This dataset represents one of three derived outlets or "pour points" for each 12-digit hydrologic unit (HU12) in the Watershed Boundary Dataset (WBD) snapshot delivered with NHDPlus V2.1. The three related pour point locations, each delivered in a stand-alone dataset, are: "from" (fpp) and "to" (tpp) points that identify the location where flow leaves the HU12 polygon based on a flow direction raster, and a third "vector pour point" (vpp) selected "upstream" used to identify flow confluences near the "from" and "to" pour point locations. The points are derived from the NHDPlus V2.1 flow direction rasters and the WBD snapshot delivered with NHDPlus V2.1. This metadata document describes the "vector" pourpoints (vpp).

This dataset represents one of three derived outlets or "pour points" for each 12-digit hydrologic unit (HU12) in the Watershed Boundary Dataset (WBD) snapshot delivered with NHDPlus V2.1. The three related pour point locations, each delivered in a stand-alone dataset, are: "from" (fpp) and "to" (tpp) points that identify the location where flow leaves the HU12 polygon based on a flow direction raster, and a third "vector pour point" (vpp) selected "upstream" used to identify flow confluences near the "from" and "to" pour point locations. The points are derived from the NHDPlus V2.1 flow direction rasters and the WBD snapshot delivered with NHDPlus V2.1. This metadata document describes the "from" pourpoints (fpp).

This dataset represents one of three derived outlets or "pour points" for each 12-digit hydrologic unit (HU12) in the Watershed Boundary Dataset (WBD) snapshot delivered with NHDPlus V2.1. The three related pour point locations, each delivered in a stand-alone dataset, are: "from" (fpp) and "to" (tpp) points that identify the location where flow leaves the HU12 polygon based on a flow direction raster, and a third "vector pour point" (vpp) selected "upstream" used to identify flow confluences near the "from" and "to" pour point locations. The points are derived from the NHDPlus V2.1 flow direction rasters and the WBD snapshot delivered with NHDPlus V2.1. This metadata document describes the "to" pourpoints (tpp).

This dataset represents one of three derived outlets or "pour points" for each 12-digit hydrologic unit (HU12) in the Watershed Boundary Dataset (WBD) snapshot delivered with NHDPlus V2.1. The three related pour point locations, each delivered in a stand-alone dataset, are: "from" (fpp) and "to" (tpp) points that identify the location where flow leaves the HU12 polygon based on a flow direction raster, and a third "vector pour point" (vpp) selected "upstream" used to identify flow confluences near the "from" and "to" pour point locations. The points are derived from the NHDPlus V2.1 flow direction rasters and the WBD snapshot delivered with NHDPlus V2.1. This metadata document describes the "to" pourpoints (tpp).

This USGS data release consists of three datasets representing three derived outlets or "pour points" for each 12-digit hydrologic unit (HU12) in the Watershed Boundary Dataset (WBD) snapshot delivered with NHDPlus V2.1. The three related pour point locations, each delivered in a stand-alone dataset, are: "from" (fpp) and "to" (tpp) points that identify the location where flow leaves the HU12 polygon based on a flow direction raster, and a third "vector pour point" (vpp) selected "upstream" used to identify flow confluences near the "from" and "to" pour point locations. The points are derived from the NHDPlus V2.1 flow direction rasters and the WBD snapshot delivered with NHDPlus V2.1.

A crosswalk table between NHDPlus version 2.1 flowlines (using the unique field COMID) and the Watershed Boundary Dataset (WBD) 12-digit-hydrologic units (HU-12) is provided for the 48 contiguous United States. The crosswalk table provides a WBD HU-12 assignment for every networked flowline in the NHDPlus. In this way, the network developed for navigation and modeling, NHDPlus, is aligned with accounting units of the WBD HU-12s to the extent possible given the assumptions that were made in creating each. A crosswalk table for NHDPlus isolated sinks was produced by a simple overlay process where the sinks were assigned HU-12 values based on their position relative to the WBD snapshot HU-12s. This table was integrated with the flowline associations into one crosswalk table for both feature types. There is good alignment between aggregated NHDPlus catchments and WBD HU-12 units in many locations. These are areas where the flows and chemical or nutrient loads that are accumulated leave the HU-12 at a single outlet and are passed down to the next HU-12 downstream (or to the coast) as is assumed in the WBD model. A second pass through the data was made to account for any secondary outlet from each HU-12. The location of a secondary outlet with a significant drainage from that HU was identified in the alignment with NHDPlus. This resulted in a reduction in areas of mismatch as well as an improved crosswalk table. The crosswalk table should be used with caution in areas where efforts could be made to improve the data. For example, with medium-resolution NHD, a better definition of flow direction of the flowlines in Southern Florida would result in more flowlines being included in the “networked” flowlines with catchments, and that, in turn, would result in better alignment between NHDPlus catchments and HU-12s. Correcting errors in either the medium-resolution NHD or WBD would improve the alignment between the two datasets.

A crosswalk table between NHDPlus version 2.1 flowlines (using the unique field COMID) and the Watershed Boundary Dataset (WBD) 12-digit-hydrologic units (HU-12) is provided for the 48 contiguous United States. The crosswalk table provides a WBD HU-12 assignment for every networked flowline in the NHDPlus. In this way, the network developed for navigation and modeling, NHDPlus, is aligned with accounting units of the WBD HU-12s to the extent possible given the assumptions that were made in creating each. A crosswalk table for NHDPlus isolated sinks was produced by a simple overlay process where the sinks were assigned HU-12 values based on their position relative to the WBD snapshot HU-12s. This table was integrated with the flowline associations into one crosswalk table for both feature types. There is good alignment between aggregated NHDPlus catchments and WBD HU-12 units in many locations. These are areas where the flows and chemical or nutrient loads that are accumulated leave the HU-12 at a single outlet and are passed down to the next HU-12 downstream (or to the coast) as is assumed in the WBD model. A second pass through the data was made to account for any secondary outlet from each HU-12. The location of a secondary outlet with a significant drainage from that HU was identified in the alignment with NHDPlus. This resulted in a reduction in areas of mismatch as well as an improved crosswalk table. The crosswalk table should be used with caution in areas where efforts could be made to improve the data. For example, with medium-resolution NHD, a better definition of flow direction of the flowlines in Southern Florida would result in more flowlines being included in the “networked” flowlines with catchments, and that, in turn, would result in better alignment between NHDPlus catchments and HU-12s. Correcting errors in either the medium-resolution NHD or WBD would improve the alignment between the two datasets.

This tabular data set represents average topgraphic wetness index 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 Topgraphic Wetness Index is a steady state index that’s used to predict areas susceptible to saturated land surfaces and areas that carry the potential to produce overland flow. The index is represented by ln (a/tan(beta)), where ln is the Napierian logarithm, a is the upslope area per unit contour length, and tan/(beta) is the slope gradient (Wolock and McCabe, 1995). The source data for average topgraphic wetness index used here was produced by David Wolock (United States Geological Survey, written communic., 2012). Units are ln(m); where ln(m) = the Naperian logarithm of length, where length is measured in meters. 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 average topgraphic wetness index 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 Topgraphic Wetness Index is a steady state index that’s used to predict areas susceptible to saturated land surfaces and areas that carry the potential to produce overland flow. The index is represented by ln (a/tan(beta)), where ln is the Napierian logarithm, a is the upslope area per unit contour length, and tan/(beta) is the slope gradient (Wolock and McCabe, 1995). The source data for average topgraphic wetness index used here was produced by David Wolock (United States Geological Survey, written communic., 2012). Units are ln(m); where ln(m) = the Naperian logarithm of length, where length is measured in meters. 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 average topgraphic wetness index 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 Topgraphic Wetness Index is a steady state index that’s used to predict areas susceptible to saturated land surfaces and areas that carry the potential to produce overland flow. The index is represented by ln (a/tan(beta)), where ln is the Napierian logarithm, a is the upslope area per unit contour length, and tan/(beta) is the slope gradient (Wolock and McCabe, 1995). The source data for average topgraphic wetness index used here was produced by David Wolock (United States Geological Survey, written communic., 2012). Units are ln(m); where ln(m) = the Naperian logarithm of length, where length is measured in meters. 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).