Analysis of Rainwater Flow in the Lower Reach of the Dua Jembatan River, Jayapura Regency

Abstract

Surface runoff plays a significant role in increasing the risk of flooding in river basins, particularly in areas with land-use changes and limited channel capacity. This study aims to analyse the characteristics of surface runoff, evaluate the stability of riverbank slopes, and assess the hydraulic capacity of the Jembatan Dua River in Jayapura Regency. The methods employed include hydrological analysis using the Nakayasu Synthetic Unit Hydrograph, land-use analysis based on spatial data, and hydraulic analysis based on channel geometry measurements and Manning's equation. The results indicate that the peak flood discharge for a 10-year return period is 0.787 m³/s, with a time to peak of approximately 1.2 hours, indicating a rapid hydrological response. Flow velocity in the river channel ranges from 1.21 to 1.86 m/s. Land-use analysis indicates a decline in forest cover and an increase in built-up areas, which contribute to increased runoff. Slope stability analysis indicates that most river banks are in a stable condition, with a Safety Factor (FoS) > 1.5, although several critical points have FoS < 1.5. Hydraulic analysis results show that the river channel capacity is unable to accommodate the 10-year return period flood discharge, thus potentially causing flooding in the downstream section.

Keywords: Surface Runoff; Channel Capacity; River Discharge; River Basin Hydrology.