This Child Item contains (1) a table of trends in eight annual streamflow statistics for the time periods 1940-1969, 1970-1999, and 2000-2018, and (2) a .zip file of plots of the eight statistical trends for the three time periods. The annual streamflow statistics and their trends were computed by Climate Year (CY) for 1-,7- and 30-day minima and by Water Year (WY) for 1-,7- and 30-day maxima, median and mean. Streamgages from the original dataset (n = 409) were excluded from one or more time periods of analysis because of extensive data gaps that would interrupt trend lines; therefore, streamgages were indexed into the earliest possible time period relative to their installation date (for example, a streamgage with an operating start year of 1958 would be included in the analysis for the time periods 1970-1999 and 2000-2018), which resulted in different sample sizes for each period: 1940-1969 (n = 90), 1970-1999 (n = 167), and 2000-2018 (n = 243). Similarly, multiple streamgages were wholly excluded because of frequent discontinuities in the daily mean streamflow used to derive the annual mean streamflow through all three time periods.

Ecological flow (EFlow) statistics have been designated to characterize the magnitude, frequency, and duration of extreme high- and low-flows, the timing of seasonal flows, and the consistency of the historic regime. This Child Item contains a table of 178 EFlows for the time periods 1940-1969, 1970-1999, and 2000-2018, with absolute and percent change between periods, where applicable. Statistics were computed by Water Year (WY) for all 178 metrics and absolute and percent change were calculated by comparing metrics between combinations of two of the three time periods (1940-1969 and 1970-1999; 1940-1969 and 2000-2018; 1970-1999 and 2000-2018). Streamgages from the original dataset (n = 409) were excluded from one or more time periods of analysis because of extensive data gaps that would yield incomplete EFlows; therefore, stations were indexed into the earliest possible time period relative to their installation date (for example, a streamgage with an operating start year of 1958 would be included in the analysis for the time periods 1970-1999 and 2000-2018), which resulted in different sample sizes for each period: 1940-1969 (n = 90), 1970-1999 (n = 167), and 2000-2018 (n = 243). Similarly, multiple stations were wholly excluded because of frequent discontinuities in the daily mean streamflow through all three time periods. Finally, a streamgage must have fallen within at least two time periods to have a change value. As such, not all stations are represented in the change analysis (change between 1940-1969 and 1970-1999 [n = 90]; change between 1940-1969 and 2000-2018 [n = 90]; change between 1970-1999 and 2000-2018 [n = 167]).

Ecological flow (EFlow) statistics have been designated to characterize the magnitude, frequency, and duration of extreme high- and low-flows, the timing of seasonal flows, and the consistency of the historic regime. This Child Item contains a table of 178 EFlows for the time periods 1940-1969, 1970-1999, and 2000-2018, with absolute and percent change between periods, where applicable. Statistics were computed by Water Year (WY) for all 178 metrics and absolute and percent change were calculated by comparing metrics between combinations of two of the three time periods (1940-1969 and 1970-1999; 1940-1969 and 2000-2018; 1970-1999 and 2000-2018). Streamgages from the original dataset (n = 409) were excluded from one or more time periods of analysis because of extensive data gaps that would yield incomplete EFlows; therefore, stations were indexed into the earliest possible time period relative to their installation date (for example, a streamgage with an operating start year of 1958 would be included in the analysis for the time periods 1970-1999 and 2000-2018), which resulted in different sample sizes for each period: 1940-1969 (n = 90), 1970-1999 (n = 167), and 2000-2018 (n = 243). Similarly, multiple stations were wholly excluded because of frequent discontinuities in the daily mean streamflow through all three time periods. Finally, a streamgage must have fallen within at least two time periods to have a change value. As such, not all stations are represented in the change analysis (change between 1940-1969 and 1970-1999 [n = 90]; change between 1940-1969 and 2000-2018 [n = 90]; change between 1970-1999 and 2000-2018 [n = 167]).

The hydrologic regime of rivers and streams is a major determinant of habitat quality for fish and aquatic invertebrates. Long-term streamflow data were compiled and multidecadal streamflow trends and ecological flow (EFlow) statistics were calculated in support of the United States Geological Survey (USGS) Chesapeake Bay Science Initiative toward understanding fish habitat and health in the Chesapeake Bay Watershed (CBWS). A dataset comprising all streamgages (n = 409) reporting daily means of streamflow within the CBWS and remaining active as of September 30, 2018 (the end of Water Year [WY] 2018), independent of streamgage installation date, was retrieved from the USGS National Water Information System (NWIS). This dataset was then subset to include only those streamgages with a contiguous timeseries of streamflow data from a start date no earlier than April 1, 1939 (Climate Year [CY] 1940) and no later than October 1, 1999 (WY 2000). The R packages “EGRET” and "Eflowstats" were utilized together to determine streamflow trends and EFlow statistics from the subset (n = 243). Trends and EFlows were computed for the ranges 1940-1969 (n = 90), 1970-1999 (n = 167), and 2000-2018 (n = 243). Streamflow trends were computed for eight annual metrics (1-, 7- and 30-day minima [CY] and maxima [WY], mean and median [WYs]). These streamflow trends provide context for the 178 EFlow statistics (WY) which have been designated to characterize the magnitude, frequency, and duration of extreme high and low flows, the timing of seasonal flows, and the consistency of the historic regime. Files herein include the following Child Items: (1) a table summarizing streamflow trends for three time periods at a minimum of 90 and maximum of 243 streamgages and 500 time-series plots graphically representing those trends; (2) a table summarizing EFlow statistics and the change between each statistic for three time periods at a minimum of 90 and maximum of 243 streamgages; and (3) a GIS shapefile of the original 409 USGS streamgage locations, complete with NWIS attributes, active within the CBWS through September 30, 2018.

The hydrologic regime of rivers and streams is a major determinant of habitat quality for fish and aquatic invertebrates. Long-term streamflow data were compiled and multidecadal streamflow trends and ecological flow (EFlow) statistics were calculated in support of the United States Geological Survey (USGS) Chesapeake Bay Science Initiative toward understanding fish habitat and health in the Chesapeake Bay Watershed (CBWS). A dataset comprising all streamgages (n = 409) reporting daily means of streamflow within the CBWS and remaining active as of September 30, 2018 (the end of Water Year [WY] 2018), independent of streamgage installation date, was retrieved from the USGS National Water Information System (NWIS). This dataset was then subset to include only those streamgages with a contiguous timeseries of streamflow data from a start date no earlier than April 1, 1939 (Climate Year [CY] 1940) and no later than October 1, 1999 (WY 2000). The R packages “EGRET” and "Eflowstats" were utilized together to determine streamflow trends and EFlow statistics from the subset (n = 243). Trends and EFlows were computed for the ranges 1940-1969 (n = 90), 1970-1999 (n = 167), and 2000-2018 (n = 243). Streamflow trends were computed for eight annual metrics (1-, 7- and 30-day minima [CY] and maxima [WY], mean and median [WYs]). These streamflow trends provide context for the 178 EFlow statistics (WY) which have been designated to characterize the magnitude, frequency, and duration of extreme high and low flows, the timing of seasonal flows, and the consistency of the historic regime. Files herein include the following Child Items: (1) a table summarizing streamflow trends for three time periods at a minimum of 90 and maximum of 243 streamgages and 500 time-series plots graphically representing those trends; (2) a table summarizing EFlow statistics and the change between each statistic for three time periods at a minimum of 90 and maximum of 243 streamgages; and (3) a GIS shapefile of the original 409 USGS streamgage locations, complete with NWIS attributes, active within the CBWS through September 30, 2018.

This data set contains U.S. Geological Survey (USGS) streamgage identification numbers, begin and end years of the periods of streamflow record tested, Sen slope trends in the annual minimum 7-day streamflow for the period of record tested, the p-values (significance) of the trends, and the trend Sen slopes standardized by the standard deviations of the residual errors defined as the difference between observations and the Sen slope lines, for 174 USGS streamgages with 56 to 75 years of record in the Chesapeake Bay watershed, Mid-Atlantic U.S.

This data set contains U.S. Geological Survey (USGS) streamgage identification numbers, begin and end years of the periods of streamflow record tested, Sen slope trends in the annual minimum 7-day streamflow for the period of record tested, the p-values (significance) of the trends, and the trend Sen slopes standardized by the standard deviations of the residual errors defined as the difference between observations and the Sen slope lines, for 174 USGS streamgages with 56 to 75 years of record in the Chesapeake Bay watershed, Mid-Atlantic U.S.

This Child Item contains a shapefile (ArcGIS Pro version 2.5.0) of the original 409 USGS streamgage locations active within the Chesapeake Bay Watershed (CBWS) through September 30, 2018. Streamflow trends and EFlow statistics tables from this data release may be joined to the shapefile by either the "Streamgage_ID" or "Streamgage_Name" attributes to aid in spatial analysis within a GIS.

This Child Item contains a shapefile (ArcGIS Pro version 2.5.0) of the original 409 USGS streamgage locations active within the Chesapeake Bay Watershed (CBWS) through September 30, 2018. Streamflow trends and EFlow statistics tables from this data release may be joined to the shapefile by either the "Streamgage_ID" or "Streamgage_Name" attributes to aid in spatial analysis within a GIS.

This dataset contains statistical descriptions of observed daily-mean streamflow for 956 sites in the southeast United States. For each site, statistical descriptions are provided according to decade for up to six decades, beginning in 1950 (1950-59 calendar years) and ending with 2000 (2000 - 2009 calendar years) with no more than 7 missing values per year in total (continuous or noncontinuous). There are 40 statistical descriptions including 28 flow-duration curve values, 8 L-moments, and 4 describing the minimum, maximum, median flow for days not equal to zero, and number of zero-flow days. Site information is provided by decade - the number of rows per site varies from 1 to 6 depending on the number of decades with observed record available. This information was used as the response variable(s) for statistical models for estimating the same characteristics at nearly 10,000 ungaged locations throughout the southeast United States. The dataset has been provided as a shapefile and a comma-delimited file. The comma-delimited file is an exact copy of the attribute table of the shapefile.