Graduation Year

2024

Document Type

Dissertation

Degree

Ph.D.

Degree Name

Doctor of Philosophy (Ph.D.)

Degree Granting Department

Civil and Environmental Engineering

Major Professor

Mark Ross, Ph.D.

Committee Member

Mahmood Nachabe, Ph.D.

Committee Member

Qing Lu, Ph.D.

Committee Member

Ajit Mujumdar, Ph.D.

Committee Member

Jiangfeng Zhou, Ph.D.

Keywords

HYDRUS-1D, Vadose Zone, Wet Equilibrium, Groundwater Recharge, Storage

Abstract

Understanding and modeling the timing and magnitude of groundwater recharge fromrainfall infiltration through vadose zone percolation is important for many reasons but especially because the flux is being acted on by root zone evapotranspiration (ET) and very little of rainfall infiltration ever becomes water table recharge. This study elaborates on the considerable time of the wetting front arrival and ultimate bulk recharge of rainfall infiltration in shallow water table fine-sandy soils typical of coastal plain environments such as Florida. Calibrated Hydrus-1D modeling of Florida (Myakka) soil was evaluated at varying depths of water table and hydraulic conductivities to bracket the timing of arrival of the wetting front and bulk fluxes. Useful normalized timing parameters are defined. In addition, this research further quantifies the concept of “wet equilibrium,” and the considerable vadose zone storage potential over and above hydrostatic pressure equilibrium that must be overcome to achieve any significant water table recharge in typical seasonal hydrologic timescales. Results indicate recharge timescales for water table depths of 1m are approximately 1 day but are considerably longer for 2 m (2 weeks), 3 m (1 month) and 4m (50 days) conditions. Given that daily vadose zone potential ET demand can exceed 0.5 cm/day in this environment, estimating recharge from rainfall infiltration is likely unreliable unless this timescale and plant root zone uptake processes are properly modeled in surface-groundwater models.

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