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Hydraulic performance evaluation of the Wadi Laba spate irrigation system in Eritrea
Author(s) -
Mehari Abraham,
Depeweg Herman,
Schultz Bart
Publication year - 2005
Publication title -
irrigation and drainage
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.421
H-Index - 38
eISSN - 1531-0361
pISSN - 1531-0353
DOI - 10.1002/ird.200
Subject(s) - wadi , irrigation , water resource management , flood myth , environmental science , geography , hydrology (agriculture) , environmental planning , engineering , cartography , ecology , geotechnical engineering , archaeology , biology
Spate irrigation is a method of harvesting and managing floodwater, which is unpredictable in timing and volume. In the spate‐irrigated area of 16 000 ha in Eritrea, the farmers have for decades used brushwood and earthen diversion and distribution structures, locally known as Agims and Musghas , to harness and share the floodwater. Although these practices managed to make the systems sustainable for the past 100 years, they failed to fully mitigate the unpredictability of the floodwater and relieve the farmers from poverty. With the aim of improving living conditions, the government decided to modernize the spate irrigation systems. In 1998, the Wadi Laba (2600 ha) was selected as a pilot project, and its major Agims and Musghas were replaced by a concrete headwork and gabions. The main targets were: expanding the annually irrigated area from 1200 to 2600 ha, diverting large floods in a regulated manner so as to increase the probability of irrigating the downstream fields, while preventing erosion and sedimentation and reducing the labour and brushwood needed for operation and maintenance. Field surveys, discharge measurements, interviews and group discussions were conducted to evaluate the performance of the Wadi Laba system. It was found that in an “excellent” flood season, only 1400 ha was irrigated. Reasons include: the inappropriate design assumptions and approaches in the initial phase of the modernization, the non‐coherence of the modern design with the indigenous water rules and water‐sharing arrangements, the failures of the breaching bund, the sedimentation in the culvert and the incorrect operation and use of the scour sluice. Among the proposed improvements are: strengthening the farmers' organization technically, institutionally and legally, replacing the culvert with a head regulator gate, constructing supplementary offtakes, converting the breaching bund into a low‐crested rock fill spillway. Besides discussing these issues, this paper provides quantitative justification why the floodwater would have to be supplemented with groundwater, if there is to be a real possibility of achieving the set targets. Copyright © 2005 John Wiley & Sons, Ltd.