Assessment of Irrigation Water Availability and Demand Using the F.J. Mock Method
DOI:
https://doi.org/10.58524/ijhes.v5i3.1455Abstract
Reliable assessment of water availability relative to irrigation demand is essential for irrigation rehabilitation planning, particularly in systems where infrastructure deterioration may reduce operational flexibility during low-flow periods. This study assessed irrigation water availability and demand in the Bekoh Irrigation Area, Ngawi Regency, East Java, Indonesia, which serves a command area of 1,921 ha. Water availability was estimated using the F.J. Mock rainfall–runoff method based on rainfall records from five stations for 2016–2025 and climatological data for 2021–2025. The analysis was conducted at a ten-day temporal resolution, and the 80% dependable discharge (Q80) was adopted as the basis for irrigation water-availability assessment. Irrigation demand was calculated for a Rice I–Rice II–Secondary Crops cropping pattern by considering land preparation, crop evapotranspiration, percolation, effective rainfall, water-layer replacement, irrigation efficiency, and planted area. The calculated Q80 discharge ranged from approximately 0.27 to 3.05 m³/s, while the maximum irrigation demand reached approximately 1.153 m³/s. The resulting water balance was generally positive; however, several ten-day periods showed very small or zero margins, particularly during parts of the late dry season, indicating that water availability should not be interpreted as a secure year-round surplus. The contribution of this study is therefore not limited to conventional water-balance estimation, but extends to identifying hydrologically critical periods that can support cropping-schedule evaluation and prioritization of irrigation rehabilitation and operational management. Because observed discharge data were not available for calibration and validation, the F.J. Mock discharge results are treated as model-based preliminary estimates rather than fully validated streamflow. Under the adopted hydrological, cropping-calendar, and irrigation-efficiency assumptions, the proposed cropping pattern may be supported, although field implementation requires discharge monitoring and evaluation of actual conveyance losses.
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