The contribution of terracing for flood reduction in the urban area of Xanxerê (SC)

The urban area of the town of Xanxerê, state of Santa Catarina, Brazil, faces inundation and flooding problems that demand complex structural measures due to intense urbanization over the natural drainage network. In addition, a large part of the farmland of the rural area presents soil erosion issues and water loss, which contributes to urban inundation. This study evaluated the contribution of the terracing technique in farming areas in reducing maximum runoff in the urban area of Xanxerê, Santa Catarina. Maximum runoffs were determined by the SCS hydrograph method for projected rain and return times of 25, 50 and 100 years. Scenarios such as the present situation were considered, as well as two others, with the implementation of drainage terracing and level terracing in farmlands with annual crops and pastureland. The effect of terracing was evaluated by CN alteration in these areas. For the rural basin, the implementation of gradient terracing reduces peak runoff by about 10%. The implementation of level terracing reduces peak runoff by around 50%. On the other hand, in the entire area of the basin under study, the use of gradient terracing reduced peak runoff by about 7%, while the use of level terracing reduced peak runoff by between 25 to 32%. Results demonstrate that adopting conservationist practices in rural areas can effectively contribute to solving urban drainage problems. Keywords: erosion, soil conservation, terracing.