5‑Year Flood Event in Oliverea

Posted on: November 1st, 2021 by Tim Koch

The Eso­pus Creek head­wa­ters and Birch Creek both expe­ri­enced a 5‑year flood event as a result of heavy rains on Octo­ber 25th and 26th. The McKin­ley Hol­low bridge was briefly over­topped due to downed trees block­ing the inlet. Oliv­erea Road (Coun­ty Route 47) was closed for a num­ber of hours due to flood­ing in a low lying area where the road and stream are at the same ele­va­tion. Ulster Coun­ty DPW prompt­ly respond­ed to reopen the bridge and road. 

McKin­ley Hol­low bridge after large trees were removed from the inlet and placed on the down­stream side of the bridge. 
Ulster Coun­ty DPW crews at work reopen­ing a low-lying sec­tion of Oliv­era Road.

A 5‑year flood event is the dis­charge that has a 20% chance of occur­ring in any giv­en year, based on sta­tis­ti­cal analy­sis of at least 10 years of con­tin­u­ous flow data from a USGS stream gage. The “100-year flood” has a 1% chance of occur­ring in any giv­en year. 

The longer the peri­od of record at the gage, the more accu­rate the prob­a­bil­i­ties will be for a flood of a giv­en mag­ni­tude. The Ashokan Reser­voir water­shed is one of the most heav­i­ly mon­i­tored water­sheds in New York State, both in terms of the num­ber of gages and the length of time.

The Eso­pus Creek gage at Allaben has con­tin­u­ous flow data since 1968 (53 years) and the Birch Creek at Big Indi­an gage has been in oper­a­tion since 1998 (23 years). The Eso­pus Creek at Cold­brook gage has been con­tin­u­ous­ly mon­i­tor­ing flow since 1931 (90 years), with month­ly flow data dat­ing back to 1914, when the Olive­bridge dam and the Ashokan Reser­voir were still being constructed. 

USGS stream gage on the Eso­pus Creek at Cold­book, in con­tin­u­ous oper­a­tion for 90 years. Pho­to cour­tesy of USGS.

The Ashokan Water­shed Stream Man­age­ment Pro­gram is con­tin­u­ing to assess this flood event and assist­ing local high­way depart­ments with emer­gency stream repairs as request­ed. If you need advise on how to man­age flood­ing or ero­sion on your prop­er­ty in the Ashokan Reser­voir water­shed, call the stream pro­gram office at (845) 688‑3047.

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