HURRICANE AGNES and the GENESEE RIVER FLOODING
The most destructive, widespread flooding to occur in the eastern
United States occurred in June 1972 as a result of Hurricane Agnes. Unlike
some other flood producing hurricanes in the northeast, Agnes was not
a particularly strong hurricane. In fact, most of its devastation occurred
well after it had been downgraded to a tropical storm. Agnes originated
in the Gulf of Mexico and slowly moved up the east coast before moving
northwest across Pennsylvania and the southern tier of New York state.
At this point, the remnants of Agnes joined another large low pressure
system and continued to produce heavy rains.
The most significant destruction caused by Agnes, occurred in the Susquehanna
River basin in Pennsylvania. This is well documented by the NWS Middle
Atlantic River Forecast Center. This description will focus instead on
the impacts on the Genesee River basin in western New York.
During the week prior to Agnes, a large amount of shower activity resulted
in widespread areas of over an inch of rain. Heavy rain from Agnes started
on the night of June 20 and continued until the 25th of June.
Over the Genesee River basin, the maximum official rainfall amount recorded
was 13.7 inches at Wellsville NY. Unofficial reports of over 16 inches
were also received.
On the upper Genesee, above Mt Morris Dam, flooding was devestating breaking
all historical records. Both of the official river stage gages -- at Scio
and Wellsville -- were destroyed by the flooding. Hundreds of roads and
bridges were washed out by the flood waters. One significant factor in
the damage was the large amount of debris flow that moved downstream which
caused significant scour and damming along various parts of the stream
channel. The Wellsville area was the hardest hit in the Genesee basin
as a portion of Jones Memorial Hospital was destroyed by the flood.
The lower Genesee mainstem, from Mt Morris to Rochester, was spared the
worst of the flooding primarily due to the operations of the dam. During
the early part of the event, there was significant concern of overtopping
the spillway or having to release such major amounts of water as to cause
major downstream flooding. Overtopping would have been catastrophic in
terms of flow, but also would have allowed significant debris that was
caught by the dam to be released downstream. However, close monitoring
and careful releases resulted in flooding downstream but not nearly to
the impact that could have occurred. Maximum inflow to the reservoir was
about 90,000 cfs; however, the outflow was limited to just over 15,000
cfs. While downstream damage did occur, the Corps of Engineers estimated
that the dam operations during Agnes alone prevented over $200 million
of additional potential damage.
Downstream flooding was also contributed to by tributaries, such as the
Canaseraga Creek. Downstream of Dansville, flood levees were overtopped.
The levees, which were designed to protect agricultural land, wound up
causing problems since it took nearly all summer to drain the fields following
the flooding.
| River | `Location | Flow | cfs/sq mile | Stage |
| Genesee | Wellsville | 38,500 cfs | 134 csm | 20.7 ft * |
| Genesee | Portageville | 90,000 cfs | 91 csm | 35.2 ft * |
| Canaseraga | Dansville | |||
| Genesee | Avon | 16,500 cfs | 10 csm | 40.7 ft * |