Soil erosion via preferential flow to drainage systems in clay soils

• Published in: Geoderma Vol. 76; no. 1; pp. 65 - 86
• Main Authors: Øygarden, L., Kværner, J., Jenssen, P.D.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.03.1997
• Subjects: clay; drainage; erosion; macropore; preferential flow; erosion; preferential flow; macropore; drainage; clay
• ISSN: 0016-7061; 1872-6259
• DOI: 10.1016/S0016-7061(96)00099-7

Runoff measurements from artificially levelled land showed that rates of particle erosion to the drainage system was even higher than that from surface runoff. This effect was increased by tillage whilst no tillage reduced the losses significantly. The field site soil type was a silty clay loam. Artificial levelling at the site had exposed an unstable subsoil, susceptible to cracking. Soil structures with macropores and cracks were examined to find out more about water and particle transport via preferential flow pathways. A field profile description of soil structure and CT scanning of monoliths from the plough layer, subsoil and backfill showed different density patterns and structural properties. The backfill consisted of clods and open voids with direct contact to the drainpipes. The soil down to 50 cm was cracked both vertically and horizontally and some cracks were leading into the backfill. Cracks of up to 10 mm width were found, indicating that transport of particles through them was possible. The measured field hydraulic conductivities varied over 3 orders of magnitude, indicative of a preferential flow network. Infiltration with dye tracer visually demonstrated rapid flow of water through cracks leading directly to the drainage system; with a hydraulic conductivity of 9.9 × 10 −4 m s −1 in the soil; and 5.8 × 10 −3 m s −1 in the backfill. These results indicate that particles can be eroded from the plough layer and transported both laterally and vertically, through macropores and cracks into the backfill, and then directly to drain pipes.