Hydrologic processes and geomorphic constraints on urbanization of alluvial fan slopes

The natural array of processes conveying water and sediment from arid mountain catchments, through alluvial fans, into the base level below is affected by human intervention to an extent unknown until a few years ago. Previously permeable fan terrain has now been replaced by paved impermeable surfaces whose drainage becomes problematic. This problem is intensified with the growth of the town and its building density, particularly vis a vis the smaller catchments. The high sediment yields, with typically predominant bed material components that are supplied by steep catchments, create situations difficult to manage in terms of effective economical and environmentally sensitive criteria. Within the context of the general inadequacy of structural attempts to fully control the floods emanating onto an alluvial fan, a case can be made for exercising the option of local, low-key engineering intervention in protecting fan settlements. Several aspects of the considerations involved are illustrated by examples from the town of Eilat, Southern Negev Desert, Israel, a dynamically developing international tourist resort.