Percolation and transport in a sandy soil under a natural hydraulic gradient

Water Resources Research
By: , and 



Unsaturated flow and transport under a natural hydraulic gradient in a Mediterranean climate were investigated with a field tracer experiment combined with laboratory analyses and numerical modeling. Bromide was applied to the surface of a sandy soil during the dry season. During the subsequent rainy season, repeated sediment sampling tracked the movement of bromide through the profile. Analysis of data on moisture content, matric pressure, unsaturated hydraulic conductivity, bulk density, and soil texture and structure provides insights into parameterization and use of the advective‐dispersive modeling approach. Capturing the gross features of tracer and moisture movement with model simulations required an order‐of‐magnitude increase in laboratory‐measured hydraulic conductivity. Wetting curve characteristics better represented field results, calling into question the routine estimation of hydraulic characteristics based only on drying conditions. Measured increases in profile moisture exceeded cumulative precipitation in early winter, indicating that gains from dew drip can exceed losses from evapotranspiration during periods of heavy (“Tule”) fog. A single‐continuum advective‐dispersive modeling approach could not reproduce a peak of bromide that was retained near the soil surface for over 3 years. Modeling of this feature required slow exchange of solute at a transfer rate of 0.5–1 × 10−4 d−1 with an immobile volume approaching the residual moisture content.

Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Percolation and transport in a sandy soil under a natural hydraulic gradient
Series title Water Resources Research
DOI 10.1029/2005WR004061
Volume 41
Issue 10
Year Published 2005
Language English
Publisher American Geophysical Union
Contributing office(s) Toxic Substances Hydrology Program
Description W10414; 17 p.
Google Analytic Metrics Metrics page