Rainfall Intensity Based Duration Curve Analysis with Bernard Model: Case Study in Lokoja City Environs

Abstract

Rainfall Intensity-Duration (I-D) curves are used by a wide range of professionals, including engineers, water resource managers, and urban and regional planners – to manage impacts and risks related to extreme rainfall. I-D curves are fundamental hydrological tools required for urban drainage planning, hydraulic structure design, and flood hazard estimation. They also provide the crucial statistical weather data needed to understand, predict, and mitigate the debilitating effects of rain on high-frequency radio waves, enabling the design of resilient and reliable modern wireless communication systems. For this research, intensity-duration curves were constructed for the Lokoja environs of Nigeria from the historical rainfall data applying the Bernard Model for the data processing and curve fitting. Daily rainfall records over 12 years (2008–2020) were examined to derive maximum annual intensities for durations from 1 hour up to 12 hours. The Bernard model, based on empirical frequency distribution, was employed to establish the intensity (I) versus duration (D) relationship. It was found that a strong inverse hyperbolic relationship between intensity and duration, typical of tropical rain regimes, exists. In particular, high-intensity short-duration events were found to pose the greatest danger to existing storm water infrastructure in Lokoja, vindicating the necessity for urgent upgrade according to curves which were calibrated. The resulting I-D curves are critical inputs into design for engineers working on resilience projects in the rapidly developing confluence town like Lokoja.