Grantee Research Project Results
Modeling of Salt Accumulation in Unsaturated Vertical Fractures in Arid Regions Subject to High Evaporative PotentialsEPA Grant Number: U915891
Title: Modeling of Salt Accumulation in Unsaturated Vertical Fractures in Arid Regions Subject to High Evaporative Potentials
Investigators: Burns, Erick R.
Institution: Oregon State University
EPA Project Officer: Boddie, Georgette
Project Period: January 1, 2001 through January 1, 2004
Project Amount: $92,725
RFA: STAR Graduate Fellowships (2001)
Research Category: Fellowship - Geology , Academic Fellowships , Ecological Indicators/Assessment/Restoration
Groundwater aquifers are the major, and sometimes only, water supply in semiarid regions. Because rainfall in arid regions is typified by strong seasonality during which storms may be of very high intensity, fractures and other macropore systems are known to play a major role in groundwater recharge. In many arid regions, salt crust formation is common both on the ground surface and inside macropores. Formation of these crusts is the result of extended periods of time during which the evaporation potential far exceeds the annual rainfall, and is attributed to evaporation, wetting and drying cycles, and soil capillarity. Salts washed from the ground surface and from the walls of macropores during recharge events are carried rapidly towards groundwater. Because the salts are concentrated in these areas, a disproportionately high volume of salts is added to the groundwater relative to the amount of rainfall. Subsequent low rainfall periods then allow the evaporative potential of the sun to draw salts back to these surfaces, again concentrating them. For these reasons, use of a bulk soil salt concentration and precipitation records may be very inadequate to predict the potential salt loading to groundwater in arid regions. The objective of this research project is to create a mathematical model to aid in analyzing the relative importance of competing processes.Approach:
Salt accumulation rates on a fracture surface, and subsequent transport to groundwater systems by episodic events is a complex process. Although the process and potential transport rates have been suggested by field observations, a mathematical model to predict the rate of formation and transport potential has not previously been formulated. The mathematical formulation of the problem will require inclusion of at least four main driving forces: evaporation, osmotic potential, capillarity, and hydraulic potential. Because these forces are not linearly dependent, the interaction of the forces will be complex. A general conservation of mass, momentum, and energy in a continuous media approach is used to derive the general governing equations. Constitutive relations are developed and adopted from the scientific literature. The resulting mathematical model will be used to analyze the relative importance of those processes identified in a series of laboratory experiments and fieldwork conducted in the Negev Desert, Israel. Furthermore, the model will be used to design future experiments.Supplemental Keywords:
fellowship, groundwater aquifers, salt accumulations, arid regions, groundwater, groundwater recharge.