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UNESCO-IHE Institute for Water Education, Delft (2008)

Schemes water balance and GIS application of land suitability for surface irrigation : case study of Bilate river basin, Rift valley, southern Ethiopia

Hailemariam, T.T

Titre : Schemes water balance and GIS application of land suitability for surface irrigation : case study of Bilate river basin, Rift valley, southern Ethiopia

Auteur : Hailemariam, T.T

Etablissement de soutenance : UNESCO-IHE Institute for Water Education, Delft

Grade : Master of Science (MS) 2008

Résumé
Irrigation land suitability analysis is a prerequisite to achieve optimum utilization of the available land resources for sustainable agricultural production. The Food and Agricultural Organization recommended an approach for land suitability evaluation for crops in terms of suitability ratings from highly suitable to not suitable, based on climatic and terrain data and soil properties crop-wise. The assignment of a given area element to suitability class is encountered with problems due to the variation of soil properties within the area as well as matching of the soil properties with more than one suitability class to different extent. The evaluation of the spatial variability of relevant terrain parameters has been carried out in a geographic information system GIS environment while assigning the land suitability for irrigation in the study area of Bilate River Basin. Three parameters (land use, soil type and topography) were considered and a suitability analysis has been carried out by using Arc Gis with Overlay-Weighted Overlay. The Digital Elevation Model (DEM) 90 m of the Bilate River Basin has been downloaded from the NASA website and was processed for further application. Theland use and the soil raster map of Bilate River Basin were extracted from soil and land use maps of the country, as produced by the Agricultural and Rural Development Ministry in 2004. There are about 12 and 10 types of land use and soils in Bilate RiverBasin, respectively. Based on their similarity the land use variables were reclassified into four major convenient classes (i.e. open shrub land, open grass land, and dense shrub land as group one ; dense wood land, riparian wood land and dense mixed high forest as group two ; moderately cultivated, perennial land cultivated, and state farm as group three ; water body, perennial swamp and perennial marsh areas as group four). The water balance of eight irrigation schemes (six existing and two additional irrigation project for which the design document is ready for implementation) have also been carried out. During computation, three scenarios were developed. Assessment of schemes water balance and river flow relations reveals that under run-off river the schemes the available river water during the main irrigation season and effective rainfall in the basin is not sufficient to supply the crop water requirement for all irrigated agriculture in the basin. On the contrary, plenty of water is available in the river during July - October and 70% of the annual flow of Bilate River occurs in these months. The study shows that there is a substantial amount of water in the river and existing irrigation schemes are using insignificant amount of water (2.7% and 4.1% ofthe available water based on Bilate Tena and Alaba Kulito Gauging Stations, respectively) from the available water resource. Storing of this water to be used in the dry season makes sense. Current crop production and food requirement of the population living in Bilate River Basin were compared. The study reveals that the current crop production in the basin cannot meet the food requirement of the population that resides in the basin and the production trend shows that it is impossible to cope with the rapidly growing population. The need of expanding the irrigation schemes in the basin and increasing the yield per ha is unquestionable. Furrow irrigation management practice of Abaya State Farm was evaluated and an alternative management practice was developed. The analysis is based on field measured data, on stream size (3 l/s) and cut off time (3 hrs), advance and recession times. The simulation model WinSRFR2.1 has been utilized to evaluate the current performance of the furrow irrigation and to give some alternatives. The most widely used modified Kostiakov formula was used to estimate the soil infiltration parameters. The result of the simulation reveals that the current application efficiency is 25.5%.Combinations of different values of furrow inflow and cut off times have been simulated. The simulation result proves that the best combinations of stream size and cut of time, which gives the highest application efficiency is 2 l/s with 1.5 hrs (76.3%) and 1.5 l/s with 2 hrs (74.2%).

Sujets  : water balance ; GIS ; crop production ; furrow irrigation ; Ethiopia

Présentation

Page publiée le 7 janvier 2017, mise à jour le 14 octobre 2018