HYDROGEOLOGY OF SPILLWAY CREEK, BELTON, TEXAS

Spillway Creek is a natural stream that acts as part of the emergency spillway for Stillhouse Hollow Reservoir and Dam. It is located within Chalk Ridge Falls park operated by the US Army Corps of Engineers and occurs in the Northern Segment of the Edwards Balcones Fault Zone (BFZ) aquifer. The Northern Segment is the least studied portion of the Edwards BFZ aquifer, yet supplies water to local communities, rural residents, and threatened salamander species. The channel of Spillway Creek consists of exposed bedrock that provides a rare continuous view of the lower portion of the Edwards formation, the entire section of the Comanche Peak formation, and the upper portion of the underlying Walnut formation confining bed. This research studied the exposures in Spillway Creek to describe hydrogeologic characteristics of the Northern Segment of the Edwards BFZ aquifer. Caves, fractures and springs were described and mapped along the channel. Fracture density combined with spring and seep discharges were used to develop a conceptual model of general aquifer characteristics which could be used for water management decisions and field parameters for water chemistry were collected to provide a baseline to use in later comparisons. The characteristics of the Northern Segment of the Edwards BFZ aquifer as exposed in Spillway Creek represent an increase in fracture density and subsequent aquifer flow capabilities from the Walnut formation upward into the Edwards formation with a dramatic increase in flow near the Edwards-Comanche Peak contact. This conceptual model can now be tested as a basis for understanding the aquifer within the region of the Northern Segment of the Edwards BFZ aquifer.