ANALYSIS OF DROUGHT-ENDING CONDITIONS IN THE BARTON SPRINGS SEGMENT OF THE EDWARDS AQUIFER, CENTRAL TEXAS

The amount of rainfall needed to end a groundwater drought in the Barton Springs Segment of the Edwards aquifer is dependent on soil moisture conditions and the location of rain within the contributing and recharge areas of the aquifer. Owing to endangered species and the large number of people that depend on the aquifer as their sole source of water, there is a need to better understand the relationship between groundwater drought and precipitation. Depending on drought stage, permitted groundwater users are subject to varying levels of curtailment of groundwater extraction.

The aquifer has a complex structure and hydrology due to Miocene faulting and subsequent karstification. Most recharge to the aquifer occurs through karst features in the beds of major creeks that flow ephemerally after sufficiently wet conditions. During extended drought, soil moisture deficits and increased evapotranspiration potential often keep even very large isolated storms from generating enough runoff to cause creeks to flow. However, during wetter periods small rains may yield substantial amounts and duration of flow in the creeks. The response of the aquifer system to precipitation is highly dependent on the spatial and temporal distribution and magnitude of rain over the aquifer’s recharge area and the catchment area of the creeks, as well as antecedent soil moisture conditions.

In this study, storm characteristics such as total rainfall, duration, and spatial and temporal proximity of precipitation events to each other are analyzed for the 2006, 2009, 2011, and 2013 exits from drought. Also analyzed are hydrographs of groundwater drought indicators such as wells and springs. These recent drought cycles are studied in the larger context of multi-year drought cycles and compared to the Drought of Record of the 1950s, during which the aquifer’s main spring outlet reached its lowest recorded discharge. Preliminary analysis of the datasets indicates that soil moisture is an exceedingly important parameter, and its influence on aquifer recharge must be better understood.