had the spillway overtopped, accumulated debris in the reservoir would have passed downstream, causing log jams and additional damages. An inflow of the magnitude of Tropical Storm Agnes is expected to occur on an average of every 300 years.