Water Content Wave Approach Applied to Neutron Radiographs of Finger Flow

作者：Hincapie Ingrid; Germann Peter^*

来源：Vadose Zone Journal, 2010, 9(2): 278-284.

DOI：10.2136/vzj2009.0102

Finger flow along distinct paths in homogeneous soils and other porous media is well known, but its characterization and quantification with existing approaches is challenging. Neutron radiography produces 2-d images of water content distributions that allow testing of a water content wave approach to finger flow. Neutron radiographs were taken every 25 s during finger flow in a sand box that was 200 mm wide, 400 mm deep, and 5 mm thick. The sand was sieved to 0.2- to 0.5-mm diameter. The area of finger flow was 30 mm wide. We approached water content variations during infiltration and redistribution in the finger flow area with a water content wave model that assumes gravity as the driving force and viscosity to oppose it. The two model parameters are thickness of the water film F (mu m) and its contact length L (m(-1)) per unit cross-sectional area A (m(2)) between the film and the stationary parts of the sand-water-air system. The velocity v(W) (m s(-1)) of the wetting front is an exclusive function of F, while mobile water content and volume flux density are functions of L and F. We observed constant v(W) across the entire depth of investigation, which indicates constant F despite the considerable spatial variations in bulk density and porosity. The contact length L expresses the surface area per unit volume of the medium onto which momentum dissipates. The value of L compared well with the estimated surface area per volume of the smallest sand fraction during unhampered flow; however, it increased drastically when flow was influenced by the capillary fringe at the bottom of the sand box.

• 出版日期2010-5