Most of this information is confined within the twitter thread, however, I think it is important to clarify some of this here. May 15th was a pretty normal Sunday. I was inside of the geosciences building on the Union College campus in Schenectady when a pretty strong rain storm passed by. While this event was brief, it dumped somewhere between 0.81-1.1 inches of rain. Now in the grand scheme of things this isn’t actually that impressive. This kind of hourly rainfall event has a recurrence interval of 1-2 years. Sadly, the weather station on campus was not recording 5 minute intervals at the time, but I suspect this must have all fallen in a fairly short time to elicit the response you are about to see.
Within 15 minutes of the end of the strongest rainfall rate, my friend and I decided to take a walk around campus to see if there was any flooding near storm drains. To our surprise we could hear an immense rushing noise coming from the usually small and sleepy stream on campus. As we got closer we could hear the clacking of large rocks being transported in water. When we finally made it to the stream this is what we saw.
Wild series of event transpired in #Schenectady a few hours ago. Strong thunderstorm rolled in and dumped 0.81-1.1 inches of rain in an hour (according to the data from 2 stations). This kind of event had a RI of 1-2 years yet it resulted in #flooding of a usually <20 cfs stream pic.twitter.com/4TSOgunljE
— Ian Plummer🇮🇹🏴 (@plumquat) May 15, 2022
To help contextualize how crazy this event was, I included images of a previous extreme rainfall event that resulted in what we considered to be fairly high discharge. You can see how much this event dwarfed that.
Here’s an image from back in Sept when heavy rainfall raised the stage to what is usually considered high flow. Next to it is an image of the same bridge from the side (use the rocks as reference) pic.twitter.com/QBZuKSigLK
— Ian Plummer🇮🇹🏴 (@plumquat) May 15, 2022
The final portion of this thread juxtaposes an image of the typical base flow of this small stream with an image from this flood. You can see in the left hand image that the channel is somewhat cut into the soil and bedrock. This event really puts context into how those large sandstone slabs get moved around. While I wasn’t able to capture it on video, we kept hearing the eerie thud of hundred pound rocks clashing together in the torrent of water.
Here’s an image from last fall to give an idea of what the mean state of the stream usually looks like. Next to it is the same bend in the river but from outside the channel for obvious reasons. pic.twitter.com/tDRY0dOVqd
— Ian Plummer🇮🇹🏴 (@plumquat) May 15, 2022
While this event was localized and didn’t really produce any massive infrastructure damage, it highlights an ongoing problem in Schenectady and many smaller urban communities. Research done by professors at Union has shown that there is clearly input of sewage water after these large rainfall events. The water you are looking at in that video is a large part raw sewage. This water was tested and analyzed within labs at Union College. While these problems are being slowly addressed, it is unclear how many streams in the region face the same problem. This all becomes additive, as these streams feed the Mohawk River and shallow aquifers that Schenectady uses for communal water. The same study done at Union College also showed that there is a clear sewage input in the Mohawk River during these same events. We are also seeing signs of there being a correlation between these rainfall events and outbreaks of GI illnesses in the campus and city comunities. So a small stream running through a quite liberal arts campus can signal larger issues facing the community.