Assessment of the Water Use Efficiencies of Selected Laterals and Paddy Fields at the Upper Pampanga River Integrated Irrigation System (UPRIIS), Philippines

Abstract

Large gravity irrigation systems have been performing inefficiently implying that irrigation efficiency needs to be properly addressed if sustainable irrigation development is to be achieved. The conveyance and application efficiencies of selected laterals, farm ditches, and paddy fields at the Upper Pampanga River Integrated Irrigation System (UPRIIS) were assessed in terms of conveyance, application, and storage losses. The inflow-outflow method was used to determine the conveyance losses in selected laterals while water balance computation using ponding and tank methods was used to determine farm ditch and application losses in selected paddy fields. Results showed that conveyance losses from these canals ranged from 0.175 to 1.65 m3 /s while conveyance efficiency ranges from 41.3% to 81.0%, which has no significant difference with FAO values for adequately maintained canals. Percolation losses ranged from 1.98 to 10.12 mm/d which were significantly different with paddy fields and soil types and generally higher than NIA design percolation losses for each soil type. The measured farm ditch losses range from 0.09 to 23.87 lps/km with considerable variations attributed to the condition and maintenance of the ditches. Using both secondary data and measured losses, the average storage, conveyance, and on-farm efficiencies were computed as 93%, 60%, and 76.8% (dry), and 36.4% (wet), respectively. The system efficiency for UPRIIS using these representative values was found to be 32%, which is about the same as that of many large systems based on FAO studies. While a statistically significant assessment of the UPRIIS was not attained due to its size, quantifying and analyzing the causes of these water losses is necessary to provide measures to increase water use efficiency and help improve water management. Reduction of losses in irrigation systems improves water use efficiency thereby increasing the irrigated area and crop production