Rainfall-runoff modelling has always been of great importance in hydrology. Recently, the Event-Based Approach for Small and Ungauged Basins (EBA4SUB) model, based on the instantaneous unit hydrograph (IUH) formulation, was released. The EBA4SUB model was originally developed considering only the surface flow, and in this work it has been generalized considering also the subsurface flow. The aim is to make EBA4SUB applicable both for Hortonian and/or for Dunne-Black mechanisms, proposing the so-called Generalized EBA4SUB model (GEBA4SUB). Here, GEBA4SUB and EBA4SUB are compared at the event scale, using observed rainfall-runoff events, and in estimating design discharge, using extreme value observations. In both cases, the results suggest that GEBA4SUB could outperform EBA4SUB, with improvements from 15% to over 100%.