Rehabilitation and Expansion of Aligidir Irrigation Project, Eritrea
Client: Minister of Agriculture
Project: Rehabilitation and Expansion of Aligidir Irrigation Project
NRCE performed a study to assess the feasibility of the rehabilitation and expansion of the Aligidir Irrigation Project, a large cotton plantation in the western lowlands of Eritrea that is irrigated by water from the Gash River. The 12,000 hectare Project, originally developed in 1927, suffered from nearly three decades of neglect and damage during the Eritrean war of independence. The project also suffered from unreliable flows in the Gash River and very high sediment loads.
The Government of Eritrea (GOE) viewed the project as strategically important for economic recovery of the western lowlands, where many of the country’s refugees were to be resettled. For each of these alternatives, a feasibility-level design, cost estimate and operations study, and anticipated crop production were developed. In addition, NRCE directed a National sector review for cotton, and advised the GOE on matters involving the general management and privatization of the project.
As the prime contractor, NRCE directed the efforts of international sub-consultants on a land resources study, mapping, and health and environmental implications. NRCE directly undertook the hydrological analysis, assessment of groundwater resources, hydrological and sediment data collection, field survey and inventory of existing system, financial and economic analysis, and feasibility level design. In addition, NRCE completed the feasibility level design of a number of alternatives. The feasibility report, which was completed in December 1994, presented three alternatives for rehabilitation and expansion of the project.
For the feasibility study, NRCE inventoried and evaluated the entire existing physical system and developed a cost estimate for rehabilitating canal structures. In addition, NRCE assessed the feasibility of expanding the irrigation project using a new diversion facility combined with sediment traps and off-stream storage. To determine the feasibility of the proposed expansion, NRCE studied surface and groundwater resources, sedimentation, and water demand. As part of this program, sediment sampling and river-stage recording programs were implemented.
Topographic surveys were performed to locate the project facilities. Results from the hydrologic analyses and sedimentation study were used to perform an operation study. The result of the operation study was used in the feasibility level design of new canals, sediment traps, and off-stream storage. Canal enlargement and extensions were included in the design and cost estimate.
NRCE also performed an environmental reconnaissance study of the area. Various aspects of this assessment included potential impacts on human health, archeology, wildlife, and hydrology. NRCE prepared an economic and financial analysis, which resulted in a detailed construction cost estimate, farm budgets, and financial cash flow analysis. An implementation program was also formulated and presented to the GOE.
The design of the preferred alternative, which will expand the project to fully irrigate 12,500 hectares of land, was initiated in 1996 with the pre-design of the entire project, and the detailed design for the existing project area and area for expansion (minor works). The preliminary design activities undertaken for the major works included:
- Aerial photography and detailed mapping of the project area; necessary surveying and ground control for the contour mapping.
- Preliminary design of the new diversion weir; headworks, sediment removal facilities, supply canal, off-stream storage reservoir, and main canal.
- Dimension analysis and simulation of the river, diversion weir, and reservoir; dimensional hydrodynamic analysis and transport simulation of the sediment trap.
- Flood risk and dam-break analysis for the river and reservoir.
- Geo-technical investigations for the weir, sediment trap, canals, and reservoir site.
The preliminary design of the major works was completed in late 1998. The detailed design of the existing and expanded areas, including all field investigations, simulation of the modified main canal, and detailed design of all main, primary, and secondary canals and structures are also completed.
During the last few years, the GOE has been implementing the project as a result of the work performed by NRCE.
Final Design of the Phase I improvements was completed. This work involved the rehabilitation of existing main, primary, and secondary canals and structures downstream of the existing reservoir, the drainage network, and the roads as well as system expansion facilities. The expansion includes extending the main canal and constructing new irrigation and drainage canal systems and roads in the expansion area. The key tasks completed undertaken under final design included:
- Development of rehabilitation specifications
- Design of main canal enlargement and extension
- Design of the expanded irrigation & drainage system
- Layout and design of the primary and secondary canals and structures and of the required drainage system within the expanded area
In total, 205 construction drawings were prepared for the Phase I design of the Aligidir Irrigation Project. These drawings include general layout, standard details, plans and profiles of conveyance systems, roads, and structures. As part of the final design work, tender documents suitable for implementation of the project were developed based on the FIDIC (1992) system with the specific conditions of contract developed from input from various Ministries in Eritrea including the Ministry of Agriculture and the Ministry of Public Works, and from experience on other projects in Eritrea.