Shallow Ground Water Mapping
The variability of rainfall in Ethiopia and the dependence of agriculture on rains hampers the production and productivity of millions of smallholder farmers and undermines other development gains. Irrigation offers a viable alternative to Ethiopia’s erratic rainfall patterns by stabilizing production, improving quality of produce, enabling farmers to produce multiple times annually, and allowing diversification into high-value crops. Accordingly, the ATA, with Radar Technologies International (RTI) and Addis Ababa University (AAU) as sub-contractors, and with financing from the AGP, launched an initiative in 2013 to identify water resources nationwide with potential for irrigation.
Shallow ground water (SGW) in particular was found to be a good option for irrigation because investments in this area are relatively simple: drilling up to 30 meters is sufficient to tap into the water sources, and simple manual or engine pumps can be used to lift the water. Conservative estimates show that SGW resources distributed throughout Ethiopia have the potential to irrigate 1.16 million hectares of land at the household level.16 Despite the immense potential of SGW resources, specific information on their geographic availability is limited, as is the capacity to develop them as irrigation sources.
Hence, partners in the SGW project began by mapping over 32,400 square kilometers in 89 woredas of the Oromia and SNNP regions using WATEX radar technology. Although the accuracy levels were 53% and the effectiveness of the technology is uncertain in areas with high soil moisture, the initial mapping yielded critical preliminary information without which detailed and downscaled SGW mapping could not be conducted. The WATEX technology identified surface and sub-surface moisture as a starting point for more accurate mapping; highlighted irrigable land with a slope of less than 4% (since a steeper slope would require more sophisticated irrigation methods); provided soil moisture and geomorphological analysis; and allowed the SGW potential that has been mapped to be developed for household irrigation.
Building on these findings, in 2016 the project has focused on upgrading WATEX outputs and testing alternative technologies to improve the original mapping results. With support from the AAU School of Earth Sciences, WATEX results were calibrated with observed data analysis to yield results that mapped SGW to 85% accuracy. These updated results were used to develop SGW atlases for the 40 woredas that had been mapped fully. The atlases were published and officially handed over to regions and key federal stakeholders. The final results of SGW mapping in 89 woredas indicate the presence of nearly three billion cubic meters of water at a depth of less than 30 meters. This could allow approximately 100,000 hectares of land to be irrigated, benefiting 376,000 households. In 90% of the pilot area, the water quality qualifies for irrigation.
Additionally, the search for reliable and cost effective methodology for SGW mapping settled on AQUATEST technology with an accuracy rate of 80.6%. Financed by the Czech Development Agency, the technology was tested in 47 woredas in Oromia and SNNP, over 20,000 square kilometers. According to the final report of this testing, over 676 million cubic meters of water is available at a depth of less than 30 meters, enough water to irrigate 21,422 hectares of land and benefit 85,689 households.
Two innovative ground water management and decision support tools have been developed to complement the mapping exercise and enhance the capacity of participating stakeholders. The first determines specifications for hand-dug wells, including the thickness of the water column required to irrigate a specific area of land and appropriate pump and well designs needed to regulate water use; the second helps to determine spacing between water wells so as to avoid depletion of ground water resources. Related apparatus introduced for the project includes Groundwater Exploration and Navigation (GENS) equipment, which has been provided to the Oromia Irrigation Development Authority and the SNNP Irrigation Construction and Scheme Administration Agency to continue exploring ground water sources. Lenovo Yoga Tablets (version two) that provide similar functions but use an external (rather than internal) GPS system shall be handed over to regions when the final AQUATEST maps are produced.
Based on information from the SGW mapping, training has been given to irrigation experts across 70 woredas on household irrigation development and management. Well-spacing has been defined (determined by the availability of water and an estimation of annual recharge rates) and wells have been drilled in 13 woredas in partnership with International Development Enterprises (iDE). A well-drilling group has been established in each woreda as a licensed business to provide ongoing services to well-users. To date, 91 shallow wells were drilled using the atlas; 78 of these are now productive, indicating an accuracy rate of nearly 85.7%.
Going forward, the SGW initiative will refine the AQUATEST report with AAU to include SGW development and management tools like drilling techniques and matching pumping rates with recharge tools. Atlases will be published for the woredas that have been mapped in full, and woreda, zonal, and regional experts will be trained on the use of the atlases as well as the Lenovo Yoga Tablets. Given the positive results obtained with the AQUATEST technology, a strategy for scale-up will be developed for SGW mapping at the national level with additional elements related to well-drilling and introduction of energy efficient, improved technologies for lifting and distributing water.