Lateral groundwater flow and pond interactions during dry and wet years

Abstract

Groundwater and surface water are tightly coupled elements of the hydrologic cycle that have often been treated as separate entities. Future climate change modelling has predicted that hydrologic cycle changes, namely increasing drought frequency and flood-type events, are likely to occur. These events may directly impact the quality and quantity of both groundwater and surface water. Future water management policies must therefore be based on an understanding of how interactions between groundwater and surface water will change with a warming climate. The aim of this study was to model and analyze the lateral flow of groundwater and its interactions with a nearby pond in a shallow, unconsolidated, unconfined aquifer. Data were collected as part of a larger and ongoing study during the year 2012, a comparatively dry year, and 2013, a comparatively wet year. We first used ArcGIS and Visual MODFLOW Flex to create a conceptual model of the system, its soil layers, monitoring wells, and potential flow patterns. We then analyzed hydraulic head data, and calculated groundwater flow volumes using the Dupuit equation. We found that the groundwater flow direction reversed in the summer of 2012 and continued until the spring of 2013. Additonally, flow rate was greater in 2013 than 2012. The flow reversal was likely caused by higher evaporative demand during the summer months of 2012, drawing substantially more water from the pond than from the soil. The two-year timeframe was not long enough to determine whether this was a typical, yearly pattern, or was primarily due to the fact that 2012 was a particularly dry year.