Colorado’s groundwater reservoirs–-An underutilized resource

The impact of climate change, particularly in the semi-arid west, has created unprecedented challenges in maintaining a reliable water supply. The water levels in the two largest reservoirs in the U.S., Lake Mead and Lake Powell, are at historic low levels. Any further declines in their capacity also jeopardizes them as the largest producers of hydroelectric power in the southwestern U.S. These reservoirs are critical components of the Colorado River Compact that dictates water deliveries and obligations of all states in the basin. As Colorado is the headwater state, reduced flows in the Colorado River will have cascading ramifications to the rest of Colorado’s water supplies. Over 80% of Colorado’s water use is sourced from surface water in seven major river basins. Consequently, reservoir storage is a critical infrastructure component in managing this resource. The west slope contains 70% of the state’s surface water though only 11% of its population. This imbalance creates greater demands for moving west slope water to the Front Range metropolitan areas. Colorado also contains vast groundwater resources in numerous and varied aquifers across the state. Groundwater is mostly used for domestic water supply and supplies water to approximately 20% of the state’s population. Colorado’s groundwater resources are a vital and an under-utilized piece of the state’s water portfolio. Sustainable development of these resources for beneficial use could relieve some pressure on the state’s river systems particularly during drought cycles. Colorado’s alluvial and sedimentary bedrock aquifers also have a tremendous capacity to store more water. Aquifers offer natural capital infrastructure with storage, transmission, and treatment capabilities. Most importantly, storing water underground avoids the massive evaporation losses inherent in surface water reservoirs. The Colorado Water Plan focuses on a measurable objective for future water storage that includes groundwater through implementation of innovative technologies such as managed aquifer recharge. The state has sponsored a number of studies that have identified tens to hundreds of thousands of acre-feet of storage capacity in various aquifers. Unfortunately, the state has only recently promulgated rules and regulations for recharge and extraction in nontributary aquifers outside of the administrative Denver Basin. While a number of metropolitan water districts are exploring or implementing aquifer storage and recovery projects in the Denver Basin, no such operations have been implemented on the western slope. The current water supply situation presents a tremendous opportunity for hydrogeologists to identify and characterize suitable aquifers throughout the state for both water supply and storage.