Freshwater Flow into Chesapeake Bay
Interactive Graphs of Monthly Mean Streamflow Entering Chesapeake Bay
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Explore resources here describing estimates of freshwater flow entering Chesapeake Bay.
The health of the Chesapeake Bay is greatly affected by freshwater flow from rivers draining its watershed. The amount of freshwater flow (also called streamflow) will:
• Change salinity levels in the Bay, which affect oysters, crabs, and finfish.
• Influence the amounts of nutrients, sediment, and contaminants delivered to tidal waters, which affects fisheries and submerged aquatic vegetation.
The USGS provides estimates of the monthly and annual amounts of freshwater flow into the Bay so scientists and managers can better understand effects on ecosystem conditions.
Monthly Mean Streamflow Over The Past 2 Years
Annual Mean Streamflow into the Chesapeake Bay
For more information
More detailed results describing estimated freshwater flow entering the Chesapeake Bay may be found on the results page.
Methods used to estimate freshwater flow are based on streamflow data from the Susquehanna, Potomac, and James Rivers, and may be found on the related science page. The data and tools page documents detailed results from each of these rivers.
Need answers to questions about Chesapeake Bay Estimated Streamflow technical issues? Contact Douglas L Moyer or Samuel H Austin.
For more information about USGS Chesapeake studies, contact Scott Phillips or Ken Hyer.
The results on this page include: (1) monthly flow to the Bay, (2) amount of flow from different watersheds, and (3) annual flow to the Bay. Summary statistics for each month are also provided.
Overview Recent Flow Activity Recent Flow Statistics Table Summary of Methods Website Programming History
Most recent estimated monthly mean streamflow entering Chesapeake Bay for February 2021 was 85,000 cubic feet per second. This value, (Figure 1, Line 1), which is provisional and subject to revision, is considered to be within the normal range of February streamflow. Normal streamflow entering the Bay in February is between 72,000 cubic feet per second (Figure 1, Line 3) and 130,000 cubic feet per second (Figure 1, Line 4), the 25th and 75th percentiles, respectively, of all February streamflow values over an 84-year period of record.
Recent Monthly Mean Streamflow Entering Chesapeake Bay
The Amount of Freshwater from Different Watersheds
The majority of freshwater flow enters the Bay from three major watersheds: Susquehanna, Potomac, and James (Figure 2). These three watersheds, and the remaining areas, are represented by five streamflow cross sections across the Bay (A through E; Figure 2). The amount of freshwater flow from these areas is estimated each month (figure 3).
In February 2021, the largest proportion of streamflow entered at Section D-E, accounting for about 31 percent of total streamflow entering the Bay. This information, along with proportional flow in recent months, is shown in Figure 3.
The Annual Freshwater Flow into the Chesapeake Bay
The estimated annual-mean streamflow entering the Chesapeake Bay over the period of record has been calculated for each of the complete water years in the period of record, beginning in 1937 as shown in Figure 4. For the most recent complete water year (2020), this value was 77,665 cubic feet per second. The long-term annual-mean streamflow is 79,000 cubic feet per second, and "normal" annual-mean streamflow is between 67,250 cubic feet per second and 88,750 cubic feet per second — the 25th and 75th percentiles of all annual-mean values, respectively. Of the most recent ten complete water years, six were normal, three were above normal, and one was below normal.
Learn more about Chesapeake Bay streamflow:
- View Chesapeake Bay recent monthly streamflow compared to historic conditions
- View Chesapeake Bay period-of-record summary statistics
- View and download Chesapeake Bay data for historic monthly and annual streamflow
- Read about Chesapeake Bay streamflow estimation methods
- Read about the 2019 water year record setting annual flow
A Table Listing Summary Statistics For The Past Two Years
Streamflow summary statistics for the past two years are listed below in tabular form. Streamflow summary statistics for the full period-of-record may be found HERE, under the Data and Tools tab. Streamflow codes are identified as follows: A, approved data; B, computed using only approved data; e, value involves manual editing by USGS personnel; L, computed using a summation of other values; M, computed using a model; N, computed using more than one model; P, provisional data; Q, computed using provisional data.
Year | Month | Date | Inflow Code | Estimated Inflow (cfs) | POR Mean | POR Minimum | POR 25th Percentile | POR 75th Percentile | POR Maximum |
---|---|---|---|---|---|---|---|---|---|
2021 | 2 | 2021-02 | PN | 85300 | 103000 | 36000 | 72000 | 130000 | 229000 |
2021 | 1 | 2021-01 | PN | 92800 | 91000 | 18000 | 57000 | 114000 | 246000 |
2020 | 12 | 2020-12 | PN | 134900 | 85000 | 17000 | 54000 | 106000 | 221000 |
2020 | 11 | 2020-11 | PN | 66800 | 62000 | 15000 | 32000 | 77000 | 212000 |
2020 | 10 | 2020-10 | PN | 32500 | 45000 | 10000 | 23000 | 52000 | 174000 |
2020 | 9 | 2020-09 | PN | 32200 | 38000 | 9000 | 17000 | 36000 | 201000 |
2020 | 8 | 2020-08 | PN | 38700 | 34000 | 10000 | 20000 | 40000 | 133000 |
2020 | 7 | 2020-07 | PN | 27100 | 40000 | 11000 | 25000 | 46000 | 121000 |
2020 | 6 | 2020-06 | PN | 67200 | 65000 | 18000 | 42000 | 76000 | 343000 |
2020 | 5 | 2020-05 | PN | 148200 | 101000 | 33000 | 62000 | 131000 | 217000 |
2020 | 4 | 2020-04 | PN | 125900 | 142000 | 56000 | 97000 | 175000 | 390000 |
2020 | 3 | 2020-03 | PN | 103100 | 144000 | 52000 | 103000 | 178000 | 299000 |
2020 | 2 | 2020-02 | PN | 117600 | 103000 | 36000 | 72000 | 130000 | 229000 |
2020 | 1 | 2020-01 | PN | 96100 | 91000 | 18000 | 57000 | 117000 | 246000 |
2019 | 12 | 2019-12 | PN | 76800 | 85000 | 17000 | 54000 | 106000 | 221000 |
2019 | 11 | 2019-11 | PN | 68300 | 62000 | 15000 | 32000 | 77000 | 212000 |
2019 | 10 | 2019-10 | PN | 32600 | 45000 | 10000 | 23000 | 52000 | 174000 |
2019 | 9 | 2019-09 | PN | 20700 | 38000 | 9000 | 17000 | 36000 | 201000 |
2019 | 8 | 2019-08 | PN | 32100 | 34000 | 10000 | 20000 | 40000 | 133000 |
2019 | 7 | 2019-07 | PN | 53800 | 40000 | 11000 | 25000 | 46000 | 121000 |
2019 | 6 | 2019-06 | PN | 95400 | 65000 | 18000 | 42000 | 76000 | 343000 |
2019 | 5 | 2019-05 | PN | 146700 | 101000 | 33000 | 62000 | 131000 | 217000 |
2019 | 4 | 2019-04 | PN | 154200 | 142000 | 56000 | 97000 | 175000 | 390000 |
2019 | 3 | 2019-03 | AN | 159600 | 144000 | 52000 | 103000 | 178000 | 299000 |
2019 | 2 | 2019-02 | AN | 176200 | 103000 | 36000 | 72000 | 130000 | 229000 |