Treatment of the Chicot and Evangeline aquifers as a single hydrogeologic unit and use of geostatistical interpolation methods to develop gridded surfaces of water-level altitudes and water-level changes in the Chicot and Evangeline aquifers (undifferentiated) and Jasper aquifer, greater Houston area, Texas, 2021

Abstract

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Status of water-level altitudes and long-term water-level changes in the Chicot and Evangeline (undifferentiated) and Jasper aquifers, greater Houston area, Texas, 2021

“…Color-shaded gridded representations (shaded grids) of the 2021 water-level altitudes measured in wells completed in the Chicot and Evangeline (undifferentiated) and Jasper aquifers were prepared; each color shade represents a 50-ft increment in water-level altitudes to match the contour interval commonly used in previous reports in the annual series of reports depicting the status of water-level altitudes in aquifers in the greater Houston area. The shaded grids are published in a companion data release (Ramage and Braun, 2022). The water-level-altitude grids are approximate, regional-scale depictions of the water-level altitudes in wells in the Chicot and Evangeline (undifferentiated) and Jasper aquifers, and the areal extents and locations of the shaded areas represented by these grids represent the combined effects of total groundwater withdrawals from all groundwater wells screened in the Gulf Coast aquifer system within the shaded area.…”

“…If the computed variance at any given grid cell is equal to or smaller than the overall mean variance for each respective gridded surface for the current and historical year, the data are deemed valid for inclusion in the mapped area depicting water-level-altitude change (Ramage and others, 2022). The datasets of waterlevel-change values (difference between 2021 and historical year water-level-altitude values) are available in Ramage (2022); the grids and their associated variance distribution maps that were produced from the water-level data collected from the network of groundwater-monitoring wells (along with a description of the processes by which these datasets were produced) are included in Ramage and Braun (2022).…”

“…Locations of wells used to construct the 2021 waterlevel-altitude maps for the Chicot and Evangeline (undifferentiated) and Jasper aquifers are presented in Ramage (2022) and Ramage and Braun (2022). Certain water-level-altitude measurements collected during November 2020 through March 2021 were not used to construct the water-level maps presented in this report for the Chicot and Evangeline (undifferentiated) and Jasper aquifers.…”

“…A much smaller proportion of the wells were excluded from consideration when constructing the water-level maps because they were not consistent with water-level altitudes obtained from nearby wells screened in the same aquifer for one of the following reasons: (1) the water-level altitude at the well in question differed appreciably from the water levels measured in other wells in the surrounding area and was deemed to be erroneous or (2) water had been withdrawn recently from the well in question and the water-level altitude at this well was still rising. The companion data release by Ramage and Braun (2022) identifies the water-level-altitude measurements that were used to construct maps of water-level altitudes and water-level changes by using kriging methods for each aquifer. Of the 590 observation wells where water-level measurements were made in the study area, measurements from 527 wells were used in the creation of water-level-altitude maps.…”

“…Of the 590 observation wells where water-level measurements were made in the study area, measurements from 527 wells were used in the creation of water-level-altitude maps. Individual water-level altitudes measured at each well for the Chicot and Evangeline (undifferentiated) and Jasper aquifers and associated metadata are provided in companion data releases (Ramage, 2022;Ramage and Braun, 2022).…”