National-Scale Grid to Support Regional Groundwater Availability Studies and a National Hydrogeologic Database
Dates
Publication Date
2018-06-06
Time Period
2017-12-13
Citation
Clark, B.R., Barlow, P.M., Peterson, S.M., Hughes, J.D., Reeves, H.W., and Viger, R.J., 2018, National-scale grid to support regional groundwater availability studies and a national hydrogeologic database: U.S. Geological Survey data release, https://doi.org/10.5066/F7P84B24.
Summary
The National Hydrogeologic Grid (NHG) dataset includes a raster and vector representation of 1-km cells defining a uniform grid that encompasses the continental United States. The value of each cell of the raster dataset corresponds to the 1-km cell number defined as 'cellnum' in the attributes of the vector data. The NHG consists of 4,000 rows and 4,980 columns, numbered from the top left corner of the grid, to correspond to the traditional row and column numbering system of the MODFLOW groundwater-flow simulation code (Hughes and others, 2017; Langevin and others, 2017). The Albers projection was chosen for the NHG because of the capability to best preserve area, which is crucial in the computation of volume for water-resource investigations [...]
Summary
The National Hydrogeologic Grid (NHG) dataset includes a raster and vector representation of 1-km cells defining a uniform grid that encompasses the continental United States. The value of each cell of the raster dataset corresponds to the 1-km cell number defined as 'cellnum' in the attributes of the vector data. The NHG consists of 4,000 rows and 4,980 columns, numbered from the top left corner of the grid, to correspond to the traditional row and column numbering system of the MODFLOW groundwater-flow simulation code (Hughes and others, 2017; Langevin and others, 2017). The Albers projection was chosen for the NHG because of the capability to best preserve area, which is crucial in the computation of volume for water-resource investigations (Kuniansky, 2016). The upper left coordinate of the NHG in the Albers projection, in units of meters, is -2553045.0, 3907285.0 with a rotation of zero degrees.
Leaf, A.T., 2023, Automated construction of Streamflow-Routing networks for MODFLOW—Application in the Mississippi Embayment region: U.S. Geological Survey Scientific Investigations Report 2023–5051, 28 p., https://doi.org/10.3133/sir20235051.
The purpose of the NHG is to define a consistent spatial extent and resolution as the foundation for a National Hydrogeologic Database (NHGD). The U.S. Geological Survey (USGS) groundwater community envisions the utility of a NHGD that would serve as an infrastructure for entering, storing, and retrieving hydrogeologic data, including regional datasets developed as part of the USGS Regional Groundwater Availability studies, such as the Coastal Lowlands regional aquifer study. An important building block for such a database is to define the spatial extent and ‘geospatial fabric’ of the framework. The NHG extent was designed to include the area simulated by the National Water Model (NWM) to foster collaboration between the National Weather Service and the USGS on national-scale modeling, though the individual grid cells do not align with the NWM grid because of differing spatial projections. Additionally, the NHG position was created to align with the USGS National Land Cover Database (NLCD) (Homer and Megown, 2015). The NLCD grid contains cells at a spatial resolution of 30 meters. Therefore, the NHG cells (1-km spatial resolution) aligns with the NLCD at intervals of 3 km in the north-south and east-west directions. It is envisioned that applications requiring finer resolution than 1-km would be based on multiples of the NHG cell sizes (such as 250-m or 500-m cells), and would be developed to align with the NHG cells.
