With a graphic by Karl Anshanslin
The Margaretville Floods
Recently the Mountain Eagle ran a report on plans for a new Local Flood Analysis (LFA) for the Town of Margaretville. That will be overseen by the Delaware Soil and Water District. The purpose is to evaluate flood conditions along the East Branch of the Delaware River as it flows through Margaretville. If floods strike, which they certainly will, who will see the worst damage and is it possible to mitigate that damage? It’s been about ten years since the last time anything like this has been done, so it is needed. Neither of us has an extensive background in the geology of flooding, but we have had a fair amount of first-hand experience, including in Margaretville. We would like to describe our views on the issue.
The proposed flood analysis is a very good idea. Floods don’t just happen; it isn’t just a matter of heavy rain producing heavy flooding. There are other factors that determine exactly where floods strike and how bad they may come to be. Margaretville has long seen frequent flooding. The two of us went there in 2011 and saw the damage done by Hurricane Irene soon after it struck. In fact, we traveled all around the Catskills after that storm. We found that there was a common factor in all of the towns that suffered the worst from Irene. That commonality was the presence of geological features called alluvial fans. Take a look at our map (courtesy of Karl Anshanslin). That brown feature is the fan. Sediment carried by Bull Run, a creek that flows into Margaretville from the north, was deposited so as to create the fan at the end of the Ice Age. It has been there ever since. Critically, it has formed a significant narrowing of the valley – right there. Again, see red bars on Karl’s map.
It’s our judgment that during Hurricane Irene the Bull Run fan, because it narrowed the valley, created a partial block of the East Branch. Flood waters were squeezed into this blockage. Those waters were forced to slow down and that backed up the flow. A backed-up flow soon becomes a rising flow of water. And that became the flood. We first recognized this sort of phenomenon in Prattsville which also suffered similarly from Irene. Prattsville, like Margaretville, was built upon an alluvial fan. Soon we found similar fans in Middleburgh, Breakabeen, Delhi and other towns. All these sites saw post ice age fan deposition, and all faced similar flood threats. And because of this, all will certainly face floods in the future.
This is serious business; many flood threats throughout the Catskills are related to similar post ice age events. This is important geology, and all Catskills citizens should be aware of it. Now you are among them. Do you now feel just a bit enlightened?
Contact the authors at randjtitus@prodigy.net. Join their facebook page “The Catskill Geologist.” Read their blogs at “thecatskillgeologist.com”
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