This dataset contains four tables: (1) site, regression and weighted peak flow estimates (peak_flow_estimates.csv) (2) site, regression and weighted low flow estimates (low_flow_estimates.csv) (3) basin characteristics for peak flow sites (peak_basin_stats.csv) (4) basin characteristics for low flow sites (low_basin_stats.csv). These tables support the USGS report "Magnitude and Frequency of Peak Flows and Low Flows on Nontidal Streams in Delaware."

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 dataset contains annual metrics quantifying low streamflows, climate, topography, land cover and geology for 325 USGS GAGES-2 watersheds within the Delaware River Basin boundary or with watershed centroids within a 25-mile buffer of the Delaware River Basin boundary.

Estimates of various low-flow statistics were computed at 71 ungaged stream locations throughout New Jersey during the 2017 water year using methods in the published reports, Streamflow Characteristics and Trends in New Jersey, Water Years 1897-2003 (U.S. Geological Survey Scientific Investigations Report 2005-5105) and Implementation of MOVE.1, Censored MOVE.1, and Piecewise MOVE.1 Low-Flow Regressions With Applications at Partial-Record Streamgages in New Jersey (U.S. Geological Survey Open File Report 2018-1089). The estimates are computed as needed for use in water resources permitting, assessment, and management by the New Jersey Department of Environmental Protection. The data release includes the stream name, location, method of estimation, drainage area, and intended use of the low-flow statistics computed during the 2017 water year. The data are provided as both a plain text file and ArcGIS shapefile format.

This U.S. Geological Survey (USGS) data release contains estimated daily streamflow and base flow for HUC12 in the nontidal areas of the Chesapeake Bay watershed, monthly average streamflow and base flow, flow statistics, MATLAB scripts, and a document that describes how to create similar datasets in other watersheds. Daily streamflow was estimated for all the nontidal parts of the Chesapeake Bay watershed with the program "Unit Flows in Networks of Channels" (UFINCH; Holtschlag, 2016), together with the observations of measured streamflow at gages at the downstream ends of major rivers. The estimated streamflow was aggregated at the HUC12 level and reformatted as an Optimal Hydrograph Separation (OHS) input file using MATLAB scripts. Base flow was calculated at each HUC12 outlet using the base flow index (BFI) hydrograph separation methods developed by Wahl and Wahl (Wahl and Wahl, 1988; Wahl and Wahl, 1995) and by Eckhardt (Eckhardt, 2005) with the parameter estimation method developed by Collischonn and Fan (Collischonn and Fan, 2013) which are incorporated into the OHS program (Raffensperger and others, 2017). This data release supports the following publication: • Buffington, P.C., and Capel, P.D., 2020, Estimating streamflow and base flow within the nontidal Chesapeake Bay riverine system: U.S. Geological Survey Scientific Investigations Report 2020-5055, 26 p., https://doi.org/10.3133/sir20205055. References cited: • Collischonn, W. and Fan, F.M., 2013, Defining parameters for Eckhardt's digital baseflow filter: Hydrological Processes, v. 27, no. 18, p. 2614-2622, https://doi.org/10.1002/hyp.9391. • Eckhardt, K., 2005, How to construct recursive digital filters for baseflow separation: Hydrological Processes, v. 19, no. 2, p. 507-515, https://doi.org/10.1002/hyp.5675. • Holtschlag, D.J., 2016, UFINCH-A method for simulating unit and daily flows in networks of channels described by NHDPlus using continuous flow data at U.S. Geological Survey streamgages: U.S. Geological Survey Scientific Investigations Report 2016-5074, 17 p., https://doi.org/10.3133/sir20165074. • Raffensperger, J.P., Baker, A.C., Blomquist, J.D., and Hopple, J.A., 2017, Optimal hydrograph separation using a recursive digital filter constrained by chemical mass balance, with application to selected Chesapeake Bay watersheds: U.S. Geological Survey Scientific Investigations Report 2017-5034, 51 p., https://doi.org/10.3133/sir20175034. • Wahl, K.L., and Wahl, T.L., 1988, Effects of regional ground water declines on streamflows in the Oklahoma Panhandle, in Symposium on Water-Use Data for Water Resources Management, Tucson, Arizona, American Water Resources Association, p. 239-249. • Wahl, K.L., and Wahl, T.L., 1995, Determining the flow of Comal Springs at New Braunfels, Texas, Texas Water '95: San Antonio, Texas, American Society of Civil Engineers, p. 77-86, http://www.usbr.gov/tsc/techreferences/hydraulics_lab/pubs/PAP/PAP-0708.pdf.

The U.S. Geological Survey (USGS) operates a dense network of streamgages within the Delaware River Basin (DRB) that provides near real-time and daily mean streamflow values, many of which have a decades long period of record. This long-term, historical dataset of daily mean streamflows is crucial for prediction of flows at ungaged stream reaches by means of parameter-based regression equations and can assist in informing water management and use decisions within the DRB. The USGS computed updated flow-duration exceedance probabilities for 98 current (2022) reference streamgages within the DRB with at least 10 years of record and minimally altered (nominal anthropogenic activity such as mining, diversion, or impoundment) streamflow regimes. The Make Plotting Position (MkPP; Granato, 2009) program with Weibull plotting position was used to calculate flow-duration exceedance probabilities for 21 streamflow percentiles. Percent difference comparison between these resulting flow-duration exceedances were made with observed and regression equation predicted streamflow values published by Stuckey (2016) for the 1960 through 2010 time period. A time-series trend analysis of 1979–2022 daily mean streamflows at 19 percentiles was computed using a non-parametric Mann-Kendall trend test (Hirsch and others, 2015). Associated basin characteristic raster layers that are currently used in StreamStats for the DRB, including percentage sand in soil, percentage poorly drained soils, percentage urban land use, mean annual precipitation, mean winter precipitation (December–February), and soil hydraulic conductivity, are included in this data release. Citations: Granato, G.E., 2009, Computer programs for obtaining and analyzing daily mean streamflow data from the U.S. Geological Survey National Water Information System Web Site: U.S. Geological Survey Open-File Report 2008–1362, 123 p. on CD-ROM, 5 appendixes, https://pubs.usgs.gov/publication/ofr20081362 Hirsch R.M., DeCicco L.A., 2015, User Guide to Exploration and Graphics for RivEr Trends (EGRET) and dataRetrieval: R Packages for Hydrologic Data: U.S. Geological Survey Techniques and Methods 4-A10, https://pubs.usgs.gov/tm/04/a10/ Stuckey, M.H., 2016, Estimation of daily mean streamflow for ungaged stream locations in the Delaware River Basin, water years 1960–2010: U.S. Geological Survey Scientific Investigations Report 2015–5157, 42 p., http://dx.doi.org/10.3133/sir20155157

The U.S. Geological Survey (USGS) operates a dense network of streamgages within the Delaware River Basin (DRB) that provides near real-time and daily mean streamflow values, many of which have a decades long period of record. This long-term, historical dataset of daily mean streamflows is crucial for prediction of flows at ungaged stream reaches by means of parameter-based regression equations and can assist in informing water management and use decisions within the DRB. The USGS computed updated flow-duration exceedance probabilities for 98 current (2022) reference streamgages within the DRB with at least 10 years of record and minimally altered (nominal anthropogenic activity such as mining, diversion, or impoundment) streamflow regimes. The Make Plotting Position (MkPP; Granato, 2009) program with Weibull plotting position was used to calculate flow-duration exceedance probabilities for 21 streamflow percentiles. Percent difference comparison between these resulting flow-duration exceedances were made with observed and regression equation predicted streamflow values published by Stuckey (2016) for the 1960 through 2010 time period. A time-series trend analysis of 1979–2022 daily mean streamflows at 19 percentiles was computed using a non-parametric Mann-Kendall trend test (Hirsch and others, 2015). Associated basin characteristic raster layers that are currently used in StreamStats for the DRB, including percentage sand in soil, percentage poorly drained soils, percentage urban land use, mean annual precipitation, mean winter precipitation (December–February), and soil hydraulic conductivity, are included in this data release. Citations: Granato, G.E., 2009, Computer programs for obtaining and analyzing daily mean streamflow data from the U.S. Geological Survey National Water Information System Web Site: U.S. Geological Survey Open-File Report 2008–1362, 123 p. on CD-ROM, 5 appendixes, https://pubs.usgs.gov/publication/ofr20081362 Hirsch R.M., DeCicco L.A., 2015, User Guide to Exploration and Graphics for RivEr Trends (EGRET) and dataRetrieval: R Packages for Hydrologic Data: U.S. Geological Survey Techniques and Methods 4-A10, https://pubs.usgs.gov/tm/04/a10/ Stuckey, M.H., 2016, Estimation of daily mean streamflow for ungaged stream locations in the Delaware River Basin, water years 1960–2010: U.S. Geological Survey Scientific Investigations Report 2015–5157, 42 p., http://dx.doi.org/10.3133/sir20155157

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.

Nitrogen, phosphorus, and suspended-sediment loads, and changes in loads, in rivers across the Chesapeake Bay watershed have been calculated using monitoring data from the Chesapeake Bay Nontidal Network (NTN) stations for the period 1985 through 2018 Nutrient and suspended-sediment loads and changes in loads were determined by applying a weighted regression approach called WRTDS (Weighted Regression on Time, Discharge, and Season). A recently published extension of WRTDS allows users to separate these estimates into high- and low-flow conditions. This data release contains (1) a table of daily high- and low-flow concentration and load estimates for NTN stations between 1985 - 2018 and (2) an R file that contains the flow-separation functions. First posted: September 2020 (available from author) Revised: November 2021 (version 1.1)

Estimates of various low-flow statistics were computed at 66 ungaged stream locations throughout New Jersey during the 2021 water year using methods in the published reports, 1) Streamflow characteristics and trends in New Jersey, water years 1897-2003 (Watson and others, 2005) and 2) Implementation of MOVE.1, censored MOVE.1, and piecewise MOVE.1 low-flow regressions with applications at partial-record streamgaging stations in New Jersey (Colarullo and others, 2018). The estimates are computed as needed for use in water resources permitting, assessment, and management by the New Jersey Department of Environmental Protection. The data release includes the stream name, location, drainage area, method of estimation, lowest annual and winter average flows, and the 75 percent flow duration computed during the 2021 water year. The data are provided in plain text file and ArcGIS shapefile formats. References for publications cited: - Colarullo, S.J., Sullivan, S.L., and McHugh, A.R., 2018, Implementation of MOVE.1, censored MOVE.1, and piecewise MOVE.1 low-flow regressions with applications at partial-record streamgaging stations in New Jersey: U.S. Geological Survey Open-File Report 2018-1089, 20 p., accessed March 31, 2022, at https://doi.org/10.3133/ofr20181089. - Watson, K.M., Reiser, R.G., Nieswand, S.P., and Schopp, R.D., 2005, Streamflow characteristics and trends in New Jersey, water years 1897-2003: U.S. Geological Survey Scientific Investigations Report 2005-5105, 131 p., accessed March 31, 2022, at https://doi.org/10.3133/sir20055105.