You have, no doubt, heard about what happened to Prattsville during Hurricane Irene. The Greene County region received between 12 and 16 inches of rainfall and the flood waters of Schoharie Creek rose up and devastated the village. Homes were lifted up and swept away during the flood; many more were damaged beyond repair. My wife and I managed to get into the town just a week after the storm. We were warned that we would be shocked by what we would see and we were. We have known Prattsville and many of the people who live there. We have worked with the Pratt Museum and studied the geology of Pratt Rock. It’s a modest village, but we were always struck by how clean it was. You never saw litter lying along the road. People picked the stuff up; they had pride.
We were very sorry to see the mess the town had become, but heartened to see how determined residents were to recover from the devastation. My job was, of course, to try figure out what had happened. Prattsville has been flooded in the past, but probably never as bad as this time. The easy explanation was to just blame it on the heavy rains, but I thought there must be more. I would look and see.
I got my maps out and studied the topography. Hints began to emerge. Prattsville was not built upon a floodplain. It is spread out across a sizable fan shaped rise, and that lies upon the floodplain. Upstream and downstream, there is a broad flat floodplain but at Prattsville the valley is far more narrow. It’s that fan which helps to make it narrow. I found that something called Huntersfield Creek descends from the hill above, down to the fan. I immediately recognized all this as something called an alluvial fan.
Such fans are common throughout the Catskills. I have seen many of them before. As the Ice Age was ending, Huntersfield Creek, swollen with meltwater, had flowed down to today’s Prattsville and deposited the sediment of the fan. Millennia later the fan offered what seemed to be a favorable location to build the town. People didn’t know what an alluvial fan was; they just knew that its elevation would make flooding far less likely. They were right — for a century and a half — until Irene struck.
But when Irene struck the fan was of little value; in fact it may have done more harm than good. The fan created something of a bottleneck within the Schoharie Creek Valley. Take a look at the map and see how the fan stretches out, almost across the whole valley and forces Schoharie Creek up against the west side. That’s the bottleneck. Floodwaters encountered that bottleneck and they were slowed down and backed up by it. Then they were squeezed through the bottleneck itself and here they speeded up again. All this is just what happens when you squeeze a garden hose. You do it without thinking. You want a powerful flow of water so you squeeze the hose’s nozzle to create that much more powerful rush. That is what struck Prattsville. The flood currents were squeezed and raised up as they passed through the valley made narrow by the fan; at the same time they were speeded up and made much more damaging than they might otherwise have been. It was a one-two punch.
The effects were worst at the southeastern upstream and northwestern downstream ends of town. In the east, the rush of flood waters should have been deflected to the left, but momentum carried them straight into town. There a number of houses were badly damaged or, some of them, destroyed. The currents continued on, following Schoharie Creek around a great arc, encircling the Prattsville fan, before coming back to intersect the northwestern end of the village (see arrows on map). There more of the worst damage is seen.
The irony of all this is that the fan, which should have prevented the flooding, instead, made it all the more worse. I think of this as the garden hose hypothesis to explain what happened. The fan was supposed to be elevated enough so that flooding would never occur. Never say never!
There is a worse irony. I mentioned earlier the many towns are built upon alluvial fans, all throughout the Catskills. They include Cooperstown, Milford, Delhi and Palenville. All were located where they are because of the elevation that their alluvial fans afforded them. I have been describing this for years, mostly in articles in Kaatskill Life magazine. I had never doubted the wisdom of this, until Irene struck. Now I will have to go out and examine each of these towns again — in light of the August disaster. ++
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