Geology

Biography

Biography: Bill X Hu

Abstract

Groundwater flow cycling in the Spring Creek spingshed and interaction between groundwater and seawater in the spring sub ground conduit is numerically simulated using the CFPv2, the latest research version of MODFLOW-CFP (Conduit Flow Process). Spring Creek Springs and Wakulla Spring located in a marine estuary and 11 miles inland respectively are two major groundwater discharge spots in theWoodville Karst Plain (WKP), North Florida, USA. A conceptual model for three repeating phases of groundwater flow cycle between the two springs and recharge from a major surface creek (Lost Creek) was proposed from a low rainfall period to a heavy rainfall period then back to a low rainfall period. Tracer tests and cave diving found a complex sub ground Karst conduit network connect the two springs. The flow rate, salinity and sea level at the Spring Creek Springs could significantly affect freshwater discharge and water stage at Wakulla Spring simultaneously. Based on the conceptual model, the groundwater flow model is developed using CFPv2 and calibrated by field measurements. Non-laminar flow, direct recharges in conduits, time-variable water stage at the submarine spring and flow exchange between conduits and porous medium are implemented in the numerical model. The developed numerical model is used to simulate the seawater intrusionand fresh groundwater contamination through the submarine spring’s conduit and its influence onthe inland spring discharge from June 2007 to June 2010. Simulated results of two spring’s discharges match reasonably well with measurements and quantitatively present the three-phase groundwater flow cycling. The regional flow field and relationship between inland spring and submarine spring are studied and evaluated as well in a prediction of sea level rise.