AQUIFER STORAGE - OPPORTUNITIES IN THE LOST CREEK BASIN, COLORADO

Population growth, significant increase in urbanization, over-appropriated surface water systems, and periodic drought cycles have raised concerns regarding the sustainability of water supplies in Colorado. The population of the South Platte River Basin is expected to double by 2050, resulting in a supply shortfall of approximately 120,000 acre-feet (AF). Additional storage is one of the primary management strategies to address this shortfall. The benefit and potential of storing water underground in alluvial aquifer systems is tremendous.

Water users in the Lost Creek basin, a paleo-tributary channel of the South Platte River, are heavily reliant on groundwater. The primary goal of this study is to quantify the existing groundwater reservoir and additional available storage capacity in the Lost Creek alluvial aquifer and identify potential sites for aquifer recharge and storage implementation. The alluvial aquifer is characterized by a major north-south trending channel incised into the underlying bedrock. The greatest accumulation of alluvial material follows the channel axis where its thickness can exceed 180 feet. Spring 2010 water levels range from close to ground surface in the north to over 120 feet below ground surface in the south-central portions of the basin, and are similar to historic low-level conditions in the early 1970s.

As much as 120 feet of saturated alluvial aquifer material underlies the northern part of the basin reducing to between 60 and 80 feet further south. The Lost Creek alluvial aquifer currently holds an estimated 928,000 AF of water in storage, using a uniform specific yield of 17%. Groundwater withdrawal during the period 1993 to 2010, in just a portion of the basin, has exceeded recharge by about 5,700 acre-feet/year resulting in a storage loss of nearly 100,000 AF. The unsaturated portion of the aquifer provides the reservoir for additional storage. As of Spring 2010, an estimated 1.2 million AF of unsaturated pore volume exists at depths greater than 10 feet below ground surface. Historic observations and artificial recharge tests indicate effective recharge of the alluvial aquifer is possible using surface spreading techniques. Areas in the southern and central basin represent areas of high potential for implementation of aquifer recharge and storage projects.