Suspended sediment in rapid subsurface stormflow on a large field plot

Abstract

The occurrence of rapid movement of suspended sediment in subsurface stormflow on a large field plot in California is described. Concentrations of over 1OOOmg I-' were recorded in storms of only low to moderate intensity. The observed sediment was composed of uniformly fine-sized particles 4 to 8 pm in diameter. The mode of transport seems different from processes previously reported. Differences in sediment concentrations in different events, levels of 37Cs on the sediment, and several other types ofevidence indicate that the sediment was detached and entrained at the ground surface by raindrop impact and that the water and sediment flow occurred mainly through macropores in the soil. As conditions similar to those at the study site are not uncommon, it seems probable that the phenomenon may occur in many regions.

Dominant mechanisms for the delivery of fine sediment and phosphorus to fluvial networks draining grassland dominated headwater catchments

“…Deasy et al, 2009;Russell et al, 2001). Sub-surface particulate fluxes are likely to occur following soil pipe erosion (Verachtert et al, 2011), or detachment at the surface by raindrop impact which is subsequently delivered through soil macro-pores or sub-surface drains (Pilgrim and Huff, 1983). Although these sub-surface processes may be important during low magnitude events, as storm intensity increases, additional pathways of sediment movement become progressively important (Sayer et al, 2006), limiting the occurrence of anti-clockwise hysteresis events to low magnitude runoff events.…”

Preferential Transport of Soil Colloidal Particles: Physicochemical Effects on Particle Mobilization

“…The rapid transport of particles to depth depends on the structure of the soil, particularly on the presence of vertical continuous macropores. Pilgrim and Huff (1983), Jacobsen et al (1997), Laegdsmand et al (1999), Laubel et al (1999), and McKay et al (2000) observed rapid breakthrough of colloidal particles involving preferential flow. Pilgrim and Huff (1983) as well as Hardy et al (2000) suggested that the particles were detached at or near the soil surface by raindrop impact and that subsurface flow subsequently carried the particles primarily through soil macropores.…”

U.S. Geological Survey toxic substances hydrology program, surface-water contamination; proceedings of the technical meeting, Denver, Colorado, February 2-4, 1987

“…Pilgrim and Huff (1983) found suspendedsediment concentrations greater than 1,000 milligrams per liter in subsurface flow through soil macropores. The ability of flow into the bed to transport fine particles is an important factor in determining the vertical distribution of fine material below the active bed.…”