Methodology

Rationale: Wells are the greatest source of groundwater depletion for the Ogallala aquifer. Well density has a direct relationship with the rate and quantity of groundwater withdrawal. Counties with high well density are likely candidates for rainwater harvesting programs. However, withdrawals from wells can be minimized if there is greater precipitation or surface water in the county. In addition, the presence of government groundwater conservation programs and interbasin transfers can reduce impacts in high well density areas.

Each of the criteria below were used to develop a suitability map indicating which ten counties should be prioritized for a rainwater harvesting program. Well density was considered negatively proportional to suitability and precipitation, surface water and governance were all considered positively proportional to suitability. The Spatial Analysis section discusses the degree of importance assigned to each factor.

Rationale: Precipitation is what replenishes the Ogallala aquifer. Overall, the rate of recharge for the aquifer is less than the rate of withdrawal, but higher precipitaion is an important offset to withdrawals. Counties with lower precipitation are more likely to require rainwater harvesting.

Rationale: Relatively little surface water percolates into the Ogallala, so it is not a major source of groundwater recharge. However, greater surface water coverage can offset groundwater withdrawals by providing an alternative water source for irrigation and domestic use. Counties with greater surface water coverage are a lower priority for rainwater harvest funding.

Rationale: Government policy and funding often affect environmental conditions. In the case of groundwater in Texas, the state has an extensive water management bureaucracy and infrastructure that includes groundwater conservation districts, priority groundwater management areas, and plans for interbasin transfers. The effectiveness of water governance is often under debate and an analysis of this parameter is beyond the scope of this project. For the purposes of this analysis it is assumed that areas with government administered groundwater conservation programs have a reducing impact on groundwater withdrawals. In addition to conservatoin areas, the state of Texas has plans for several interbasin transfers to convey surface water to dryer regions. It is also assumed that interbasin tranfers will have a reducing impact on Ogallala withdrawals effect if implemented.