The Aba'ala spate irrigation systems, traditional and modern, have experienced different set of floodwater and sediment management problems. Despite the dire need of alternative spate irrigation system layout, operational strategy and locally maintainable structures, efforts made to manage floodwater and control sedimentation had been structural. Hence, the study was conducted to evaluate the existing flood and sediment management practices and identify alternative options for optimum management of floods and sediments in Aba'ala plain. Primary data including discharge, sediments and river cross-sections were collected through direct field measurement. Interviews and focal group discussions were also employed to understand the operational and maintenance activities. Delft3D model was used to simulate flow and sedimentation under different scenarios. For the existing condition, the model showed high sediment deposition and low flood water abstraction. The floodwater diverted is 2.1 and 1.16 Mm 3 from the traditional intake and 1.52 and 0.51 Mm 3 from the modern intake at medium and low floods respectively which is far below the required 2.8 Mm 3 of water. Under Scenario-II, the modern intake diversion capacity is improved to 5.38 and 2.36 Mm 3 at medium and low floods. However, a water level decline of 15 cm is observed at Water Resour Manage (2015) 29:833-847 the downstream traditional intake which could be a cause for conflict between upstream and downstream users. Under Scenario-III, the diversion capacity of the modern intake is increased to 6.23 and 2.67 Mm 3 at medium and low floods respectively. Moreover, no decline in water level is shown at the downstream intake.

With growing water variability and scarcity in Africa a reality, a renewed interest in spate irrigation systems, which harness water in ephemeral environments, has emerged. Spate irrigation is seen as practical solution to supplement food production and improve food security in areas where water supply is scarce or highly variable. The political will in support of the system is evident in countries like Ethiopia, where significant investment is currently underway to upgrade the system. While the potential exists, the actual contribution of spate irrigation systems to food security has, so far, not been significant. One of the major reasons is the very high sedimentation rates of canals and irrigated fields. In spate irrigation systems sediment is a double‐edged sword. Fine sediment brings fertility and makes it possible to build up well‐structured soils, while on the other hand coarser sediment reduces spate flow diversion efficiency, raises the bed level and removes fields from the irrigation command. As is the case in several other countries, the spate irrigation systems in Ethiopia that were modernized through conventional civil engineering practices, lack effective technical and operational measures that maximize the benefits of sediments. To address this particular problem, a study was conducted in the Fokisa Spate Irrigation System in Ethiopia. The study employed field observations and simulations with various one‐dimensional hydraulic models. Primarily based on the study, but also drawing from experience in other spate irrigation systems, this paper analyses the effectiveness of settling basins and canal designs with non‐uniform cross sections and varying slopes. The results indicate that settling basins are not an optimal alternative and that designing canals with non‐uniform sections and slope leads to better performance. It is concluded that the former are not applicable in spate systems. Copyright © 2011 John Wiley & Sons, Ltd.

Irrigated agriculture in the rainfall‐deficit semi‐arid lowlands of the Raya valley rely on spate systems to produce food crops. Climate and land‐cover dynamics upstream are, however, threatening runoff response reaching these spate systems. The objective of this study was thus to analyse the hydrological response of dryland catchments to changing climate and land cover in Guguf spate systems. Thirty‐six years of climate data were analysed using Mann–Kendall, Pettitt's test and linear regression methods, and time‐series land‐cover information extracted from Landsat satellite images in a remote‐sensing interface. The Soil Conservation Systems curve number method was then employed to formulate the likely impact of climate and land‐cover changes on runoff response, and trends analysed. Results showed that temperature, evapotranspiration and rainfall varied at least by 0.11°C, 15.2 mm and −5.1 mm yr−1 respectively, intensifying moisture stress. Moreover, improving vegetation cover in the highlands enhanced the water‐abstraction capacity of the soil, impeding the runoff curve number by 9.2%. Thus, the combined effects of climate induced moisture stress and land cover led water abstraction upstream has threatened runoff response at a rate of 0.23 × 106 m3 yr−1. In other words, the runoff response reaching Guguf spate systems degenerated by 7.96 × 106 m3 over 36 years. Such unusual highland–lowland hydrological linkage has therefore endangered the availability of surplus water to irrigate spate‐based farms downstream. Appropriate policies and strategies would therefore be desirable to address conflicting interests in scarce water resources in the face of climate change. © 2019 John Wiley & Sons, Ltd.

Flood‐based farming is a means of improving crop production in rain‐deficit lowlands. Such spate irrigation systems are growing in importance, although the effects of headwater hydrological deficit on downstream flood farming are lacking evidence. This study investigates the impacts of headwater hydrological deficit on the extent of spate‐irrigated agriculture in the Guguf spate system. The length of canals and area of spate‐irrigated agriculture to the right and left of the Guguf River for the 1980s and 2010s were tracked using a global positioning system and mapped in a geographic information system interface, while climate data were collected from National Meteorological Agency. Trends of selected hydroclimatic variables were analysed using linear regression and the Pettitt test. The flash floods have shrunk by 7.36 × 106 m3, as a result of which the length of canals and area of spate‐based farms declined by 1.37 km and 1540 ha, i.e. 35 and 57.5%, respectively, in only three decades. This corresponds to an average withdrawal of −44.0 ha yr‾¹. A single 1 million m3 decline in flash floods caused a 366.4 ha decline in spate‐based farms. Moreover, farm fields located next to the river course are less affected, compared to those at the tail of the scheme. If the current trend continues, there is a high risk that the remaining farms currently receiving floods may find themselves outside of the spate systems. Therefore, we suggest that flood management technologies are needed to optimize the efficiency of soil moisture in the spate system. © 2020 John Wiley & Sons, Ltd.

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