The higher river flows following Hurricane Sandy will bring an increased amount of nutrient and sediment to the Chesapeake Bay; however these amounts will not approach the nutrient and sediment loads seen in 2011 from Hurricane Irene and Tropical Storm Lee, according to preliminary data released by the U.S. Geological Survey.
Flows in the Susquehanna River, the largest river entering the Chesapeake Bay, are expected to reach 155,000 cubic feet per second (cfs). This is much lower than last year’s flow of more than 775,000 cfs following Irene and Lee. The flow in the Susquehanna River due to Sandy is not expected to produce significant scour of sediments from the Conowingo Reservoir. The record was 1.1 million cfs during Hurricane Agnes in 1972.
Hurricane Sandy had a larger effect on the Potomac River watershed and Eastern Shore. Current flow at Little Falls in Washington, DC is 137,000 cfs and is near its expected peak. Current flow from the Potomac River is comparable to the Susquehanna River, even though the Potomac watershed is only half the size. The record for the Potomac is 484,000 cfs, set in 1936.
The Choptank River reached a peak of 4480 cfs, which was half of the flow seen during Irene or Lee.
Tracking river flow into the Chesapeake is important for the health of the bay. Too many nutrients rob the bay of oxygen needed for fish and, along with sediment, cloud the waters, disturbing the habitat of underwater plants crucial for aquatic life and waterfowl. However, according to the Chesapeake Bay Program, the impacts are not as great during this time of year compared to the summer months.
"Maximum river flows and associated sediment and pollutant loads from extreme storms are complicated functions of the amount and duration of the rainfall, the prior degree of ground saturation, the percentage of the total drainage basin affected, and the state of ground cover, among other factors," said USGS Director Marcia McNutt. "We are simply grateful for the health of the Chesapeake that Sandy didn't follow Irene's example!"
The USGS and partners are collecting samples of nutrients and sediment at the Chesapeake Bay Program Nontidal Water-Quality Network, which includes 125 sites. The results will be used to assess effects on the Bay and its watershed.
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