The Effects of Rainfall Intensities and Duration on SCS-CN Model Parameters under Simulated Rainfall

Abstract

The Soil Conservation Service curve number (SCS-CN) method has been widely used in rainfall-runoff modelling; however, the direct effects of rainfall intensities and duration, which are major factors in hydrological engineering design, on its parameters (initial abstraction ratio (λ) and potential maximum storage (S), the latter is transformed into curve number (CN)) have seldom been studied. In this study, we chose simulated rainfall experiments on runoff plots (30 mm/h, 180 min; 60 mm/h, 90 min; 90 mm/h, 60 min) to obtain synchronized rainfall-runoff data and calculated the parameters using general model fitting and event analysis methods every ten minutes throughout the duration. The results indicate that the parameters changed with rainfall intensities and duration. S decreased as the rainfall intensities increased. Under the same rainfall intensity, the S increased with the duration overall. The corresponding λ changed with rainfall intensities and duration, and has no obvious relationship under different rainfall intensities. Initial abstraction in the event analysis method is the same as the actual situation and we chose these parameters obtained with the event analysis method as our selected parameters. These selected parameters and the parameters obtained using Fu et al.’s method which was based on the standardized procedure in NEH-630 were evaluated by the Nash–Sutcliffe efficiency (NSE), the percentage deviation coefficient (PBIAS), and the ratio of the root mean square error to the standard deviation of measured data (RSR). The results show that the statistics for the selected parameters satisfied the evaluating standard, and have a better value, while the statistics for the parameters obtained by Fu et al.’s method declined as the rainfall intensity increased, and PBAIS was out of the standard range under 90 mm/h rainfall intensity condition. This indicates that the rainfall intensities and duration have important effects on the parameters of the model, and the parameters vary dynamically with the rainfall intensity and duration. These results could be useful for hydrological design in which engineers consider the return period (i.e., rainfall intensities and duration).

Curve number for runoff estimating in interlocking concrete pavement

“…Chin (2021) demonstrated that rainfall distribution is essential in determining the appropriate CN value across the United States Curve number for runoff estimating in interlocking concrete pavement of America territory. Our results also agree with the other study (Wang & Bi, 2020) that used a rainfall simulator at a plot scale to demonstrate the effect of rainfall intensity and duration on Q, S, CN, and λ.…”

Rainfall-Runoff Parameter Estimation from Ungauged Flat Afforested Catchments Using the NRCS-CN Method

“…For small catchments, it requires the recording of rainfall-runoff events at a high frequency. Some researchers [43] report that the runoff from catchment Q and the initial abstraction (I a ) vary according to the rainfall intensity and duration. In the event of a greater, more intense and shorter rainfall, the runoff generation time is earlier, and the infiltration is lower.…”

Catchment scale runoff time-series generation and validation using statistical models for the Continental United States

“…Despite wide applications of the CN method, some watersheds have been found to exhibit significant differences between observed and predicted runoff using the CN method ( Hawkins 2014 ; Muche et al, 2019a ). The effects of rainfall volume, intensity, and frequency ( Muche et al, 2019a ; Wang and Bi 2020 ), in addition to the seasonality of rainfall-runoff relationship could be among the contributing factors to the CN method’s low accuracy in those watersheds ( Rodríguez-Blanco et al, 2012 ). To increase the accuracy of CN generated runoff, Silveira et al (2000) incorporated automated estimation of antecedent moisture using five days of lagged rainfall.…”