DOI: 10.5066/p1k3zpas
title: Soil texture and hydraulic conductivity at a 1-kilometer resolution for the Contiguous United States based on 30-meter resolution data from the Polaris database.

description: The U.S. Geological Survey (USGS) Integrated Water Availability Assessments (IWAAs) Program is designed to deliver nationally consistent assessments of water supplies for human and ecological needs, and to identify factors that influence water availability. In support of these studies, a National-Extent Hydrogeologic Framework (NEHF) is under development. The NEHF is a three-dimensional digital representation of the subsurface of the United States. Three depth zones are of particular interest: a shallow zone within which groundwater interacts with streams (meters to tens of meters); an intermediate zone comprised of potable water (tens to hundreds of meters); and deep, saline groundwater (hundreds of meters to kilometers). Laterally, the NEHF will be developed at a 1-kilometer (km) resolution across the continental United States (CONUS). Vertically, the NEHF will extend from the land surface to a depth of several kilometers. The vertical resolution of the NEHF will vary, with relatively fine resolution at shallow depth and relatively coarse resolution at depth. Soils are a part of the shallow groundwater system, and soil properties can be used to develop predictive models for characteristics of the deeper subsurface. The NEHF is utilizing the Polaris soil properties data set (Chaney et al, 2019) because it harmonizes the previously published Soil Survey Geographic Database (SSURGO, USDA NRCS, 2023) and the National Cooperative Soil Survey Soil Characterization (USDA, 2023) databases. The Polaris database includes soil properties such as soil texture, which is the percentage of sand, silt, or clay present in a soil as well as saturated hydraulic conductivity (Ksat), which indicates the ease with which water can move through the soil. Soil hydraulic conductivity can vary spatially, and representative values of a heterogeneous distribution can be obtained in one of several ways, including the geometric mean. The geometric mean provides an estimate of the mean value of a log-normal distribution; soil hydraulic conductivity is often log-normally distributed. Raster data are provided at a 30-meter (m) resolution across the contiguous United States for six depth zones: 0-5 centimeters (cm), 5-15 cm, 15-30 cm, 30-60 cm, 60-100 cm, and 100-200 cm. The rasters in this Data Release provide a weighted average value over the six depth intervals rescaled to a resolution of 1-km and 100-m. These rasters can be used in the development of the NEHF and for other purposes. A total of 11 rasters are included in the data release. They include the following: Soil Texture (SoilTextureRasters_100m.7z; SoilTextureRasters_1km.7z): Values range from 1 - 99% (values may not add up to 100% as they represent a weighted mean, as well as a change in resolution from the source files). The specific ranges for each property can be found in the metadata.xml files for each raster. Mean Percent Sand at 1-km and 100-m resolution (2 rasters: sand_1km.tif and sand_100m.tif). Mean Percent Clay at 1-km and 100-m resolution (2 rasters: clay_1km.tif and clay_100m.tif) Mean Percent Silt at 1-km and 100-m resolution (2 rasters: silt_1km.tif and silt_100m.tif) Classified Soil Texture at 1km (1 raster: texture_3class.tif): The above three soil texture rasters were classified into three categories based on the percentages of each soil property within a 1-km cell. Saturated Hydraulic Conductivity (SaturatedHydraulicConductivity_100m.7z; SaturatedHydraulicConductivity_1km.7z): Values range from -2.4 to 2.1 in the logarithmic scale, and 0-126.3 for the arithmetic mean. The specific ranges for each property can be found in the metadata.xml files for each raster. Logarithmic Saturated Hydraulic Soil Conductivity (KSat) at 1-km and 100-m resolution (2 rasters: KSat_Log_100m.tif; KSat_Log_100m.tif): KSat rasters in the Polaris Soils database were provided as logarithmic values. Arithmetic Saturated Hydraulic Soil Conductivity (KSat) at 1-km and 100-m resolution (2 rasters: KSat_Arithmetic_100m.tif; KSat_Arithmetic_100m.tif): The logarithmic values were transformed into the arithmetic values to determine a geometric mean value.