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Estimated Streamflow Entering Chesapeake Bay

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Estimated streamflow entering the Chesapeake Bay is computed on a monthly and annual basis using streamflow measurements from the Susquehanna, Potomac, and James Rivers. Data are presented in tables and graphs, typically grouped by water year — the natural, annual water cycle from October through September used by hydrologists.

The health of the Chesapeake Bay largely is driven by changes in streamflow and the amount of pollution it contains. Runoff in the Chesapeake Bay watershed carries pollutants, such as nutrients and sediments, to rivers and streams that drain to the Bay. Scientists can use estimated streamflow entering the Chesapeake Bay to assess the health of the Bay and make ecological forecasts.

In addition to this summary page, additional content is available:

Summary of Recent Streamflow Conditions, November 2018

The estimated monthly mean streamflow entering Chesapeake Bay for November 2018 was 215000 cubic feet per second (cfs). This value, which is provisional and subject to revision, is considered to be in the above normal range (Figure 1). Normal November streamflow entering the Bay is between 31100 and 78900 cfs, the 25th and 75th percentiles, respectively, of all November values. Average (mean) monthly streamflow for November is 60400 cfs. These statistics are based on a 82-year period of record.

Figure 1. Estimated monthly mean streamflow entering Chesapeake Bay for the current and previous water year. (more...).

Streamflow enters the Bay from many watersheds, and five cross sections across the Bay (A through E; Figure 2) can be used to better understand what proportion of streamflow comes from what watersheds. In November 2018, the largest proportion of streamflow entered at Section A, accounting for about 50 percent of total streamflow entering the Bay. This information, along with proportional flow in recent months, is shown in Figure 3.

Figure 2. Map of the drainage area of the Chesapeake Bay showing five cross sections across the Bay. Incremental streamflow entering the Bay between these cross sections is shown in Figure 3.

Figure 3. Estimated monthly mean streamflow entering Chesapeake Bay, shown proportionally by cross sections A-E. Water passing section A largely is from the Susquehanna River watershed; water entering between sections B and C largely is from the Potomac River watershed; and water entering between sections D and E largely is from the James River watershed. (more...).

Annual-Mean Streamflow Over the Period of Record

Estimated annual-mean streamflow entering the Chesapeake Bay has been calculated for each of the 82 complete years in the period of record, beginning in 1937 (Figure 4). For the most recent complete water year (2018), this value was 108000 cfs. The long-term annual-mean streamflow is 78800 cfs, and "normal" streamflow is between 67500 and 89800 cfs — the 25th and 75th percentiles of all annual-mean values, respectively. Of the most recent 10 complete water years, six were normal, two were above normal, and two were below normal.

Figure 4. Estimated annual-mean streamflow entering the Chesapeake Bay. The normal band (white), represents flow values between the 25th and 75th percentiles. Bars are shaded with respect to this normal band: blue for above normal, red for below normal, and gray for normal. (more...)

More Information

collage of Bay photos

Much more information about USGS Chesapeake Bay studies and activites can be found here.

This website would not be possible without long, uninterrupted records of streamflow data made possible by funding through partnerships between federal, state, and local agencies, and the USGS National Streamflow Information Program.

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Page Last Modified: Tuesday, February 19, 2019