Exploring the biology and history of Senatorial Sink in Austin, Texas.

Senatorial Sink is one of the local sinkholes managed by Texas Cave Management Association (TCMA) and the City of Austin. This news article will explain the biology, geology, and history of Senatorial Sink.

Senatorial Sink is a large solution sinkhole with a large bowl inside which is part of the  drainage  system that exists at the base of any sinkhole of the Circle C Ranch and Circle C neighborhood. This enclosed sinkhole is located within Edwards Aquifer. Senatorial Sink is bowl shaped. The setback distance of this sink is 75 feet. (Ref: https://citeseerx.ist.psu.edu/viewdoc/download;jsessionid=F2A679B4B237FCBCAD71D8C14A0BD58E?doi=10.1.1.692.9179&rep=rep1&type=pdf)

Limestone ridge can be seen at the fence. The fence outlines the boundary of Senatorial Sink. The most common minerals in this environment, carbonates, include the common and sometimes clear mineral calcite. The limestone rocks of the Edwards Aquifer group were originally deposited about 100 million years ago when a warm, shallow sea covered central Texas. Marine life flourished.
(Ref: https://repositories.lib.utexas.edu/bitstream/handle/2152/22314/Perrone-2008.pdf?sequence=2)

Wildflower plants such as Lemon Beebalm, Purple Horsemint, Black-eyed Susan, and Brown-eyed Susan can be found growing around and outside of this sinkhole. (Ref: https://www.facebook.com/VWOKPWMA/photos/a.1431863163611964/1492649357533344/?type=3&source=57)

Horsemint has a distinctive citrus or lemony scent when the leaves are rubbed or crushed. It is very easy to grow and often forms large colonies. Bees and butterflies are attracted to this plant. Each whorl in the elongated spike is subtended by whitish or lavender, leaf-like bracts. Several stems grow from the base and are lined with pairs of lance-shaped leaves. (Ref: https://www.wildflower.org/plants/result.php?id_plant=MOCI&fbclid=IwAR1SMgdk6xVacW1MATpW2T0y7xGrfsUTMQqCpitKdxarGYaCp4ZHE9er0HU)


Here is the history of Senatorial Sink.

Senatorial Sink was formed 100 million years ago. The limestone rocks of the Edwards Aquifer were originally deposited when a warm, shallow sea covered central Texas where Marine life flourished. As the marine organisms died, their calcium carbonate shells and skeletons sank and solidified into layers of limestone. The sea level lowered and the Edwards limestone was buried and then uplifted. A sink called Senatorial Sink was formed by the collapse of what was once a much larger cave. This collapse was many years ago and now dirt has fallen into the sink. Here Live Oak Cave is a small part of the original larger cave that did not collapse and now consists of a passage that opens into a low room beside the sink. (Ref: https://repositories.lib.utexas.edu/bitstream/handle/2152/22314/Perrone-2008.pdf?sequence=2)

Live Oak Cave has been confirmed to be located inside the sink and is part of the drain as Live Oak Cave is located inside Senatorial Sink. (Ref: https://www.researchgate.net/publication/263425729_Edwards_Aquifer_hydrogeology)

Senatorial Sink was discovered by surveyors during the early development of the Circle C neighborhood in 1986. Senatorial Sink was privately owned then and located on the Circle C Ranch property. Senatorial Sink was named for the impressive live oak trees around the sinkhole area.

TCMA partnered up with local developer, Lumberman's Investment Corp., for a proposed cave preserve at the Village of Western Oaks in 1998. The preserve would include Get Down Cave, Equinox Cave, Live Oak Cave, Survey Line Cave, and Senatorial Sink. A management plan was developed for the preserve as coordinated by the City of Austin. (Ref: https://digital.lib.usf.edu/SFS0054761/00001)

However due to the lack cave management on of the part of the city and developer, it took nearly 8 years to gain full ownership, land rights, and mineral rights to the preserve. TMCA expressed an interest in owning and managing the preserve many years in advance as they had been the de facto managers for 7½ years.

Senatorial Sink was once privately owned by Mel Bilich for 4 years in a preserve once called Mel Bilich Karst Preserve and what is now Western Oaks Karst Preserve. Mel Bilich himself was responsible for the maintenance and care of this preserve. (Ref: https://www.geocaching.com/geocache/GC354B_mel-bilich-karst-preserve-cache)

However mismanagement and neglect lead Senatorial Sink to natural decay. Senatorial Sink had not been properly managed per the karst preserve obligations prior to 2005. TCMA and City of Austin would purchase this preserve from Mel Bilich by use of eminent domain in 2005. Mel Bilich willingly gave up the preserve land to City of Austin without any incident. Western Oaks Karst Preserve would open to the public in 2005.

Western Oaks Karst Preserve would open to the public in 2005. A perimeter fence was installed at the entrance by Mike Wharton in 2006. BCP staff and TCMA staff have given tours of this sinkhole during various times of the year.  

Senatorial Sink received a significant amount of rainfall in April 2010. The ceiling of the cave was dotted with water droplets. Many visitors including adults and children, got the chance to explore the entirety of this cave this sinkhole with help of BCP staff. Visitors saw how water penetrates the overlying rock and slowly enters the aquifer. (Ref: https://bseacd.org/uploads/BSEACD_AquiferBulletin_Apr2010.pdf)

BCP staff repaired the perimeter fence around Senatorial Sink in 2018 due to the sinkhole being located in the Recharge Zone of Edwards Aquifer. After the perimeter fence around Senatorial Sink was repaired, BCP staff continued to collect soft ticks from this sink in an effort to collaborate with Texas State University researchers and Baylor University researchers whom  are trying to determine more information about tick borne relapsing fever (TBRF). (Ref: https://digital.lib.usf.edu/SFS0070259/00001)

Today Senatorial Sink is located in a preserve called Western Oaks Karst Preserve with karst features such as Equinox Cave, Live Oak Cave, and Survey Line Cave. Senatorial Sink is gated as this sinkhole is located in the environmentally sensitive Edwards Aquifer. TCMA installed a perimeter fence at the entrance to restrict access. (Ref: https://www.researchgate.net/publication/263425729_Edwards_Aquifer_hydrogeology)

Senatorial Sink is located at 5401 Davis Lane, Austin, Texas, US 78749.