Analytical modeling of conductivity chemographs of Byrds Mill Spring

Abstract

Rhythmic springs occur when a groundwater flowpath that supplies a spring's discharge form a hydraulic siphon. The hydraulic siphon brings the spring varying fluxes of water that cycle over time. If these flows are only one flowpath in the total spring system, the influx of water from the siphon may have strong effects on water quality, but be difficult to detect in hydrograph data during spring storm response. Oscillations in electrical conductivity data were observed at Byrds Mill Spring, Pontotoc County, Oklahoma (USA). Byrds Mill Spring is the largest spring in Oklahoma by volume, and oscillations in electrical conductivity were observed during a set of extreme precipitation events in May 2015. A data logger placed at the spring's outflow recorded the electrical conductivity of the spring's oscillating between 520 uS/cm and 10 uS/cm multiple times while discharge remained steady.

A numerical tank model was developed to simulate the electrical conductivity chemograph of Byrds Mill Spring to test hypotheses about the geometry of the siphoning system. The model simplified the karst system as a tank connected to a siphoning drain and a tank connected to a non-siphoning drain joined together by mixing at a T-junction. Using this approach, the model was able to reproduce key features of the Byrds Mill Springs chemograph. The model results provide controls on where the siphon may be located and the dimensions of the siphon system.