Gravel pavements, a type of permeable pavement, can mitigate the adverse impacts of urbanization on the hydrological cycle and environment in urban and rural areas. This study evaluated the performance of porous gravel pavements without (O) and with one (G1), two (G2), or three (G3) layers of plastic geocells, focusing on runoff volume reduction, time to runoff onset (TR), runoff coefficient (C), runoff end time (TER), and peak flow rate (PF). Experiments were conducted under three rainfall intensity scenarios and two slope levels using a rainfall simulator. A total of 24 laboratory-scale physical models were tested, each consisting of 15 cm of sandy loam soil overlaid with 15 cm of gravel, with geocell layers incorporated into the gravel as applicable. Data were analyzed using the factorial method and Duncan’s multiple range test in SPSS 21 software. Significant differences (p < 0.05) were observed in TR and C across all treatments. Variations in rainfall intensity and treatment type also significantly affected PF and TER. The G3 treatment consistently exhibited the lowest cumulative runoff volume, indicating superior runoff reduction compared to G2, G1, and O treatments. Additionally, increasing geocell layers delayed the onset of runoff. The G3 pavement was also more cost-effective than other treatments in terms of C and PF. However, no definitive conclusions could be drawn regarding the TER parameter.