Academic Affiliation: Gustavus Adolphus College
Brittney Johnson is a senior undergraduate student at Gustavus Adolphus College, studying Geology and Environmental Studies. Brittney’s interest in geology grew after a homestay on the Navajo Nation. Brittney is interested in all things related to the earth. Some of her specific interests include cave systems and climate change. As an intern, Brittney focused on the impacts of extreme precipitation in the subsurface. She modeled the flow transient precipitation through the subsurface at Gordon Gulch using Hydrus 1-D.
Impacts of Extreme Precipitation on Water in the Subsurface
Increasing demands on groundwater resources raise the importance of understanding and accurately predicting current and future recharge. The predictions of recharge are complicated by the poorly understood influence of varying and extreme precipitation on the vadose zone. There is little information in the literature concerning the impacts of varying precipitation and extreme precipitation events on infiltration through the subsurface. The goal of this study is to examine the response of homogeneous and heterogeneous soils in the vadose zone to varying precipitation intensities. We focused on a small drainage basin, called Gordon Gulch, located on the Colorado Front Range within the greater Boulder Creek Watershed. We analyze a time series of precipitation and soil moisture changes at three sites in Gordon Gulch: a hilltop, slope, and valley. We use a double-ring infiltrometer to examine the infiltration rates of each respective field site. We then employ three soil cases to simulate 150-days of transient precipitation through the vadose zone using a one-dimensional subsurface flow model, HYDRUS – 1D. The hydraulic conductivity values for model input were obtained from a permeameter test of soil samples collected at the hilltop, valley, and slope. Modeled soil water storage agrees with observed general patterns of soil moisture. Model results additionally indicate that homogeneous soils can store more than double the amount of water of heterogeneous soils. Findings from this study will enhance our understanding of how the vadose zone water storage is influenced by extreme precipitation events.