Through an extensive study of river deposits in streams near archaeological sites, geoarcheologists have linked radical changes in sedimentation and erosion with the appearance and intensification of farming. Mabry (1992) was able to link changes in sedimentation and channel erosion with the growth ofearly agricultural villages in the Jordan Valley.
The process known to geomorphologists as ‘‘channel entrenchment’’ or ‘‘stream downcutting’’ lies in the destruction of stream beds and fertile flood plains. Rosen linked the abandonment of Early Bronze Age sites in the Shephelah region of Israel with the degradation of streams (Rosen 1997a). A similar scenario has been postulated for the abandonment of the Early Bronze Age site of Khirbet Iskander in Jordan (Long and Cordova 2003).
Silts originated from soil erosion in the upper reaches of the valleys caused numerous problems in the lowland streams of Mesopotamia. Large amounts of silts carried by streams ended up clogging river channels, forcing them to change courses, consequently creating destruction of fields. Irrigation canals collected large amounts of silts, creating the need for enormous cleaning operations every year (Adams 1981). Over the millennia the increase of silts transported by the rivers led to the advance of the Mesopotamian delta into the Persian Gulf and the formation of the marshes in southern Iraq (Sanlaville 1989).
Channel straightening and dike construction along the banks were common practices to maximize irrigation in Mesopotamia. However, in the long run such practices had adverse effects, producing unrelenting flooding and salinization (Adams 1981). A straight channel increases water flow velocity, augmenting the risk of overflow and catastrophic flooding.
World History
