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Title:Operation of Rain Gauge and Groundwater Monitoring Networks for the Imperial Valley Water Authority - Year Ten : September 2001 - August 2002
Author(s):Wehrmann, H. Allen; Westcott, Nancy E.; Scott, Robert W.
Subject(s):groundwater monitoring
precipitation monitoring
Geographic Coverage:Mason County, Illinois; Tazewell County, Illinois
Abstract:The Illinois State Water Survey (ISWS), under contract to the Imperial Valley Water Authority (IVWA), has operated a network of rain gauges in Mason and Tazewell Counties since August 1992. The ISWS also established a network of groundwater observation wells in the Mason-Tazewell area in 1994 that is monitored by the IVWA. The purpose of the rain gauge network and the groundwater observation well network is to collect long-term data to determine the impact of groundwater withdrawals in dry periods and during the growing season, and the rate at which the aquifer recharges. This report presents data accumulated from both networks since their inception through August 2002. Precipitation is recorded continuously at 20 rain gauges. Groundwater levels are measured the first of each month at 13 observation wells. The database from these networks consists of ten years of precipitation data and eight years of groundwater observations. During the preparation of the data for this report, it was found that the annual precipitation total at site 16 has been somewhat higher than at the surrounding gauges for the past six years, with the annual difference between site 16 and its neighbors increasing during the last three years (annual difference of 11.6 inches in 2001-2002). The gauge at this site was replaced on May 23, 2002, and the monthly totals were comparable with those at surrounding gauges. Accordingly, the annual spatial patterns for the past six years were redrawn omitting the precipitation from site 16 and replace maps from previous reports. Site 16 data also were omitted from the annual average network precipitation tabulations and from the average number of precipitation-days and events for the past six years (1996-1997 through 2001-2002). For the current year, the network received an average of 39.91 inches of precipitation, 4.02 inches greater than the network 10-year average precipitation. In 2002, groundwater levels in wells close to the Illinois River peaked above levels observed at any time since the 1995 record highs, closely following Illinois River peak stages. Groundwater levels in the rest of the observation wells, more distant from the Illinois River, also showed their highest levels since 1995. Groundwater levels in many wells rose throughout the winter, starting from seasonal lows in October 2001. January 2002 water levels in most wells were above those observed in December 2001. Pronounced water level rises were seen in the river wells (Mason-Tazewell Observation Well or MTOW-5 and MTOW-9) in February-March, followed by wells MTOW-2 and MTOW-10 in April-May, then by the rest of the wells (except MTOW-11) between May and June. Total irrigation for the June-September period was estimated to be 47 billion gallons, the second highest total since 1995 and tied with the 2001 irrigation season estimate. This can be attributed, in part, to the growth of irrigation systems in the Imperial Valley, which now has 1,839 systems. The timing of the rainfall during the irrigation season probably was more crucial, however. For June-August, 12.23 inches of the total network average of 13.59 inches (90 percent of the rain) fell in 15 days of the 92-day period (16 percent of the days).
Issue Date:2004
Publisher:Illinois State Water Survey
Genre:Technical Report
Sponsor:Imperial Valley Water Authority
Rights Information:This document is a product of the Illinois State Water Survey, produced for the Imperial Valley Water Authority. It has been selected and made available by the Illinois State Water Survey and the University Library, University of Illinois at Urbana-Champaign. It is intended for research and educational use, and proper attribution is requested.
Date Available in IDEALS:2014-09-24

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