Anatomy of a flood

The height or “stage” of a river is measured by instruments called gages that are located permanently at various sites in the river. The number registered by the gage, in feet, is the height of the water from the bottom of the riverbed at that point. The bottom of the riverbed at the Barryville gage is 600.22 feet above sea level; at the Callicoon gage it is 734.88 feet above sea level. The information collected by the gages is beamed to a satellite and then transmitted back down to data collection centers.

Flood stage is the level at which a river overflows its banks onto the flood plain. Naturally, the exact number that counts as flood stage varies with the surrounding topography. At Callicoon, a gage measurement of 12 feet is considered to be flood stage. At Barryville, flood stage is 17 feet.

The accompanying graphs chart the gage measurements at Callicoon and Barryville against time. They show the river passing flood stage in Callicoon at about 6:30 in the morning on Saturday, September 18, with the gage at Barryville registering flood stage almost two hours later, at about 8:15. Oddly, Barryville peaked first at about 2:30 p.m. and 24.08 feet. This is more than seven feet over flood stage, but still less than the record 26.4 feet recorded during the flood of 1955 that accompanied Hurricane Diane. The fact that downstream Barryville peaked before Callicoon may have been related to backwash from the Lackawaxen, Bruce Krejmas at the United States Geographical Survey’s (USGS) Rivermaster’s Office said.

The Callicoon gage reached a peak of 17.33 feet at 4:45 p.m. It was the highest number ever recorded at that gage, which was installed in June of 1975. A record was also recorded in the East Branch at Fishs Eddy, where the gage has been there since 1912, and at Cooks Falls on the Beaverkill, where measurements have been taken since 1913, the peak fell short of a record by only two-tenths of a foot.

According to the USGS, in much of the Upper Delaware River area, this flood exceeded the standards required to call it a 100-year flood, a flood event that statistically has a one out of 100 (or one percent) chance of being equaled or exceeded on a specific watercourse in any given year. A flood event of this magnitude is often used to determine if flood insurance is either advisable or required on a property.