Design Note on Dakawa Main Canal Lining Options

The project's primary objective is to improve the efficiency and productivity of the irrigation system, while also enhancing the overall agricultural productivity of the region. The project's scope includes the design, procurement, and construction supervision for the rehabilitation of the I&D infrastructure at the DRF, as well as the construction of a new irrigation scheme at Mgongola. The DRF is a 2,000-hectare irrigation scheme that is owned by the UWAWAKUDA Cooperative Union. The scheme has a water right that permits the abstraction of 5,000 liters per second, which is sufficient for 2,500 hectares of rice cultivation. However, environmental flow requirements and other abstractions upstream and downstream of Dakawa need to be taken into account to ensure that the water availability is sufficient for the expanded command area. The current command area is 2,000 hectares, and the project aims to expand it by an additional 500 hectares, subject to the availability of sufficient water resources. The UWAWAKUDA Cooperative Union has a water right that permits the abstraction of 5,000 liters per second, which is sufficient for 2,500 hectares of rice cultivation. However, environmental flow requirements and other abstractions upstream and downstream of Dakawa need to be taken into account to ensure that the water availability is sufficient for the expanded command area. The Main Canal is an earth canal that is 3.4 kilometers long and has a trapezoidal cross-section. The canal has a longitudinal slope of 0.00012 meters per meter, which is lower than the minimum acceptable slope of 0.00013 meters per meter. The canal's condition is good, with no significant erosion damage or side slope failure. However, the canal's geometry has been affected by the movement of the heavy clay soils, resulting in a natural parabolic cross-section. The project aims to reduce seepage, prevent weed growth, decrease erosion from high velocities, reduce maintenance costs, reduce flood problems, increase the capacity to convey water, and provide safety against breaks. The project also aims to reduce the habitats suitable for the bilharzia snail vector and malaria-carrying mosquitoes. The concrete lining of the Main Canal is proposed to address the issue of excessive seepage, despite no evidence of seepage being recorded. The freeboard in the present earth canal is 400 millimeters, which is lower than the recommended freeboard of 500 millimeters. The project aims to increase the capacity of the Main Canal to serve an expanded command area of between 500 hectares and 1,000 hectares. Lining the Main Canal would enable more water to be conveyed through the same cross-section, avoiding the need to widen the earth canal, raise the embankments, and modify the bridges. Four options for lining the Main Canal were considered: no lining (Base Case), concrete panels, pre-cast concrete slabs, and concrete blocks. The option of no lining was not considered feasible due to the high maintenance costs associated with the earth canal. The lined canal is estimated to have a maintenance cost of 1% of the investment cost, while the earth canal is estimated to have a maintenance cost of 4% of the investment cost. The project aims to reduce the maintenance costs associated with the earth canal by lining the Main Canal. The lined canal is estimated to have a maintenance cost of 1% of the investment cost, while the earth canal is estimated to have a maintenance cost of 4% of the investment cost. The project also aims to reduce the need for regular grass cutting and grass maintenance, which is a significant cost associated with the earth canal. The project's implementation will be carried out in collaboration with the UWAWAKUDA Cooperative Union, the Ministry of Agriculture and Cooperatives, and other stakeholders. The project's timeline is expected to be completed within 24 months, subject to the availability of sufficient funding and resources. The project's budget is estimated to be $5 million, which will be used to cover the costs associated with the design, procurement, and construction supervision of the lined canal. The project's success will be evaluated based on the following indicators: the reduction in maintenance costs, the increase in the capacity to convey water, the reduction in flood problems, the reduction in the habitats suitable for the bilharzia snail vector and malaria-carrying mosquitoes, and the overall improvement in the agricultural productivity of the region. The project's impact will be monitored and evaluated through regular progress reports, site visits, and stakeholder engagement.