Designing terraces for the rainfed farming region in Iraq using the RUSLE and hydraulic principles

Abstract

The rainfed region in Iraq comprises an area of more than 5millionha of forest, grazing and farmland areas. Except the plains, the region suffers from moderate to severe water erosion due mainly to overgrazing and land mismanagement. Due to population growth and the shortage in water resources, an expansion in land used for agriculture in the region is expected. Terracing is an option when utilizing sloping land for agricultural production. A terrace design criterion was developed for the region in which terrace spacing was determined using the Revised Universal Soil Loss Equation (RUSLE); terrace channel specifications were determined using conventional hydraulic computations. Analyses showed that terracing is feasible on rolling and hilly sloping land in the high rainfall zone (seasonal rainfall >600mm) where economic crops are grown to offset the high cost of terrace construction and maintenance. In the medium and low rainfall zones (seasonal rainfall 400–600mm and 300–400mm), terracing for water erosion control is generally not needed on cultivated land less than 10% in slope where wheat and barley crops are normally grown; however, pioneer research projects are needed to assess the feasibility of terraces of the level (detention) type to conserve rain water in these two zones for a more successful rainfed farming venture.