Thesis Abstract of AGS Students
The Use of Spatial Information for Evaluating the Performance of Partupangan Irrigation System, Indonesia
Feri Arlius (1997)
This study aims for evaluating the performance of Partupangan Irrigation System, Indonesia with the specific purposes to describe the current water management and agricultural performance, to construct spatial database of this irrigation system, and to evaluate the spatial variations of irrigation network complexity and hydraulic performance. The evaluation was based on the target that had been set in the feasibility study.
The spatial data were digitized using ARC/INFO and IDRISI for Windows GIS packages. Rice water requirement was calculated using CROPWAT, a software developed for irrigation planning and management. Water measurement were made at 41 points along the canals to determine hydraulic performance while agricultural performances were based on 60 crop cutting samples.
Rotational water delivery system was practiced in Partupangan Irrigation System since the irrigation water was not sufficient to irrigate the whole area simultaneously, therefore this irrigation system was organized into three zones, in which each zone received irrigation water once a year. The water delivery performance of 0.31 brought the value of cropping intensity performance to 0.4.
Conveyance efficiency of 0.52, 0.55 and 0.38 for Zone 1, 2 and 3 indicated high water loss of 45 to 62 % along the irrigation canals. Overall project efficiency of 0.77, 1.04 and 1.16 in Zone 1, 2 and 3 showed that total water inflow to canal system in Zone 1 was higher than total rice water requirement.
Most of the irrigation structures in the study area were built along the primary and secondary canals, however, the efficiency of infrastructure could be categorized as good since 94 % of the existing irrigation structures were in the good condition. The canal density of Partupangan Irrigation System was 93 m/ha (83, 94 and 100 m/ha for Zone 1, 2 and 3) which was considered to be in the suitable range. However, in some tertiary blocks (TB 1, 8, 9, and 14), canals were built with the structures in exceeding of the suitable range, while TB 2, 7, 10, 12 and 15 had the value of network parameters below the suitable range. The number of irrigation structure, especially division box was found to be inadequate in all tertiary blocks.
Water delivery performance in Partupangan Irrigation System ranged from 0.27 to 0.66. Because of limited irrigation water supply the target irrigated area could not be fulfilled. The limited water availability reduced the value of irrigated area performance to 0.58. Although TB 15 had relatively high irrigated area performance of 1.05, but the performance of the other tertiary blocks were not satisfactory.
Relative water supply in Partupangan Irrigation System varied with time and location of tertiary blocks. Irrigation water was distributed inefficiently, however, most of the tertiary blocks received water in excess of the requirement except TB 3, 4 and 10. If water could be distributed efficiently more rice area could be developed. Surplus water was found to be adequate to irrigate extra 4.7, 7.2 and 4.4 ha rice area for Zone 1, 2 and 3, respectively. The irrigated area could also be expanded by improving the conveyance efficiency.
Crop cutting samples collected in the study area indicated a relative high yield performance (0.82). However, because of low irrigated area performance and only single rice cropping system was practiced, the rice production performance in the study area was far below the setting target. The tertiary block efficiency in the study area significantly contributed to the rice production performance. Better tertiary block efficiency in TB 4 resulted in higher rice production performance in Zone 1, while TB 15 achieved the highest production performance in Zone 3.
Improving the performance of irrigation system could be accomplished by increasing conveyance efficiency, re-arranging water distribution to all the tertiary blocks based on water requirement and the proper fertilizer application rate. Tertiary blocks 5, 9 and 13 in Zone 1, 2 and 3 respectively were more suitable for expanding rice area than other tertiary blocks in their zones, if surplus water would be better managed.
GIS was found to be an useful tool to assist the irrigation performance evaluation. The GIS method that was described in this study could be effectively used to integrate varieties of data, both textual and thematic ones in determining the variability of agricultural and hydraulic performances, and in visualizing the irrigation network configuration.