DWR_2878158 - Laserfiche WebLink

DISCUSSION During the winter of 2002-2003, water levels were obtained for approximately 650 wells in the Northern High Plains Designated Ground Water Basin. An attempt was made to measure all the wells within a six-week period beginning approximately in late -December 2002. For most of the basin, all wells were measured by the first of February 2003. By measuring the wells in a short time period, it is hoped that seasonal fluctuations will be dampened and that the hydrographs and comparison of water level change will more accurately reflect the true ground water conditions. Unfortunately, it was not possible to obtain measurements in the northern portion of the basin within this time period. For this reason, some of the northern districts averages may not be as representative as in the past. Throughout the Northem High Plains, the water levels continue to show the regional decline that is to be expected when water is being "mined." The past year, along with the last several years, was a very dry in the High Plains and declines accelerated rapidly. The map contained in the back of the report shows the decline in water level over the 10 -year period of 1993 to 2003. The average rate of decline for the past year was almost two and a half times the ten- year average and was double that of last year. The 2001-2002 decline was 1.12 feet while the 2002- 2003 rate is 2.47 feet. The well hydrographs contained in the long-term hydrograph section as well as the shorter -term hydrographs for each well show the water level trends throughout the basin. Based on previous work, the overall decline of 2.47 feet indicates that approximately 2,223,000 acre-feet have been removed from storage. A decline of one foot is equal to a depletion from storage of approximately 900,000 acre-feet. Over the past five years (1998 to 2003) the basin -wide water level has declined approximately 5.93 feet representing a depletion of approximately 5,373,000 acre-feet or over five percent of the estimated 1965 storage in the aquifer. The depletion for the past ten years (1993 to 2003) indicates that over 8,460,000 acre- feet have been removed from storage (decline of 9.4 feet). This equates to a rate depletion of a little over one half percent per year. The original basin designation allowed for a depletion of 40 percent in 25 years. This was amended in 1990 to allow a depletion of 40 percent in 100 years. At the 10 -year average rate, the basin is being depleted at the rate of 50 percent in 100 years. This figure is somewhat misleading in that some areas in the basin are experiencing much higher rates of depletion due to a lesser saturated thickness and the fact that 2000 and 2003 were extremely dry years.