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Home Interpreting the Data HRECOS Stories HRECOS Stories TROPICAL STORMS IRENE AND LEE – A 0NE-TWO PUNCH TO THE HUDSON VALLEY

TROPICAL STORMS IRENE AND LEE – A 0NE-TWO PUNCH TO THE HUDSON VALLEY

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Prepared by Dennis Suszkowski, Hudson River Foundation, Sept. 19, 2011    

Tropical Storm Lee added a second punch to the Hudson Valley by dumping nearly as much rain as Irene. 

The HRECOS (Hudson River Environmental Conditions Observing System) network again provided a unique opportunity to evaluate impacts to the Hudson River from the combined storms.

The rainfall that preceded Irene, combined with the rain from both storms, saturated watershed soils, eroded stream banks, and sent unprecedented amounts of water and sediment into tributary streams which rapidly entered the Hudson River.  Figure 1 shows rainfall amounts caught in HRECOS gauges at Tivoli Bays and Albany.  Midhudsonweather.com reports that both storms combined to drop between 9 and 18 inches of rain within the Valley.   Figure 2 shows the accelerating discharge of water in Schoharie Creek, a tributary to the Mohawk River, preceding and during the two storms.  The discharge during Irene was likely three orders of magnitude (1,000X) the average discharge of the creek.   

Figure 1 

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Like Irene on August 30th, Lee was able to inject enough water into the Hudson such that the river on September 10th was “fresh” through its entire length.  This can be seen at the HRECOS station at Castle Point, offshore of Hoboken, NJ (Figure3).

Figure 2

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Figure 3

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At the northern end of the Hudson Estuary, Lee also overwhelmed the tides at the Albany and Schodack Island HRECOS stations, but to a lesser degree than Irene, as shown in Figure 4.

Figure  4 

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While the peak discharges for Irene were generally greater (in the Hudson and its tributaries ) than Lee, Lee pounded the Hudson Valley for a longer period of time and may have contributed greater quantities of water to the Hudson because of the saturated soil conditions that enhanced runoff  in most parts of the watershed.  This can be seen as the wider peak associated with Lee in Figure 5, discharge at the USGS gauging station at Green Island, just north of the Troy Dam.

Figure 5 

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As discussed in an earlier report about the impacts of Irene, the added sediment load to Hudson from Irene is thought to be significantly large.  With the addition of Lee, that load may have more than doubled to a gross estimate of 600,000 tons of sediments.  This could equate to a volume of more than 2 million cubic yards of sediment, or roughly twice the amount of sediment dredged from New York Harbor each year. 

Sediment added to the river shows up as spikes in turbidity measurements at HRECOS stations.  Figure 6 shows turbidity levels rapidly increasing during Irene and Lee at Norrie Point and Schodack Island.  It is interesting to note that high turbidity levels at Norrie Point are persisting longer than at Schodack Island, presumably showing how sediment is moving downstream.

Figure 6 

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High turbidity levels in rivers and estuaries along the east coast, as a consequence of the storms, have been observed from orbiting space craft.   A dramatic image (Figure 7) of sediment pouring out of the Hudson into Upper Bay of New York Harbor was taken by the NASA EO-1 (Earth Observing – 1) Satellite on September 12, 2011.  Large quantities of sediment are visibly shown to be entering the harbor days after Lee had passed.

Figure 7 

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Figure 8 is a NASA image of the same area taken one year earlier (September 12, 2010).  The dark color indicates relatively minor amounts of sediment suspended in the water column.

Figure 8 

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Note:  All of the data used in this report are subject to revision.  Therefore, the conclusions presented here are to be considered preliminary.

Last Updated on Monday, 16 July 2012 19:07