REMOTE SENSING AID GIS -BASED PLANNING OF AN IRRIGATION PROJECT - A CASE STUDY

Abstract

The Geographic Information System (GIS) and Remote Sensing (RS) technology has made an incredible progress in the planning and management of the water resources. Handling and managing a large amount of spatial data is cumbersome and time con-suming. Thus, GIS can handle large amount of spatial, non spatial data and its analy- sis which assist in planning and decision making in the planning and management of the water resources. The planning of any irrigation system may be perfect when the in-depth study of the water balance of the available resources is carried out. The Evapotranspiration (ET) plays an important role in water balance studies. Accurate estimation of ET is based on the empirical equations and methods to calculate the standard crop evapotranspiration (ETo) factor. However, the result may be valid for certain areas and climatic condition of the world. Therefore, selection of a reasonable method of ET estimation is another important aspect in water balance estimation. The world is also worried about the climate change and its future impact on water re-sources. The climate change may effect the rainfall pattern, crop productivity and the whole water cycle system. Irrigation sector may be suspected area from the potential climate change. Therefore, this study aims to integrate the information derived form the satellite data, water balance estimation and trend analysis of the long term rain-fall and run-off in the context of planning of the Sikta irrigation project situated in Nepal as a case study. The trend analysis of 40 years of rainfall data shows that there is no trend in annual average rainfall in the Khajura (0409) and Naubasta (0412) stations. In the Khajura (0409) station the rainfall amount between 50 to 75 mm shows a falling trendfrom all the Kendall 's rank correlation, turning point and regression tests. The monthly aver-age rainfall of April, June, July, August, September and October months also showed no trendfrom Khajura (0409) station. The estimated annual average ETo of the study area was found to be 1311, 1372.5, 1531, 1463 and 1323 mm from the FAO Penman Monteith, Pan Evaporation, Modified Penman, Hargreave's methods and CROP WA T 8.0, respectively. The ETo values of FAO Penman Monteith method matches closely with Pan Evaporation method except for the month of May to July. The FAO Penman Monteith method yielded slightly lower (of 0.25 to 0.88 mm/day) values in comparison to Pan Evaporation method. The net command area of the Sikta irrigation project was M found to be 30,050 ha. From this study, the shortest possible main canal alignment was found to be 43.1 km. After analysing the 44 years of runoff data, the estimated annual average surface water potential of the Rapti River was found to be 3970 MCM. Analysis shows that from surface irrigation only 2505.5 MCM of water shall be available at 80 % dependable flow. The total annual irrigation water requirements considering the NCA of 30,050 ha with 242% of cropping intensity was found to be 523.1 MCM out of which 495.7 can be utilised from surface water resource as a run-off type irrigation system which is only one fifth of the 80 % dependable flow. The water deficit of 46.9 MCM during February to June can be met through the existing and future ground water development.