CHARACTERIZING DISCHARGE SIGNALS AND FLOW MECHANISMS AT A VIRGINIA EBB AND FLOW KARST SPRING

Karstic ebb and flow springs are relatively uncommon phenomena that have been the subject of interest for millennia. These springs exhibit unusual discharge patterns which are related to the properties of, and mechanisms functioning within, a karstic conduit system feeding the spring. Other than diurnal effects, ebb and flow signals are generally unrelated to environmental conditions, though these conditions may influence the periodicity of an ebb and flow signal or switch it on or off during periods when discharge is too high or low for the triggering mechanism to function. Identifying and characterizing ebb and flow discharge signals, and the mechanisms which produce them, can be challenging. Other researchers have recognized and modeled several different mechanisms which are capable of producing an ebb and flow or periodic signal.

We have instrumented an ebb and flow karst spring in Virginia where we are recording discharge and temperature data at one-minute intervals. Time series analyses of these data reveal several different ebb and flow signals, with at least 2 being truly periodic. Different mechanisms for producing these signals are presented and compared with published data and results from other ebb and flow springs documented around the world. The spring we are studying appears to be even more unusual than most in that there are multiple mechanisms causing different ebb and flow and periodic discharge signals. Thus far, we have identified at least four distinct signals. Additionally, multiple signals are observed to overlap at certain discharge rates.