Effects of Initial Abstraction Ratio in SCS-CN Method on Modeling the Impacts of Urbanization on Peak Flows

Abstract

The initial abstraction ratio (λ) used in the SCS-CN method plays an important role in calculation of runoff volume and consequently hydrograph peak. The recommended value for λ in the SCS handbook is 0.2. However, recent studies suggest that λ varies between 0.05 and 0.2, closer to the lower bound. Yet, the SCS recommended value of 0.2 is still being widely used in many hydrologic models. In this study, we explored the effects of variation in λ on simulating urbanization impacts in a coastal Alabama watershed with HEC-HMS. The potential impacts of future development scenarios on peak flows were scrutinized for λ values of 0.2 and 0.05. Results showed that the use of λ = 0.05 provides superior results when model generated hydrographs and peak flows were compared to observed counterparts.

Thermal Pollution Mitigation in Cold Water Stream Watersheds Using Bioretention

“…Noori et al . () and others have discovered that this ratio more accurately predicts runoff from urbanized watersheds than the traditional λ = 0.2 that is used for small agricultural watersheds. Substituting those values into the initial abstraction equation (Equation ), it is determined that I a = 0.01 inches (0.03 cm).…”

Estimation of Initial Abstraction for Hydrological Modeling Based on Global Land Data Assimilation System–Simulated Datasets

“…Hawkins et al (2002) suggested that Ia/S is not a constant value; rather, it varies between different storms and different basins. Noori et al (2012) found that Ia/S 5 0.05 provides superior results compared to the recommended value of 0.2. Fu et al (2011) analyzed 757 rainfall-runoff events in Shaanxi and Gansu Provinces to quantify the Ia/S, indicating that the average value of Ia/S is 0.08 and the median value is 0.05 in the Loess Plateau of China.…”

“…3) Storms satisfying P/S # 0.456 should be excluded and considered as small storms for SCS-CN application (Hawkins et al 1985). The use of smaller events could bias the results toward a larger CN (Woodward et al 2003;Hawkins et al 2009;Noori et al 2012), yet low rainfall events with a high CN bias can be found in essentially every dataset (Mishra et al 2007). This criterion, namely, storms satisfying P/S .…”

“…Therefore, according to the definition of Ia and the analysis of a large amount of rainfall-runoff event data, the Soil Conservation Service recommends that Ia should be taken as 0.2 times the potential maximum retention S of the watershed, or, in other words, the initial abstraction ratio (l 5 Ia/S) is 0.2. Nevertheless, this assumption has recently been challenged (Hawkins et al 2002;Woodward et al 2003;Shi et al 2009;Fu et al 2011;Noori et al 2012;Hawkins et al 2019). The Ia/S value has a significant impact on the accuracy of flood prediction.…”

Drying Urban lakes: A consequence of climate change, urbanization or other anthropogenic causes? An insight from northern India

“…Using land use (2012), soil and rainfall data, the proposed model was developed, and later calibrated and validated against the observed run-off in 2010 and 2011, respectively. The calibration process also comprised modification of the value of the coefficient of initial abstraction (Bo et al, 2011;Noori, Kalin, Srivastava, & Charlene, 2012;Shi, Chen, Fang, Qin, & Cai, 2009;Yuan, Nie, Mccutcheon, & Taguas, 2014). An acceptable accuracy of 80% in the results was observed during both model calibration and validation.…”