During April 2020, staff of the Upper Big Blue Natural Resources District measured roughly 500 observation wells throughout the nine-county district. The goal of these well measurements is to determine an average water level change for the district, based on a weighted change from each well. For spring 2020 water level measurements, the NRD staff has determined that the average groundwater level change shows an increase of 3.67 feet from last spring. The findings show that the spring 2020 average groundwater level is 8.78 feet above the allocation trigger. Thus, there will be no allocation restrictions for the 2021 irrigation season.
Observation wells are measured in the spring of each year, allowing the water table to rebound from the previous irrigation season. The wells that are measured are uniformly distributed throughout the district to provide an accurate profile of the average groundwater level change. Each well measured is assigned an area of the district based on distances from other wells. This method of averaging is known as the Thiessen polygon method and gives the average groundwater level change a weighted average.
Last year’s spring 2019 level showed an increase of 1.22 feet and spring 2018 showed an increase of .87 feet. Fluctuations from year to year are common throughout the district. The Upper Big Blue NRD sits above the High Plains Aquifer, which stretches from South Dakota to Texas. This portion of the aquifer is dynamic and different factors like rainfall and pumping affect how the aquifer reacts. In recent years, producers have done an exceptional job of managing use of this water resource.
Along with NRD staff measuring observation wells, all groundwater users are required to annually report their water use. This is how the NRD maintains records on historic groundwater usage. Groundwater user records are very important to the district for making informed management decisions. The 2019 district average groundwater usage was 2.2 inches, which is well below average pumping for the district. The district average groundwater usage is 5.9 inches/year since 2007. Presently, there are 1,241,505 irrigated acres and 12,208 active irrigation wells in the Upper Big Blue NRD.
The NRD’s goal is to hold the average groundwater level at or above the 1978 level. In 2005, the district average groundwater level reached the reporting trigger level, initiating groundwater users to report annual groundwater use to the district and to certify their irrigated acres. If the district average water level falls below the 1978 level (allocation trigger), groundwater allocation will take effect. These measures ensure equitable water usage for all district residents.
For full details, including maps and graphs that show more information about the current and historic groundwater levels, visit www.upperbigblue.org.