Part B Study Guideline - Soil Survey and Land Evaluation and Part 1-C Design guideline on hydraulic structure gates

Abstract

Ethiopia has an estimated 3.7 million hectares of irrigable land and only about 5% is currently developed. This has shown that, the contribution of the irrigation sub sector to the national e c o n om y is very low. One of the constraints restricting this development is the low national capacity in irrigation project study and design. The Ministry of Water Resources has identified this short fall and initiated the preparation of procedural Guidelines. Criteria and manuals for study of medium and small scale irrigation projects. The Soil and Land Evaluation guideline is one of the muiti disciplinary subjects prepared under this assignment. Knowledge of the soils with in a potential irrigable area is essential for economic and technical reasons. The high cost of development of irrigated agriculture requires justification by assessment of the risks and benefits; and the design of the irrigation scheme itself is dependent on detailed knowledge of the soils within the irrigable area. Soil survey and land classification are generally accepted essential preliminaries to invest in irrigation development. By carrying out a systematic soil survey, in which, all important surface and sub - surface characteristics of individual soil bodies are mapped, the findings can be used, not only for irrigation development projects, but also in the planning of many different forms of land use and management practices. Soil surveyor has to identity significant differences with in the soil body, so as to enable him demarcate those areas which for all practical use and management purposes are uniform. Moreover, soil survey should interpret the significance of the constraints mapped in terms of different combinations of irrigation methods, types of crops and cropping pattern, methods of management which seem to be physically, socially and economically relevant. Changes associated with the introduction of irrigation are generally much greater than those under rainfed agriculture, and accurate prediction requires a correspondingly wider and soimder knowledge of the soils and substrata. Site characteristics such as topography, land use land cover, vegetation, stones, flooding, termite mounds and other surface feature are very important aspects in considering the feasibility of irrigation development, since they influence the cost and/or physical possibility of land improvement. Knowledge of soil physical characteristics helps to create a favorable environment for plant growth and crop production. Acquisition of chemical data provides awareness about plant nutrient availability which helps in efficient fertilizer management. All the above soil data will be used in soil and land classification in which relatively uniform management is possible to adopt. Irrigation planning requires a high degree of precision of soil boundary location, while the accuracy of economic studies required to attract capital from international investment agencies, necessitates fairly detailed knowledge of the distribution of different kinds of soils, their suitability for irrigated agriculture and then land development requirements and limitations, in all command areas. Precision in soil type and soil boundaries is related to mapping scale, the density of soil observations, sampling for laboratory analysis, filed testing on really representative sites. This guidelines will discuss each of the above under the different chapters here in under.