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<br />~~~A~O <br />U~~J,)0 <br /> <br />GROUND-WATER HYDROGRAPHS, 1970-87, AND WATER-LEVEL DATA, 1986-87, <br />FOR THE NORTHERN HIGH PLAINS OF COLORADO <br /> <br />Bg Raymond L. Reed <br /> <br />ABSTRACT <br /> <br />During the winter of 1986-87, water-level measurements were made in 637 of <br />the 641 wells that currently (1987) are monitored by the U.S. Geological <br />Survey on the northern High Plains of Colorado. Hydrographs of water-level <br />measurements for 1970-87 are included for each of these wells. Water-level <br />measurements for the winter of 1986-87 are listed in a table; this table also <br />lists the local number, geohydrologic unites), depth, and altitude of land <br />surface of each of the 641 wells. <br /> <br />INTRODUCTION <br /> <br />The northern High Plains of Colorado is an area of about 9,500 mi2 in the <br />eastern part of the State (fig. 1). The boundaries of the High Plains of <br />Colorado are the State line on the east and the limit of the Ogallala Forma- <br />tion of late Tertiary age on the north, west, and south. The Ogallala Forma- <br />tion is an unconsolidated or partly consolidated deposit of gravel, sand, <br />silt, and clay and is the major aquifer in the northern High Plains (Borman <br />and Meredith, 1983). <br /> <br />The ground-water level in much of the High Plains has been declining <br />because pumping for irrigation is removing water from storage (Borman, 1983). <br />Knowledge of the magnitude and extent of water-level change is necessary for <br />management of the ground-water resource. <br /> <br />Reports about water levels in the northern High Plains of Colorado have <br />been published periodically since the late 1950's. During the late 1950's and <br />the early 1960's, the U.S. Geological Survey investigated ground-water re- <br />sources in the northern High Plains. Data from these investigations were <br />published initially as data releases accompanying U.S. Geological Survey <br />water-supply papers. During the late 1960's and the early 1970's, water-level <br />data for 5-year periods were published in basic-data releases by the Colorado <br />Water Conservation Board. From the late 1970's until 1983, water-level <br />information for the preceding 5 years was published annually as U.S. Geologi- <br />cal Survey open-file reports. Seventeen years of water-level data were <br />published by Reed (1987). This report contains water-level information for an <br />18-year period and includes much of the data from these previous reports. <br /> <br />Water-level data were obtained during water year 1987 (October 1, 1986, <br />through September 30, 1987) in the northern High Plains of Colorado as part of <br /> <br />1 <br />