DETECTING ILLUVIAL LAMELLAE IN FINE SAND USING GROUND-PENETRATING RADAR

Experimental evidence has shown that soil layering can significantly a ffect water and contaminant transport, In some sandy soils, illuvial p rocesses may produce thin layers known as lamellae. Because the distri bution of lamellae is complex and difficult to determine, their effect on lateral movement and funnelling of soil water is unknown, Ground-p enetrating radar (GPR) has been used to identify layering in a variety of soils, No study, however, has considered whether lamellae can be d etected with GPR. To address this question, a detailed GPR survey was conducted with a 450-MHz antenna on a fine sand with lamellae, The sur vey area measured 15 by 18 m, and GPR lines were collected at 0.5-m sp acing, Soil-water profiles were measured in seven access tubes within the plot to provide time-depth calibration, Eleven transects 2.5 or 3 m in length were excavated for comparison between soil profiles and GP R images. Water-content profiles each showed one abrupt moisture chang e, which was always associated with the thickest lamellar horizon. Thi s ''hydraulically effective'' lamella was identified most consistently with GPR because abrupt changes in water content caused the strongest GPR reflections.