Administration of Surface Water and Groundwater Within Colorado with the Assistance of Modeling Part 1

The implementation of groundwater administration for the Rio Grande basin within Colorado has been an ongoing and complicated effort. Starting in 1969, the State Engineer was given authority to administer groundwater use throughout the state. Early efforts to promulgate groundwater rules and regulations within Division 3 (Rio Grande basin) were not successful. Subsequent projects were implemented to provide water supplies to mitigate the effects of groundwater use (Closed Basin Project) and to collect data and build tools to better understand the impacts of groundwater use within the basin (Rio Grande Decision Support System). The severe drought of 2002 prompted the Colorado Legislature to renew the efforts of the State Engineer to promulgate groundwater rules and regulations and administer groundwater use within Division 3 (Senate Bill 04-222). The State Engineer’s efforts to administer groundwater use in Division 3 include promulgation of Confined Aquifer New Use Rules (2004), Water Measurement Rules (2005), and Ground Water Use Rules (to be promulgated in 2014). The upcoming Ground Water Use Rules will provide guidance on the quantification of stream depletions, define aquifer sustainability, and provide the ability for community-based approaches to replace stream depletions and maintain aquifer sustainability through the formation of subdistricts. The complex hydrogeologic aquifer-stream system within Division 3 required a system of models to be created, including a MODFLOW model, to quantify stream depletions from groundwater operations. The existing court decrees and the proposed rules and regulations require that the modeling be updated and enhanced as new data becomes available. Recent efforts include the incorporation of metered pumping records, refinement of the hydrogeology based on field investigations, and the incorporation of a monthly transient calibration process to accurately simulate observed data within small drainage basins within Division 3.