Assessing the impact of geocell layers in sand on effective runoff parameters using a rainfall simulator

Urbanization has significantly altered natural hydrological processes by increasing impervious surfaces, leading to higher surface runoff volumes and elevated flood risk. Permeable pavement systems have therefore attracted increasing attention as a sustainable solution for mitigating urban runoff. This study aims to investigate and compare the performance of sand pavement without plastic geocells and with one, two, and three layers of plastic geocells in reducing runoff volume, time to runoff, runoff coefficient, time to end runoff, peak flow rate, time to peak, and the time interval between runoff initiation and runoff termination under six different rainfall intensities and two slopes using a rainfall simulator. To achieve this goal, a total of 48 laboratory tests were conducted. The results were analysed using factorial analysis and Duncan’s multiple range test in SPSS software. In addition, empirical relationships for time to runoff, runoff coefficient, time to end runoff, and peak flow rate were developed based on rainfall intensity, slope, and the number of test treatments. Finally, performance criteria including the coefficient of determination, root mean square error, and mean absolute error were evaluated. The results indicated statistically significant differences at the 5% significance level for the dependent variables time to runoff, time to end runoff, and runoff coefficient in all cases. Moreover, variations in rainfall intensity and the combined effects of rainfall intensity, slope, and treatment configuration resulted in significant differences in peak flow rate. The cumulative runoff volume obtained from the three layer geocell treatment was consistently lower than that of the other treatments under all experimental conditions, indicating that sand pavement reinforced with three geocell layers is more effective in reducing runoff than the two-layer, one-layer, and unreinforced configurations. Increasing the number of geocell layers delayed runoff initiation and reduced both the runoff coefficient and peak flow rate. However, no definitive conclusion could be drawn regarding the influence of geocell layers on the time to end runoff.