Title: Hydrogeologic characteristics and geospatial analysis of water-table changes in the alluvium of the lower Arkansas River Valley, southeastern Colorado, 2002, 2008, and 2015 Prepared in cooperation with the Lower Arkansas Valley Water Conservancy District By Michael J. Holmberg 2017 U.S. Geological Survey Scientific Investigations Map 3378 U.S. Geological Survey data release https://doi.org/10.5066/F71G0JF6 ABSTRACT: The U.S. Geological Survey in cooperation with the Lower Arkansas Valley Water Conservancy District measures groundwater levels periodically in about 100 wells completed in the alluvial material of the Arkansas River Valley in Pueblo, Crowley, Otero, Bent, and Prowers Counties in southeastern Colorado, of which 95 are used for the analysis in this report. The purpose of this report is to provide information to water-resource administrators, managers, planners, and users about groundwater characteristics in the alluvium of the lower Arkansas Valley extending roughly 150 miles between Pueblo Reservoir and the Colorado-Kansas State line. This report includes three map sheets showing (1) bedrock altitude at the base of the alluvium of the lower Arkansas Valley; (2) estimated spring-to-spring and fall-to-fall changes in water-table altitude between 2002, 2008, and 2015; and (3) estimated saturated thickness in the alluvium during spring and fall of 2002, 2008, and 2015, and thickness of the alluvium in the lower Arkansas Valley. Water-level changes were analyzed by geospatial interpolation methods. Available data included all water-level measurements made between January 1, 2001, and December 31, 2015; however, only data from fall and spring of 2002, 2008, and 2015 are mapped in this report. To account for the effect of John Martin Reservoir in Bent County, Colorado, lake levels at the reservoir were assigned to points along the approximate shoreline and were included in the water-level dataset. After combining the water-level measurements and lake levels, inverse distance weighting was used to interpolate between points and calculate the altitude of the water table for fall and spring of each year for comparisons. Saturated thickness was calculated by subtracting the bedrock surface from the water-table surface. Thickness of the alluvium was calculated by subtracting the bedrock surface from land surface using a digital elevation model. In order to analyze the response of the alluvium to varying environmental and anthropogenic conditions, the percentage of area of the lower Arkansas Valley showing an absolute change of 3 feet or less was calculated for each of the six water-table altitude change maps. For fall water-table altitude change maps, the periods between 2002 and 2008, 2008 and 2015, and 2002 and 2015 showed that 86.5 percent, 85.2 percent, and 66.3 percent of the study area, respectively, showed a net change of 3 feet or less. In the spring water-table altitude change maps these periods showed a net change of 3 feet or less in 94.4 percent, 96.1 percent, and 90.2 percent of the study area, respectively. While the estimated change in water-table altitude was slightly greater and more variable in fall-to-fall comparisons, these high percentages of area with relatively small net changes indicated that, at least in comparisons of the years presented, there was not a large amount of fluctuation in the altitude of the water table. The saturated thickness in the lower Arkansas Valley was between 25 and 50 feet in 34.4 to 35.9 percent of the study area, depending on the season and year. Between 30.2 and 35.6 percent of the area showed saturated thicknesses between 0 and 25 feet. Less than 1 percent of the area showed a saturated thickness greater than 200 feet in all mapped seasons and years. DISCLAIMERS: Any use of trade, product or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Geological Survey. Although this information product, for the most part, is in the public domain, it also may contain copyrighted material as noted in the text. Permission to reproduce copyrighted items for other than personal use must be secured from the copyright owner. This database, identified as SIM 3378, has been approved for release by the U.S. Geological Survey (USGS). Although this database has been subjected to rigorous review and is substantially complete, the USGS reserves the right to revise the data pursuant to further analysis and review. Furthermore, it is released on condition that neither the USGS nor the United States Government may be held liable for any damages resulting from its authorized or unauthorized use. Although these data have been processed successfully on a computer system at the U.S. Geological Survey, no warranty, expressed or implied is made regarding the display or utility of the data on any other system, or for general or scientific purposes, nor shall the act of distribution constitute such warranty. The USGS or the U.S. Government shall not be held liable for improper or incorrect use of the data described and/or contained herein. REPORT FILES: The pamphlet and maps for this report are located at and can be downloaded via the Web from at the U.S. Geological Survey publications website at https://doi.org/10.3133/sim3378 List of files: 00ReadMe.txt sim3378_pamphlet.pdf sim3378_sheet1.pdf sim3378_sheet2.pdf sim3378_sheet3.pdf sim3387_appendix1.xlsx sim3387_appendix2.pdf DATA RELEASE FILES The GIS database for this report is located at and can be downloaded via the Web from ScienceBase at https://doi.org/10.5066/F71G0JF6 Alluvium_Thickness_metadata.xml Bedrock_Contours_metadata.xml LAV_StudyArea_Boundary_metadata.xml SaturatedThickness_Fall2002_metadata.xml SaturatedThickness_Fall2008_metadata.xml SaturatedThickness_Fall2015_metadata.xml SaturatedThickness_Spring2002_metadata.xml SaturatedThickness_Spring2008_metadata.xml SaturatedThickness_Spring2015_metadata.xml WaterLevelChange_Fall2002_to_Fall2008_metadata.xml WaterLevelChange_Fall2002_to_Fall2015_metadata.xml WaterLevelChange_Fall2008_to_Fall2015_metadata.xml WaterLevelChange_Spring2002_to_Spring2008_metadata.xml WaterLevelChange_Spring2002_to_Spring2015_metadata.xml WaterLevelChange_Spring2008_to_Spring2015_metadata.xml Well_Inventory_metadata.xml Bedrock_Contours.shp LAV_StudyArea_Boundary.shp Well_Inventory.shp. Alluvium_Thickness.tfw (.tif/.tif.aux.xml/tif.ovr/.tif.xml) SaturatedThickness_Fall2002.tfw SaturatedThickness_Fall2008.tfw SaturatedThickness_Fall2015.tfw SaturatedThickness_Spring2002.tfw SaturatedThickness_Spring2008.tfw SaturatedThickness_Spring2015.tfw WaterLevelChange_Fall2002_to_Fall2008.tfw WaterLevelChange_Fall2002_to_Fall2015.tfw WaterLevelChange_Fall2008_to_Fall2015.tfw WaterLevelChange_Spring2002_to_Spring2008.tfw WaterLevelChange_Spring2002_to_Spring2015.tfw WaterLevelChange_Spring2008_to_Spring2015.tfw HOW TO OBTAIN THE DIGITAL MAP AND PAMPHLET FILES: The map sheets and accompanying pamphlet can be obtained via the Internet from the U.S. Geological Survey publications website. Go to the web page at https://doi.org/10.3133/sim3378/ and follow the directions to download the files. The main product is a Portable Document Format (.pdf) map, which requires Adobe Acrobat for viewing. These Portable Document Format (PDF) files can be downloaded, from which paper copies may be printed. Acrobat software runs on a variety of systems, and is available for download free of charge from Adobe at http://www.adobe.com. Suggested citation: Holmberg, M.J., 2017, Hydrogeologic characteristics and geospatial analysis of water-table changes in the alluvium of the lower Arkansas River Valley, southeastern Colorado, 2002, 2008, and 2015: U.S. Geological Survey Scientific Investigations Map 3378, pamphlet XX p., 3 sheets, scale 1:130,000 and 1:575,000, https://doi.org/10.3133/sim3378. HOW TO OBTAIN THE DIGITAL GIS FILES: The digital GIS files constituting the geologic map database of this report can be obtained from the U.S. Geological Survey via the Internet from ScienceBase: ScienceBase link: https://doi.org/10.5066/F71G0JF6. Suggested citation: Holmberg, M.J., 2017, Data release--Hydrogeologic characteristics and geospatial analysis of water-table changes in the alluvium of the lower Arkansas River Valley, southeastern Colorado, 2002, 2008, and 2015: U.S. Geological data release, https://doi.org/10.5066/F71G0JF6. ArcReader may be downloaded free of charge from http://www.esri.com/software/arcgis/arcreader/download for viewing data files included in this report. These maps are offered as an online-only, digital publication. Users should be aware that, because of differences in rendering processes and pixel resolution, some slight distortion of scale may occur when viewing it on a computer screen or when printing it on an electronic plotter, even when it is viewed or printed at its intended publication scale.