Hydrological soil classification in Sher-Umar river doab in Narmada basin – A research report by National Institute of Hydrology

The report deals with hydrological soil classification in Sher-Umar river doab in Narmada basin. The study and classification of soil has in the past been undertaken by engineers and agriculturists who have confined themselves to those soil properties and materials in which they had a special interest. The soils have also been studied by geologists, but the geological description of an area does not include the information required by soil scientists. The classification designed by soil users have tended to be of limited value to others as they were designed to serve a specific and limited purpose.

Soil classification is largely a 20^th century concept, although work in this area started in the preceding century. Numerous systems of soil classification have been developed and many are in use in various parts of the world. Hydrologic soil classification refers to a group of soil series that can be considered homogenous in respect of soil characteristics that influence the runoff.

Surface runoff, soil moisture storage and deep percolation due to infiltration from a storm are influenced by the soil characteristics of the watershed. Such response is affected by the characteristics of soils both on the surface and sub-surface horizons. Viewing the importance of hydrologic soil classification in estimation of runoff of a watershed, a model area has been taken up under the comprehensive hydrological study of a sub-basin in Narmada.

In this report, an attempt has been made on systematic determination of hydrological properties of soils, such as, infiltration rate, saturated hydraulic conductivity, soil samples and their physical properties analysis and then its classification, based on prevailing Soil Conservation Services (SCS) criteria. It is difficult to compute all hydrologic soil parameters falling in one group mentioned in the Soil Conservation Services (SCS) model. It is therefore presumed that infiltration rate is affected by other parameters i.e., effective depth of soil, clay content, soil drainability and groundwater table.

In other words, infiltration rate is considered to be derivative of other parameters. Hence, for classification of the hydrologic soil group, infiltration rate has been taken to be a guiding factor that includes overall effect of particle size, its distribution, compaction, topography along with others parameters. Thus, the hydrological soil map has been prepared for the study area, keeping in view the infiltration rates observed in the field.

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