Regional precipitation viability affects irrigation water demand on an aquifer, aquifer recharge, and the density of wells and irrigation systems required for successful agriculture and water supplies. These factors all affect any required water withdrawal allocations from an aquifer. Therefore, knowledge of the precipitation variability over a highly irrigated region, such as the area within the Imperial Valley Water Authority (IVWA), should provide useful information for the management of ground-water resources in that region. The Illinois State Water Survey (ISWS) has a long-term interest in precipitation measurement and related research. For the past 40 years, the ISWS has operated raingage networks over various time periods in both rural and urban areas. An agreement was reached between the IVWA and the ISWS in spring 1992, and a 25-site network was established in late August 1992. This report documents network construction, operation, maintenance, data reduction, and management during the first year of operation (September 1992-August 1993). This report provides data analyses for the year. Several appendices also document actual raingage sites, instructions for raingage technicians, raingage maintenance information, large precipitation amounts recorded during the year, and monthly precipitation variability at each site.
Data collected are providing new information about the variability of precipitation in the region. The exposure and areal coverage of the network appear to adequately capture the precipitation of the region.
Because of the relatively dense raingage spacing, the network also is providing high-quality data for research purposes. After the second and third years of data collection (September 1993-August 1994 and September 1994-August 1995), matrices of correlation coefficients between each raingage site will be computed on a seasonal, yearly, and three-year basis. The correlation analysis will help identify regions of spatial coherency in the precipitation-producing systems traversing the region, allowing further assessment of the spatial variability of the precipitation. Estimates of the probabilities of different storm paths and precipitation patterns in the area also should be possible because these types of statistics become more stable as the sample size of the database increases.
These data and statistics, in combination with ground-water information, should greatly enhance the ability of the IVWA to accurately and efficiently manage pumpage of water from the local aquifer.Imperial Valley Water AuthorityOpe
