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We have studied the morphology and the morphometric relations between alluvial fans and drainage basins in a bajada system including more than 20 coalescent fans developed since the Late Pleistocene as a result of the recent uplift of the Sierra Nevada (Betic Cordillera, Spain). Three allocycles of tectonic origin were recognised across which there is a clear evolution from debris flow to sheet flow dominated fans, in connection with a decrease in the volume of fines available in the source areas. The larger volume of accommodation space created by higher tectonic subsidence in the northern sector favoured vertical accumulation of sediment, with the appearance of less elongated fans. In the rest of the system, where subsidence is less, more elongated fans appear, with the development of incised channels and irregular distribution of sediment in depositional lobes. This involves the appearance of markedly asymmetric transverse profiles, as well as lengthy recurrence between the sedimentation events on particular sectors of the fans, where headward-eroding gullies develop. The lithology of the source area, where intensely fractured rocks are found, is responsible for an important sediment supply and a significant degree of clast sorting from the source area. Consequently, a weak longitudinal trend in particle size can be recognised, which influences the predominance of longitudinal constant-slope profiles and anomalous relations between both fan area and fan slope and their drainage areas. Recent intense tectonic activity has caused the appearance of abnormally low slopes in upper sectors of some catchments, where mass flows are trapped, and the fans present a subsequently higher proportion of sheet flows. Recent piracy phenomena can be recognised in some of the drainage basins, which indicate rejuvenation of the source area, in which case the fan presents a rapid increase in the proportion of mass flows with the development of a segmented longitudinal profile. Due to the recent nature of the processes, the morphometric relations in the fan fed by the basin affected by capture do not coincide with the other fans in the area. 0 1997 Elsevier Science B.V.

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The contamination by salt‐water intrusion affecting the coastal aquifer at Castell de Ferro (Granada, Spain) is especially influenced by the coexistence of two coastline lithological formations with highly differing transmissivity (highly karstified limestones and detrital sediments). Despite not having a very high intrusion volume (0.1–0.2 hm3/year), the aquifer does have a high saline content. In order to explain this phenomenon, we first of all modeled the ground‐water flow (MODFLOW) in the aquifer. Two models were then used for the fresh‐water/salt‐water contact: one assuming a sharp interface (BADON2) and the other taking into account density‐dependent mass transport (MOCDENSE). Our conclusion is that the high saline content of the aquifer is due to the existence of a preferential route for ground‐water flow through the karstified materials in contact with the detrital materials and the sea. The detrital materials located beside the karstified massif therefore constitute the route for only 10%‐20% of the system's total outlet to the sea, which is not enough water to wash the salts resulting from salt‐water intrusion. We also find that in this type of aquifer two‐dimensional transport models do not provide the most realistic results, since the effect in a direction transverse to the ground‐water flow of very transmissive material cannot be simulated in this type of profile. In this case, and despite its limitations, better results are obtained using the sharp interface model.