Water Harvesting and Urban Centers in Dryland Alluvial Megafans: Environmental Issues and Examples from Central Iran

Abstract

Underground and surface water harvesting systems in alluvial fans were among the very important environmental control on urban growths in drylands. Traditional underground water supply systems, known as Qanats (kareeze), were used for centuries as a very efficient method for water harvesting in arid lands of central Iran. Surface flood-water harvesting methods have also been recently applied for aquifer recharge in such environmental setting. However, climatic changes, increasing population and industrialization, during the last five decades, made that the water resources quite inadequate and a competition happened to pump out water from the shallow to deep aquifers of the alluvial-fan systems. This resulted in serious environmental problems, depending on the geographic positions of the urban areas on the fan surface. Desertification, wind erosion/deposition, water and soil salinity crisis and immigrations affected and especially concentrated in the cities and villages located in the down-fan areas. This paper, based on lessens learned from some of the implemented cases in Iran, examines the water harvesting projects in different types of alluvial megafans under arid to semi-arid environmental conditions. It is very important to consider the type of alluvial fans to apply any method for water harvesting projects. highest in the coarse sediments of the mountain front and hillsides and the lowest are in the impermeable soils of the flood-plain areas of the alluvial fan systems. There has been always an attempt to control at least part of this natural environmental system and obtain the minimal conditions, most importantly water resources and soil, for an urban growth. Traditional underground water supply systems, known as Qanats (kareeze), were used in drylands and desert