RN-6 : Hydrologic soil classification

Abstract

Hydrologic soil classification refers to a group of soil series that can be considered homogeneous in respect of soil characteristics. Hydrologic soil classification is useful for estimation of runoff. The soil characteristics of the watershed play an important role in the hydrologic soil classification. The various elements namely surface runoff, infiltration, percolation, soil moisture are influenced by the soil characteristics of the watershed which plays an important role in soil classification. The surface characteristics of the soil are defined by infiltration capacity and subsurface characteristics by percolation rate at which the water moves through the soil.

This review note gives in detail the history of soil classification system, statistical approaches which can be used for soil classification, hydrological parameters used for soil classification, soil classification based on SCS, soil classification based on All India Soil and Land Use Survey Organisation and classification of irrigation soils in Denver,U.S.A.

The main parameters for hydrologic soil classification considered in this review report are effective soil depth, soil texture in the surface and subsurface layer, clay content, soil structure, infiltration rate, soil permeability and soil drain- ability. Soil Conservation Service of the Unites States Department of Agriculture has classified the soils into four hydrologic soil groups namely Group A,B,C and Group D respectively in the increasing order of runoff potential. To use the soil classification list, it is necessary to know only the named of the soil on the watershed. To estimate the runoff the area of each soil must be known.