Siak River Tidal Water Potential Identification for Siak Kiri Swamp Irigation Area

Abstract The Siak Kiri Swamp Irrigation Area (DIR Siak Kiri) in Bunga Raya District, Siak Regency, utilises the Siak River water for irrigation via a pumping system. However, water quality is affected by salinity and acidity due to tidal interactions between estuarine and upstream flows. This condition increases the risk of rice farming failure due to suboptimal timing of water intake. This study examines tidal dynamics in the Siak River and their impact on water quality parameters at the DIR Siak Kiri’s pump station site. Secondary tidal data were obtained from the Geospatial Information Agency at Bengkalis Strait, and primary data were collected in one-minute intervals from a measurement station installed at the pump house’s water intake channel. Salinity was calculated through EC value conversion. Descriptive analysis was done to understand the relationship between tidal fluctuations and changes in acidity and salinity. Based on the analysis results, from April 25 to May 20, 2025, the acidity ranges from pH 4.96 to 6.67, while the salinity ranges from 24.75 to 63.25 ppm. It shows that salinity and acidity increase during ebb tide, while salinity and acidity decrease during flood tide. This finding is expected to support an irrigation water pumping strategy.