EVOLUTION OF GROUNDWATER MANAGEMENT RULES IN RESPONSE TO CHANGING USE OF GROUNDWATER FROM THE HIGH PLAINS (OGALLALA) AQUIFER IN TEXAS

The High Plains aquifer is an extensive (>450,000 km²) unconfined aquifer that supplies most public-water supply systems and agriculture across the U.S. High Plains. The Ogallala Formation is the most ubiquitous part of the aquifer. More than 70 percent of the aquifer's extent in parts of eight states is under regulatory jurisdiction. Most states claim ownership of groundwater in the aquifer but issue permits for the withdrawal of water. Groundwater in Texas, however, is a property right that can be separated from surface rights. By Texas statute, groundwater conservation districts (GCDs) are the state's preferred method of groundwater management and 12 districts cover the most productive ~80 percent of the High Plains aquifer in the state.

GCD rules and regulations have been evolving in response to changing demand for groundwater. Many Texas GCDs with jurisdiction over the High Plains aquifer were created to control the depletion of storage in the aquifer. Historically, irrigation made up 70 to > 90 percent of the water use from the aquifer. During the past 50 yr, in some areas application rates averaged as much as ~0.15 m³/m²/yr, water levels fell by > 0.6 m/yr, and saturated thickness decreased in half. One of the GCD duties is to certify for the IRS the annual depletion of water from storage; landowners can claim a depletion tax credit for their property's decreased saturated thickness.

GCD-issued permits for irrigation-water production were traditionally limited to acreage-averaged rates of ~0.3 m³/m²/yr, greater than the average use. Municipal-water demand is projected to increase by 67 percent from 2000 through 2050 to > 8.7 km³/yr, creating and changing markets for groundwater. Application of the traditional ~0.3 m³/m²/yr irrigation-permit rate to municipal water production permits for acreages of 160 to >800 km² has challenged assumptions underlying some aquifer management plans.

Newly adopted management rules have the goal of limiting average annual rates of decline of monitored water levels to a small percent (e.g., 1.25 %) of baseline saturated thickness. Hydraulic conductivity and storativity, which impact the rate of decline of water level, have not yet been taken into account in setting monetary value to water rights in the High Plains aquifer in Texas.