The phenomenon La Niña caused flooding in Colombia during 2010 and 2011, especially in the upper basin of the Bogota River, this natural risk has produced major property damage and a decrease in socio-economic conditions in major urban and rural centers. For that reason, this paper presents a determination of the floodplain of the lower basin of the Rio Frio in the urban area of Chia Colombia by HEC RAS. The model allowed to determine the maximum water levels reached on the floodplain of the Rio Frio as it passes through the urban area of Chia, for return periods of rainfall of 2.33, 5, 10, 25, 50 and 100 years. Finally recommendations for the planning of the municipality in terms of these areas found are made.