For a moment, imagine you’re not staring at the pixels of our newsletter in your inbox, but rather, a gently flowing stream with bald cypress trees hugging its limestone banks. The sun is shining, the ruby-crowned kinglets are chirping, and the occasional cricket frog vocalizes its iconic call. Welcome to Onion Creek, one of Texas’s largest creeks and one of the six major streams directly contributing water into the Edwards Aquifer and Barton Springs. In fact, Onion Creek is the primary source of water to Barton Springs, contributing 34% of the flow at times! Considering that an average of 32 million gallons flow through Barton Springs daily, Onion Creek’s contribution to the springs is far from insignificant. It goes without saying that the purity of Barton Springs is directly impacted by our protection and stewardship of Onion Creek.
A view of Onion Creek near Camp Lucy, located west of Dripping Springs.
Eager to better understand the flow directions and rates of underground water in the Edwards Aquifer, scientists have conducted many dye tracer studies. They’ve poured nontoxic dye into caves and sinkholes across the Edwards Aquifer Recharge Zone and installed charcoal dye receptors in various wells and springs to detect its movement. These studies have shown that underground water can travel approximately 20 miles from Onion Creek near Buda to Barton Springs in as little as three days — exceptionally fast for water in an aquifer! Interestingly, these dye tracer studies have also confirmed that during high flow conditions in Onion Creek (generally during heavy rainfalls in the spring and fall), the underground flow below the creek can reverse direction, going southeast towards San Marcos Springs.
Surface water in streams flows directly underground into the Edwards Aquifer through cracks, sinkholes, and caves in the Hill Country’s karst limestone formations. Antioch Cave, located in the bed of Onion Creek near Buda, is the portal through which the largest amount of water from the creek seeps into the Edwards Aquifer. Due to the Edwards Aquifer’s uniquely fast underground flow rates, most chemicals and sediments aren’t filtered out before its water emerges in springs.
