SENSITIVITY OF THE FLOOD EXTENT TO THE INITIAL ABSTRACTION RATIO OF THE NRCS-CN METHOD IN AN URBAN WATERSHED

Código

XVI-ENAU_VI-SRRU0176

Autores

Ricardo Augusto de Farias Freire Filho, Abderraman Róger Amorim Brandão, Samuel Almeida Dutra Júnior, Stephanie Maria de Oliveira Lima, Ana Beatriz Laluce Vaz, Mateo Hernández Sánchez, Eduardo Mário Mendiondo

Tema

ENAU - 02 - Processos Hidrológicos Urbanos, Modelagem e Qualidade da Água

Resumo

The initial abstraction ratio (?) in the Natural Resources Conservation Service Curve Number (NRCS-CN) method directly influences the estimation of effective rainfall, but its effects on spatially explicit hydraulic outputs are still rarely discussed in urban watersheds. This study evaluated the sensitivity of water depth and flood extent simulated in the Hydrologic Engineering Center?s River Analysis System (HEC-RAS) to changes in ?, comparing the classical value of ? = 0.20 with the reduced value of ? = 0.05 in the urban Aricanduva River watershed, São Paulo, Brazil. To maintain consistency with the NRCS-CN formulation, the tabulated Curve Number (CN) was reinterpreted, reducing the representative watershed value from 85 to 76. The results indicated that reducing ?, together with CN conversion, decreased effective rainfall by 13,7% and produced spatially heterogeneous differences in water depth, mainly concentrated along the drainage network and in areas near reservoirs. Although the overall flood extent remained similar between scenarios, local differences greater than 0.50 m indicate that the choice of ? can affect the hydraulic representation of critical areas. These results reinforce the importance of evaluating ? in hydrologic-hydraulic modeling, especially in urban watersheds, where its selection may locally alter simulated water depths.