Abstract

FRANCISCO-NICOLAS, Néstor et al. Runoff assessment with the SCS-CN method in the subhumid tropic of Mexico. Terra Latinoam [online]. 2010, vol.28, n.1, pp.71-78. ISSN 2395-8030.

The objective of the study was to validate the numerical curves method of the Soil Conservation Service (SCS-NC) of the United States in order to predict runoff. The experiment was established on a hillside site in a Typic Tropofluvents, 14.6% slope, soil with an organic matter content of 1.4%, a 6.1 pH, and 1683 mm of rainfall as annual average. The SCS-NC method was validated using data from conventional runoff plots 2 m wide by 25 m long, on the following soil management systems: 1) living wall terraces using horse-drawn traction (LWT), 2) conservation tillage (CT), and 3) conventional tillage (COT). The numerical curve (NC) values were defined for the moisture conditions (AHC) from accumulated rainfall from the five days previous to the event as dry conditions, average conditions and wet conditions. CN calibrations were performed for the year 1996 and validation comprised the period 1997 to 2002. Efficiency of the evaluated method was assessed using the determination coefficient (R²) as well as the Nash-Sutcliffe coefficient. On average, the COT system generated the largest annual runoff, whereas in the other systems it was 50% less. The annual runoff coefficients were 15.2, 15.9, and 30.2% for LWT, CT, and COT systems, respectively. The runoff: rainfall relationship was fitted to a potential model through a R² whose value ranged between 0.61 and 0.74. The LWT system showed NC values very similar to those of CT, from 78 to 82, with the three AHC, whereas in the COT system, the NC value for the three AHC was higher in the order of 86 to 91, although NC values that contributed the most efficiency in predicting runoff were the lowest. Concluding, using surface runoff data, evidence was found to validate the use of NC information to estimate this hydrological variable in runoff plots.

Keywords : numerical curve; runoff coefficient; soil management; living wall terraces; conservation tillage.

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