Some examples of ephemeral gully erosion in an Atlantic area of NW Spain

Abstract

This study aimed to describe types of ephemeral gullies and to determine their origin, evolution and importance as sediment sources in Galicia (Northwest Spain). Concentrated erosion was surveyed on medium textured soils, developed over basic schist of the Ordenes Complex series (Corunna province, Spain) from 1997 to 2006. The studied region has a humid Atlantic climate with a mean annual rainfall of about 1000-1500 mm. Precipitation distribution is uneven, with a maximum between October and March and a minimum in the summer. The geological materials of the study area consist of basic metamorphic rocks and granite. Gullies formed within the field where runoff starts, gullies collecting the runoff from an upstream area and discontinuity gullies due to abrupt slope changes were identified (Valcárcel, M. et al., 2003). Ephemeral gullies formed by incision along linear elements generally showed large sections in zones with high slope, so that a gradual decrease from the maximun crosssection, both toward the head and downstream, occurred. This variation from head-cut to outlet of the gully may be attributed to the small flow rates at the upstream and saturation of the transport capacity downslope, where sedimentation initiates (Casalí et al, 1999).