GULLY EROSION ASSOCIATED WITH THE EXPANSION OF UNTERRACED ALMOND CULTIVATION IN THE COASTAL SIERRA-DE-LUJAR, S SPAIN

Since Moorish times, the lower slopes of the Sierra de Lujar in southe rn Spain have been intensively cultivated. Despite steep slopes and th e highly erodible nature of the local micaschist/quartzite bedrock and derivative Quaternary sequences, accelerated erosion has largely been contained throughout this history by substantial, well-maintained roc k terraces. However, since 1987, European Union (EU) agricultural poli cy has been to encourage the cultivation of certain crops by subsidisi ng their expanded cultivation on a 'per hectare' basis. This has resul ted in hasty clearance of native Mediterranean matorral on sites reall y unsuitable for the local staple crop (almonds), and erosion-preventi on terraces are often absent or rudimentary. Gullying is now a very se rious problem on some of these newly cleared sites. This paper identif ies the lithological, topographic and agricultural policy controls on the consequent gully distribution, and then explores the pedological a nd hydrological controls on gully initiation on a single unterraced sl ope. Using these results alongside morphological data from gully surve ys, a gully initiation and growth model is presented. This suggests th at two types of gully are present in the area. 'Type 1' or upper-slope gullies are initiated by overland flows, which are relatively infrequ ent. By contrast, 'type 2' or slope-base gully initiation involves sat uration and collapse in fossil landslip scars in Holocene colluvium. T hese two very different morphological systems may integrate through th e terminal fan of the upslope gullies, in a manner described by Tiexei ra de Oliveira 1990. The implications of this are that in the study ar ea, sediment removal is associated with a very few highly productive s ites. Contemporary management is briefly assessed against this model o f geomorphic change in the area.