1. River Flow into Chesapeake Bay
Normal Range
Wet Years
Dry
Years
Data and Methods:
Water Year Mean River Flow (billions of gallons per day)
Status: Total river flow to the Bay during the 2007 water year (October 2006-September 2007) was very close to the long-term average despite several months of extremes.
Additional Information:
About half the water in the Bay comes from the rivers, the other half from the ocean.
The U.S. Geological Survey, one of the Chesapeake Bay Program federal partners, has been monitoring the volume of freshwater flowing into the Bay – or river flow – from the three biggest rivers concurrently since 1937.
In an average year, three rivers deliver most (about 81%) of the river flow: Susquehanna (48%), Potomac (19%), and James (14%).
Annual Chesapeake Bay water quality conditions are largely determined by a combination of the amount of pollution deposited on the land or discharged in wastewater and the amount of water flowing into the Bay. As river flow increases, its potential to carry additional amounts of pollutants increases as well.
The Bay's watershed covers an enormous 64,000-square-mile area that includes parts of six states – Delaware, Maryland, New York, Pennsylvania, Virginia and West Virginia – and all of the District of Columbia. Billions of gallons of water flow each day through thousands of streams and rivers that eventually empty into the Bay. The Bay must process runoff from a large amount of land with a relatively small body of water.
Runoff from winter and spring rains deliver loads of sediment and nutrient pollutants to the Bay that drive summer water quality conditions in the Bay. Past observations reveal that summer weather conditions also contribute to summer water quality when intense storms increase erosion, which contributes to poor water clarity and adds to the existing nutrient load in the Bay.
Not all rain water “runs off” the land. Some water seeps into the soil, carrying nutrients into groundwater. The travel time of nutrients through the watershed ranges from weeks to centuries. This can result in a “lag time” between implementing management actions and improvements in water quality.
Chesapeake Bay Health and Restoration Assessment:
Factors Impacting Bay & Watershed Health
3/25/08