The U.S. Army Corps of Engineers (USACE) and the Nature Conservancy developed the Sustainable Rivers Program (SRP) as a collaborative environmental flows program to identify, refine, and implement environmental strategies at select USACE dams. The SRP was introduced to the Willamette Basin, Oregon, in 2007 through a series of environmental flow workshops, which led to stakeholder generated environmental flow recommendations in the North Santiam, South Santiam, Santiam (Bach and others, 2013), McKenzie, South Fork McKenzie (Risley and others, 2010), and Middle Fork Willamette Rivers (Gregory and others, 2007, https://www.hec.usace.army.mil/sustainablerivers/). This data release is a compilation of the stakeholder-defined environmental flow recommendations paired with flow data at the corresponding U.S. Geological Survey (USGS) streamflow gaging stations for each water-year spanning 2008 through 2022.

This tabular data set represents base flow index (BFI) compiled for two spatial components of the NHDPlus version 2 data suite (NHDPlusv2) for the conterminous United States; 1) individual reach catchments and 2) reach catchments accumulated upstream through the river network. This dataset can be linked to the NHDPlus version 2 data suite by the unique identifier COMID. The source data is the "Base-flow index grid for the conterminous United States" produced by the United States Geological Survey (Wolock, 2003). Units are percent. Base flow is the component of streamflow that can be attributed to ground-water discharge into streams. The BFI is the ratio of base flow to total flow, expressed as a percentage. Reach catchment information characterizes data at the local scale. Reach catchments accumulated upstream through the river network characterizes cumulative upstream conditions. Network-accumulated values are computed using two methods, 1) divergence-routed and 2) total cumulative drainage area. Both approaches use a modified routing database to navigate the NHDPlus reach network to aggregate (accumulate) the metrics derived from the reach catchment scale. (Schwarz and Wieczorek, 2018).

This tabular data set represents base flow index (BFI) compiled for two spatial components of the NHDPlus version 2 data suite (NHDPlusv2) for the conterminous United States; 1) individual reach catchments and 2) reach catchments accumulated upstream through the river network. This dataset can be linked to the NHDPlus version 2 data suite by the unique identifier COMID. The source data is the "Base-flow index grid for the conterminous United States" produced by the United States Geological Survey (Wolock, 2003). Units are percent. Base flow is the component of streamflow that can be attributed to ground-water discharge into streams. The BFI is the ratio of base flow to total flow, expressed as a percentage. Reach catchment information characterizes data at the local scale. Reach catchments accumulated upstream through the river network characterizes cumulative upstream conditions. Network-accumulated values are computed using two methods, 1) divergence-routed and 2) total cumulative drainage area. Both approaches use a modified routing database to navigate the NHDPlus reach network to aggregate (accumulate) the metrics derived from the reach catchment scale. (Schwarz and Wieczorek, 2018).

The Water Availability Tool for Environmental Resources (WATER-KY; Williamson and others, 2009) provides the ability to simulate streamflow for ungaged basins. This model integrates TOPMODEL (Beven and Kirkby, 1979) for pervious portions of the landscape with simulation of flow generated from impervious surfaces (USDA, 1986). A restructured version of this decision support tool translates the abilities of WATER to a format that can be used without proprietary software (Williamson and others, 2021). Additional functionality has also been added to include hydrologic response units (HRUs) that are defined based on three fundamental land-use categories: forest, agricultural land, and developed areas, based on subsequent development of WATER for the Delaware River Basin (Williamson and others, 2015). This refinement for agricultural areas, combined with the new software environment that enables easy substitution of precipitation and temperature data was used to develop a method focused on recent conditions in order to simulate daily peak streamflow for forecasted precipitation totals as well as the associated stage in order to identify if flood conditions are possible. Beven, K.J., and Kirkby, M.J., 1979, A physically based, variable contributing area model of basin hydrology / Un modèle à base physique de zone d'appel variable de l'hydrologie du bassin versant: Hydrological Sciences Bulletin v. 24, p. 43-69, https://doi.org/10.1080/02626667909491834. U.S. Department of Agriculture [USDA], 1986, Urban hydrology for small watersheds: Natural Resources Conservation Service, Conservation Engineering Division, Technical Release 55, Revised June 1986, Update of Appendix A January 1999, https://www.nrc.gov/docs/ML1421/ML14219A437.pdf. Williamson, T.N., Hoefling, D.J., Headman, A.O., and Gerzan, M.N., 2021, Water Availability Tool for Environmental Resources for the Commonwealth of Kentucky updated for 2019: U.S. Geological Survey data release, https://doi.org/10.5066/P9AQH027. Williamson, T.N., Lant, J.G., Claggett, P.R., Nystrom, E.A., Milly, P.C.D., Nelson, H.L., Hoffman, S.A., Colarullo, S.J., and Fischer, J.M., 2015, Summary of hydrologic modeling for the Delaware River Basin using the Water Availability Tool for Environmental Resources (WATER): U.S. Geological Survey Scientific Investigations Report 2015–5143, 68 p., https://doi.org/10.3133/sir20155143. Williamson, T.N., Odom, K.R., Newson, J.K., Downs, A.C., Nelson Jr., H.L., Cinotto, P.J., and Ayers, M.A., 2009, The Water Availability Tool for Environmental Resources (WATER)—A water-budget modeling approach for managing water-supply resources in Kentucky—Phase I—Data processing, model development, and application to non-karst areas:U.S. Geological Survey Scientific Investigations Report 2009–5248, 34 p., https://doi.org/10.3133/sir20095248.

The Water Availability Tool for Environmental Resources (WATER-KY; Williamson and others, 2009) provides the ability to simulate streamflow for ungaged basins. This model integrates TOPMODEL (Beven and Kirkby, 1979) for pervious portions of the landscape with simulation of flow generated from impervious surfaces (USDA, 1986). A restructured version of this decision support tool translates the abilities of WATER to a format that can be used without proprietary software (Williamson and others, 2021). Additional functionality has also been added to include hydrologic response units (HRUs) that are defined based on three fundamental land-use categories: forest, agricultural land, and developed areas, based on subsequent development of WATER for the Delaware River Basin (Williamson and others, 2015). This refinement for agricultural areas, combined with the new software environment that enables easy substitution of precipitation and temperature data was used to develop a method focused on recent conditions in order to simulate daily peak streamflow for forecasted precipitation totals as well as the associated stage in order to identify if flood conditions are possible. Beven, K.J., and Kirkby, M.J., 1979, A physically based, variable contributing area model of basin hydrology / Un modèle à base physique de zone d'appel variable de l'hydrologie du bassin versant: Hydrological Sciences Bulletin v. 24, p. 43-69, https://doi.org/10.1080/02626667909491834. U.S. Department of Agriculture [USDA], 1986, Urban hydrology for small watersheds: Natural Resources Conservation Service, Conservation Engineering Division, Technical Release 55, Revised June 1986, Update of Appendix A January 1999, https://www.nrc.gov/docs/ML1421/ML14219A437.pdf. Williamson, T.N., Hoefling, D.J., Headman, A.O., and Gerzan, M.N., 2021, Water Availability Tool for Environmental Resources for the Commonwealth of Kentucky updated for 2019: U.S. Geological Survey data release, https://doi.org/10.5066/P9AQH027. Williamson, T.N., Lant, J.G., Claggett, P.R., Nystrom, E.A., Milly, P.C.D., Nelson, H.L., Hoffman, S.A., Colarullo, S.J., and Fischer, J.M., 2015, Summary of hydrologic modeling for the Delaware River Basin using the Water Availability Tool for Environmental Resources (WATER): U.S. Geological Survey Scientific Investigations Report 2015–5143, 68 p., https://doi.org/10.3133/sir20155143. Williamson, T.N., Odom, K.R., Newson, J.K., Downs, A.C., Nelson Jr., H.L., Cinotto, P.J., and Ayers, M.A., 2009, The Water Availability Tool for Environmental Resources (WATER)—A water-budget modeling approach for managing water-supply resources in Kentucky—Phase I—Data processing, model development, and application to non-karst areas:U.S. Geological Survey Scientific Investigations Report 2009–5248, 34 p., https://doi.org/10.3133/sir20095248.

Nonstationary streamflow due to environmental and human-induced causes can affect water quality over time, yet these effects are poorly accounted for in water-quality trend models. This data release provides instream water-quality trends and estimates of two components of change, for sites across the Nation previously presented in Oelsner et al. (2017). We used previously calibrated Weighted Regressions on Time, Discharge, and Season (WRTDS) models published in De Cicco et al. (2017) to estimate instream water-quality trends and associated uncertainties with the generalized flow normalization procedure available in EGRET version 3.0 (Hirsch et al., 2018a) and EGRETci version 2.0 (Hirsch et al., 2018b). The procedure allows for nonstationarity in the flow regime, whereas previous versions of EGRET assumed streamflow stationarity. Water-quality trends of annual mean concentrations and loads (also referred to as fluxes) are provided as an annual series and the change between the start and end year for four trend periods (1972-2012, 1982-2012, 1992-2012, and 2002-2012). Information about the sites, including the collecting agency and associated streamflow gage, and information about site selection and the data screening process can be found in Oelsner et al. (2017). This data release includes results for 19 water-quality parameters including nutrients (ammonia, nitrate, filtered and unfiltered orthophosphate, total nitrogen, total phosphorus), major ions (calcium, chloride, magnesium, potassium, sodium, sulfate), salinity indicators (specific conductance, total dissolved solids), carbon (alkalinity, dissolved organic carbon, total organic carbon), and sediment (total suspended solids, suspended-sediment concentration) at over 1,200 sites. Note, the number of parameters with data varies by site with most sites having data for 1-4 parameters. Each water-quality trend was parsed into two components of change: (1) the streamflow trend component (QTC) and (2) the watershed management trend component (MTC). The QTC is an indicator of the amount of change in the water-quality trend attributed to changes in the streamflow regime, and the MTC is an indicator of the amount of change in the water-quality trend that may be attributed to human actions and changes in point and non-point sources in a watershed. Note, the MTC is referred to as the concentration-discharge trend component (CQTC) in the EGRET version 3.0 software. For our work, we chose to refer to this trend component as the MTC because it provides a more conceptual description (Murphy and Sprague, 2019). The trend results presented here expand upon the results in De Cicco et al. (2017) and Oelsner et al. (2017), which were analyzed using flow-normalization under the stationary streamflow assumption. The results presented in this data release are intended to complement these previously published results and support investigations into natural and human effects on water-quality trends across the United States. Data preparation information and WRTDS model specifications are described in Oelsner et al. (2017) and Murphy and Sprague (2019). This work was completed as part of the National Water-Quality Assessment (NAWQA) project of the National Water-Quality Program. De Cicco, L.A., Sprague, L.A., Murphy, J.C., Riskin, M.L., Falcone, J.A., Stets, E.G., Oelsner, G.P., and Johnson, H.M., 2017, Water-quality and streamflow datasets used in the Weighted Regressions on Time, Discharge, and Season (WRTDS) models to determine trends in the Nation’s rivers and streams, 1972-2012 (ver. 1.1 July 7, 2017): U.S. Geological Survey data release, https://doi.org/10.5066/F7KW5D4H. Hirsch, R., De Cicco, L., Watkins, D., Carr, L., and Murphy, J., 2018a, EGRET: Exploration and Graphics for RivEr Trends, version 3.0, https://CRAN.R-project.org/package=EGRET. Hirsch, R., De Cicco, L., and Murphy, J., 2018b, EGRETci: Exploration and Graphics for RivEr Trends (EGRET) Confidence Intervals, version 2.0.

Nonstationary streamflow due to environmental and human-induced causes can affect water quality over time, yet these effects are poorly accounted for in water-quality trend models. This data release provides instream water-quality trends and estimates of two components of change, for sites across the Nation previously presented in Oelsner et al. (2017). We used previously calibrated Weighted Regressions on Time, Discharge, and Season (WRTDS) models published in De Cicco et al. (2017) to estimate instream water-quality trends and associated uncertainties with the generalized flow normalization procedure available in EGRET version 3.0 (Hirsch et al., 2018a) and EGRETci version 2.0 (Hirsch et al., 2018b). The procedure allows for nonstationarity in the flow regime, whereas previous versions of EGRET assumed streamflow stationarity. Water-quality trends of annual mean concentrations and loads (also referred to as fluxes) are provided as an annual series and the change between the start and end year for four trend periods (1972-2012, 1982-2012, 1992-2012, and 2002-2012). Information about the sites, including the collecting agency and associated streamflow gage, and information about site selection and the data screening process can be found in Oelsner et al. (2017). This data release includes results for 19 water-quality parameters including nutrients (ammonia, nitrate, filtered and unfiltered orthophosphate, total nitrogen, total phosphorus), major ions (calcium, chloride, magnesium, potassium, sodium, sulfate), salinity indicators (specific conductance, total dissolved solids), carbon (alkalinity, dissolved organic carbon, total organic carbon), and sediment (total suspended solids, suspended-sediment concentration) at over 1,200 sites. Note, the number of parameters with data varies by site with most sites having data for 1-4 parameters. Each water-quality trend was parsed into two components of change: (1) the streamflow trend component (QTC) and (2) the watershed management trend component (MTC). The QTC is an indicator of the amount of change in the water-quality trend attributed to changes in the streamflow regime, and the MTC is an indicator of the amount of change in the water-quality trend that may be attributed to human actions and changes in point and non-point sources in a watershed. Note, the MTC is referred to as the concentration-discharge trend component (CQTC) in the EGRET version 3.0 software. For our work, we chose to refer to this trend component as the MTC because it provides a more conceptual description (Murphy and Sprague, 2019). The trend results presented here expand upon the results in De Cicco et al. (2017) and Oelsner et al. (2017), which were analyzed using flow-normalization under the stationary streamflow assumption. The results presented in this data release are intended to complement these previously published results and support investigations into natural and human effects on water-quality trends across the United States. Data preparation information and WRTDS model specifications are described in Oelsner et al. (2017) and Murphy and Sprague (2019). This work was completed as part of the National Water-Quality Assessment (NAWQA) project of the National Water-Quality Program. De Cicco, L.A., Sprague, L.A., Murphy, J.C., Riskin, M.L., Falcone, J.A., Stets, E.G., Oelsner, G.P., and Johnson, H.M., 2017, Water-quality and streamflow datasets used in the Weighted Regressions on Time, Discharge, and Season (WRTDS) models to determine trends in the Nation’s rivers and streams, 1972-2012 (ver. 1.1 July 7, 2017): U.S. Geological Survey data release, https://doi.org/10.5066/F7KW5D4H. Hirsch, R., De Cicco, L., Watkins, D., Carr, L., and Murphy, J., 2018a, EGRET: Exploration and Graphics for RivEr Trends, version 3.0, https://CRAN.R-project.org/package=EGRET. Hirsch, R., De Cicco, L., and Murphy, J., 2018b, EGRETci: Exploration and Graphics for RivEr Trends (EGRET) Confidence Intervals, version 2.0.

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.