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River Flow Into Chesapeake Bay

During the 2014 water year (October 2013 to September 2014), river flow to the Chesapeake Bay averaged 53 billion gallons per day. This is close to the long-term average of 51 billion gallons per day.


Each day, billions of gallons of fresh water flow from rivers and streams into the Chesapeake Bay. The amount of water flowing from these tributaries into the Bay has a direct impact on pollution: as snowmelt or rainfall increase river flow, more nutrients and sediment are pushed into the estuary. In other words, precipitation and river flow are factors affecting nitrogen, phosphorus and sediment loads and water quality.

Long-term trend (1937-2014)

Between 1937 and 2014, annual river flow to the Chesapeake Bay has averaged 50.9 billion gallons per day. While it has ranged from 29.3 to 78.2 billion gallons per day, the normal range of flow for this time is between 43.6 and 57.7 billion gallons per day.

Analyses from the U.S. Geological Survey (USGS) indicate normal river flow prior to 1960, a dry period during the 1960s and wetter conditions in the 1970s. Since 1990, river flow has been extremely variable.

Short-term trend (2004-2014)

The last decade has seen highly variable river flow. Water year 2004 was wet but was followed by four years of relatively normal flow. Water year 2009 was dry; 2010 was relatively normal; and 2011 was wet. Indeed, 2011 was one of the five wettest years on record due to a wet spring and a late summer and early fall hurricane and tropical storm. Water year 2012, 2013 and 2014 were relatively normal.

Change from previous year (2013-2014)

Between 2013 and 2014, average river flow increased from 49.12 to 52.54 billion gallons per day.

Additional Information

About half of the water in the Chesapeake Bay comes from its rivers and streams; the rest comes from the Atlantic Ocean. In an average year, three rivers deliver most (about 81 percent) of the river flow to the Bay: the Susquehanna (48 percent), the Potomac (19 percent) and the James (14 percent).

The U.S. Geological Survey (USGS) uses monitoring data from the Susquehanna, Potomac and James to estimate river flow to the Bay. The USGS updates flow each month and compiles a summary each year. Trend analyses are available in USGS Circular 1316, Chapter 5 and in a more recent report assessing trends between 1985 and 2010.

Source of Data

US Geological Survey

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