LAJU INFILTRASI MENGGUNAKAN METODE HORTON DI SUB DAS LAMBAGU DESA WOMBO KALONGGO KABUPATEN DONGGALA

ABSTRACT
The Lambagu Sub-Watershed is an area facing hydrological issues in the form of potential waterlogging and flooding due to the soil’s low water absorption capacity. This condition is influenced by the physical characteristics of the soil, particularly soil porosity, which is related to its infiltration capacity. From a regional geological perspective, the study area is part of the Celebes Sarasin Molasse Formation, which consists of conglomerate, sandstone, siltstone, and clay—rock types that influence the soil’s ability to absorb water as well as the potential for surface runoff. This study aims to analyze infiltration rates using the Horton method and to determine
the relationship between infiltration rates and soil porosity in the Lambagu Sub-Watershed.The study was conducted at several observation points representing different land uses. Infiltration measurements were performed using the Horton method through analysis of the initial infiltration capacity (f?), constant infiltration capacity (fc), and the infiltration decline constant (k). Additionally, soil porosity tests were conducted to determine the soil’s ability to store and release water. The data were analyzed descriptively and quantitatively. The results of the study show that the infiltration rate falls into the moderately fast to very fast range, with the highest value of 30.61 cm/hour on residential land and the lowest of 11.06 cm/hour on plantation land. The distribution of infiltration is dominated by the fast class at 89.47% (22.57 ha), thereby reducing surface runoff and the risk of flooding. High soil porosity (69.0%–74.0%) resulted in infiltration rates of 269.17–306.14 mm/hour, while low porosity (34.2%) resulted in an infiltration rate of 110.62 mm/hour.

Keywords: Infiltration, Horton Method, Soil porosity, Lambagu Sub-Watershed