Abel Maia Genovez

Tentative Hydrologic Soil Classification for Tropical Soils

The Runoff Curve Number (CN) method is applied for estimating direct runoff from rainstorms. Its application is based on the selection of input “CN” from handbook tables of USA origin. The use of these tables is by default, insofar as CN determinations for various land use and soils have not been done for the local conditions. Soils are classified in four groups (A, B, C and D); from the lowest to the highest runoff potential. At this point, the most difficult task is classifying a soil because the general characteristics of the hydrologic soil groups (HSGs) do not provide objective criteria for applying the method outside the USA, mainly for regions or countries where there are highly weathered soils, such as Brazil. This happens because the criteria are mainly based on soil texture, once the steady infiltration rate data or saturated hydraulic conductivity data are not always available or obtained. Thus, after reviewing the current HSGs criteria, new ones were developed based on Brazilian soils to improve accuracy and consistency in allocating tropical soils to the appropriate group.