This Geographic Information System dataset contains a shapefile of the watershed drainage area boundaries for the 15 watersheds which were used in the study in Gwinnett County, Georgia. The watersheds were delineated with StreamStats.

This Geographic Information System dataset contains shapefiles of 200-foot stream buffers for the 15 study watersheds in Gwinnett County, Georgia. The stream buffers are based on flowlines from the high resolution, 1:24,000-scale National Hydrography Dataset.

This Geographic Information System dataset contains shapefiles of 200-foot stream buffers for the 15 study watersheds in Gwinnett County, Georgia. The stream buffers are based on flowlines from the high resolution, 1:24,000-scale National Hydrography Dataset.

The dataset contains annual and model calibration period streamwater constituent load and yield estimates for 13 watersheds in Gwinnett County, Georgia for the water years 2003 to 2020. Loads and yields were estimated for 12 water-quality constituents: total suspended solids, suspended sediment concentration, total nitrogen, total nitrate plus nitrite, total phosphorus, dissolved phosphorus, total organic carbon, total calcium, total magnesium, total lead, total zinc, and total dissolved solids. The USGS LOADEST load estimation software, which employs a regression-model estimation approach, was used for constituents that had at least a minimal relation with the model explanatory variables, as indicated by concentration model R-square >0.20. The Beale ratio estimator was used to estimate loads for constituents that had weak concentration-model relations, concentration model R-squares <0.20. Loads and yields are provided for the 13 individual study watersheds and for the study watersheds area. The period of loads available varies by watershed depending upon when monitoring and constituent analysis started. Uncertainties in load and yield estimates that were calculated using LOADEST are provided as 95-percent confidence intervals of the estimates.

This data release contains 15 datasets and associated metadata of watershed characteristics and data related to stream water quality and constituent load estimation for 15 study watersheds in Gwinnett County, Georgia. Dataset periods vary but range within 2000 to 2021. The 15 datasets are organized as individual child items. The data release includes three Geographic Information System shapefiles: (1) 01: Watersheds shapefile for the 15 study watersheds in Gwinnett County, Georgia; (2) 02: Stormwater drainage areas shapefile for the 15 study watersheds in Gwinnett County, Georgia, August 2021; and (3) 03: 200-foot stream buffer shapefiles for 15 watersheds in Gwinnett County, Georgia. The data release includes four comma separated value (csv) format datasets related to watershed characteristics: (1) 04: National Land Cover Database land cover at 15 watersheds in Gwinnett County, Georgia from 2001 to 2019; (2) 05: Impervious areas within 15 watersheds in Gwinnett County, Georgia from 2000 to 2020; (3) 06: Property parcel building construction dates and densities in 15 watersheds in Gwinnett County, Georgia in 2021; and (4) 07: Population density in 15 watersheds in Gwinnett County, Georgia from 2000 to 2020. The data release also includes the following eight csv format datasets related to stream water quality and constituent load estimation: (1) 08: Daily average stream base flow at 14 watersheds in Gwinnett County, Georgia for water years 2002-2020; (2) 09: Streamwater quality assurance sample results for 19 water-quality constituents in 15 watersheds in Gwinnett County, Georgia for years 2000-2020; (3) 10: Laboratory standard reference samples for the Gwinnett County, Georgia study for years 2014-2020; (4) 11: Streamwater sample constituent concentration outliers from 15 watersheds in Gwinnett County, Georgia for water years 2003-2020; (5) 12: Model calibration data for fitting regression models used to estimate streamwater loads for 12 constituents in 13 watersheds in Gwinnett County, Georgia for water years 2003-2020; (6) 13: Models coefficients and statistics for regression models used to estimate streamwater loads for 12 water-quality constituents in 13 watersheds in Gwinnett County, Georgia for water years 2003-2020 (includes 488 portable document format files (pdf) with reports and plots for evaluating model fits); (7) 14: LOADEST estimation dataset used to estimate streamwater loads for 12 constituents in 13 watersheds in Gwinnett County, Georgia for water years 2003-2020; and (8) 15: Streamwater load and yield estimates for 12 constituents in 13 watersheds in Gwinnett County, Georgia for water years 2003-2020.

This dataset contains the percentage of 14 National Land Cover Database (NLCD) land cover classes within the drainage areas of 15 watersheds in Gwinnett County, Georgia from 2001 to 2019. The dataset includes scenes from eight years, 2001, 2004, 2006, 2008, 2011, 2013, 2016, and 2019, which were analyzed using a consistent approach so that they could be used to assess land cover changes. The NLCD dataset is derived from Landsat imagery and has a grid size of 30 meters. The fourteen land cover classes were categorized into eight land cover groups to simplify the presentation of watershed land cover characteristics (1. developed, low intensity; 2. developed, medium intensity; 3. developed, high intensity; 4. developed, open space; 5. agriculture; 6. forest; 7. fields/open; and 8. water/wetlands).

This dataset contains the daily average base flow, as determined by hydrograph separation, for 14 watersheds in Gwinnett County, Georgia for October 2001 through September 2020. Hydrograph separations were done using the Web-based Hydrograph Analysis Tool (WHAT) using the simple local minimum method on the daily average streamflows, which are also provided in this dataset. Base flow along with the calculated base-flow index (the proportion of base flow to total flow) were used to characterize groundwater recharge and the relative degree of storm runoff in the watersheds. Base flow was also used as predictor variable in models for estimating streamwater constituent loads for 12 water-quality constituents at 13 of the study watersheds.

This dataset contains the percentages of impervious areas within the drainage areas of 15 watersheds in Gwinnett County, Georgia from 2000 to 2020. The dataset includes data from 16 years, 2000, 2005, 2006, and annually from 2008 to 2020. The dataset was derived from impervious area coverages provided from the Gwinnett County Department of Public Utilities. These coverages were determined from 1:1,200-scale aerial photography with a 1-meter square grid size created by digitizing polygons of impervious surfaces. Watershed imperviousness was determined for various land cover types that were provided with the impervious area coverages. These included transportation and buildings land cover types for all impervious area scenes and additionally for recreation, structures, and utilities land cover types for scenes from 2008 through 2020. Impervious areas within a 200-ft stream buffer from National Hydrography Dataset flowlines were also determined for 2019.

The dataset contains model coefficients and statistics for the 488 regression models used to estimate streamwater constituent loads for 13 watersheds in Gwinnett County, Georgia for two calibration periods, water years 2003-2010 and 2010-2020. Model terms were selected from an 11-parameter equation, which was a function of discharge, base flow, season, turbidity, and time (trend), using a forward stepwise ordinary least squares regression approach. Model coefficients were fit using U.S. Geological Survey (USGS) LOADEST load estimation software. Models were fit both with and without turbidity explanatory variables for 12 water-quality constituents: total suspended solids, suspended sediment concentration, total nitrogen, total nitrate plus nitrite, total phosphorus, dissolved phosphorus, total organic carbon, total calcium, total magnesium, total lead, total zinc, and total dissolved solids. The dataset includes a summary of sample concentrations used to calibration the models (period of samples collected, number of concentrations, number of censored concentrations, and number of outliers removed), model coefficients, and selected model statistics (concentration and load model R-squares, estimated residual variance, serial correlation in the model residuals, and Turnbull-Weiss normality test statistic of residuals). Portable document format files of LOADEST output are provided for each model in a “zip” file that contain model diagnostic statistics and plots for evaluating model fits.

The dataset contains model coefficients and statistics for the 488 regression models used to estimate streamwater constituent loads for 13 watersheds in Gwinnett County, Georgia for two calibration periods, water years 2003-2010 and 2010-2020. Model terms were selected from an 11-parameter equation, which was a function of discharge, base flow, season, turbidity, and time (trend), using a forward stepwise ordinary least squares regression approach. Model coefficients were fit using U.S. Geological Survey (USGS) LOADEST load estimation software. Models were fit both with and without turbidity explanatory variables for 12 water-quality constituents: total suspended solids, suspended sediment concentration, total nitrogen, total nitrate plus nitrite, total phosphorus, dissolved phosphorus, total organic carbon, total calcium, total magnesium, total lead, total zinc, and total dissolved solids. The dataset includes a summary of sample concentrations used to calibration the models (period of samples collected, number of concentrations, number of censored concentrations, and number of outliers removed), model coefficients, and selected model statistics (concentration and load model R-squares, estimated residual variance, serial correlation in the model residuals, and Turnbull-Weiss normality test statistic of residuals). Portable document format files of LOADEST output are provided for each model in a “zip” file that contain model diagnostic statistics and plots for evaluating model fits.