Soil Textures-Based Evaluation of Horton and Philip's Infiltration Models for Equatorial Small Watersheds

The global database underscores Indonesia's scant 0.47% global contribution, of which 7.7% is from humid tropical climates. However, existing infiltration studies have primarily focused on specific soil textures and limited research points, resulting in a lack of comprehensive data. This knowledge gap is particularly evident in the Papua region of Indonesia, which boasts many small watersheds with abundant water resources but limited hydrologic data, especially regarding infiltration rates. Previous studies indicated that Horton and Philip's models excelled in equatorial regions but were limited in the number of soil textures and watersheds analysed or focused mainly on larger watersheds. Therefore, this study aimed to address this research gap by conducting a comprehensive analysis of the performance of the Horton and Philip's models across different soil textures in small watersheds, using the Hydrologic Soil Group classification as a reference. A performance analysis was conducted to assess Horton and Philip's performance using the Moriasi technique (based on R, RSR, and NSE best values). Field observations were conducted at 95 points in eleven small watersheds in Papua as representatives of equatorial small watersheds globally. Observations were suspended for 48 hours if rainfall occurred; thus, ten months were needed to finish the observation. The results of this study demonstrated that the Horton model performed exceptionally well for six of nine soil textures, whereas the Philip's model showed excellent performance for five out of nine. The obtained research results were compared with similar studies from Ghana, Nigeria, and India, reinforcing the conclusion that globally, the Horton and Philip's model effectively describes infiltration rates in equatorial small watersheds. Further research was recommended in equatorial small watersheds with sand and loamy sand soil textures, two of the nine soil textures that were not covered in the conducted study.