A NUMERICAL TECHNIQUE FOR MODELING TRANSIENT FLOW OF WATER TO A SOIL WATER SAMPLER

Abstract

The soil water sampler is a widely used device for collecting water from the vadose zone. Previous users attempting to mathematically model the fluid flow around a sampler have treated the sampler as a prescribed potential (Dirichlet) boundary condition. Physically, the sampler is a finite volume of space in which the air pressure changes (as dictated by the gas law) as the water level rises within. This change in air pressure can be a dominant factor that controls the transient flow of water into the sampler. An important consequence of the air-pressure effect is that the volume of sample that can be collected and the radius of influence of the sampler are both functions of the void volume of the sampler. A numerical technique in the context of the integral finite different method (IFDM) is proposed to simulate the behavior of a pneumatically sealed soil water sampler that extracts water from a partially saturated soil. A detailed parametric analysis of the problem will be the subject of a future paper.