Soil and water management in spate irrigation systems in Eritrea

Spate irrigation has been practised over 100 years in the Red Sea coastal zone of Eritrea such as the Sheeb area. Main problem of the spate irrigation system is water shortage caused by irregular rainfall in the highlands of Eritrea and breaching of the irrigation structures by destructive big floods. Annually, a tremendous amount of soil with nutrients is eroded from the adjacent highlands, transported by seasonal streams (wadis) and deposited on the lowlands in the irrigated fields. The dominant types of soils of Sheeb area are the Fluvisols, which have good physical and chemical properties. The annual sedimentation on the spate fields enables the farmers to harvest a crop without application of fertilisers. A nutrient balance study revealed no soil mining in the spate fields. Farmers in Sheeb could obtain a more uniform water distribution over their fields with better levelling. Of the total area of Sheeb (8,000 ha), about 3,160 ha of land was classified as highly and moderately suitable for spate irrigation. When the flood diversion structures (at wadis Laba and Maiule) are made more permanent, an additional 2, 000 ha of land can be irrigated. In general, spate irrigation production system is a 'cost effective' system if the irrigation structures are properly maintained at low cost and if the fields receive enough water and nutrients.