Minor Flooding in Ulster County

We got a little bit of rain a couple of days ago on Sunday night into Monday, December 17-18 from a coastal storm. In my area, it seemed to have dumped almost 4 inches of rain in less than 24 hours which led to some flooding in the area.

Here are a couple of graphs from the United States Geological Survey (USGS) stream gaging station on the Rondout Creek at Rosendale near where I teach at SUNY Ulster. You can see the pretty dramatic rise in of the stream from 10.25 feet at 8:00 pm Sunday to 19.5 feet at 3:30 pm Monday – 9.25 feet in 19.5 hours or almost half a foot per hour. That’s why the National Weather Service issued flash flood alerts Sunday.

The next graph shows the discharge of the Rondout in cubic feet per second (ft³/s or cfs). This seemed to peak about a half hour earlier than the height but again we see a fast increase from 700 cfs around 8:00 pm to 15,800 cfs at 3:00 pm the next day. That’s an increase of 22.5 times the volume of water going past the gaging station each second in less than a day.

How does this compare to other flood events on the Rondout? I actually have physical geology students at Ulster look at decades worth of data from this local gaging station (available at https://waterdata.usgs.gov/monitoring-location/01367500) to work out a recurrence interval vs. discharge graph as shown below.

From this graph (blue lines intersecting the red best-fit line to the data), we can tell that a discharge of 18,500 cfs might occur, on average, every 6-7 years (the bottom scale may look odd because it's a semi-log graph). Not a major flooding event, but certainly significant – especially for people who build their homes on river floodplains or along normally-sleepy mountain streams which is common in our area.

One place in Ulster County which always floods (almost yearly) is Route 299 and Springtown Road just west of New Paltz on the other side of the Wallkill River. As seen on Google Maps.

The fields there are a natural floodplain of the Wallkill. That’s a great place to grow corn and other crops but a lousy place to build. The road was, as expected, flooded on Monday, December 18. Lots of pictures shared on Facebook. Someone got a drone show showing minor coverage of Route 299 but Springtown Road completely underwater. By the way, obey the barriers and don’t drive through stuff like this, a woman in Catskill lost her life by driving into floodwaters Monday up there.

What’s neat is that I also saw a picture on Facebook from the Woodbury Historical Society from the 1920s showing the exact same place flooded 100 years ago. That’s looking across the Wallkill from the New Paltz side with the bridge to the left. Notice the faint Skytop Tower on the ridge.

These fields have been flooding as long as there’s been a Wallkill River here (it’s not called a floodplain for nothing!). Flooding is, unfortunately for the people who have to deal with it, a natural part of a river’s life.