CS(AR)-35/98-99 : Soil classification of Dudhnai representative basin (Assam/Meghalaya)

Abstract

The Dudhnai sub-catchment of about 500 km² on the south bank of the river Brahmaputra has been selected for long term representative basin studies. Under this board objective, North Eastern Regional Centre undertook field investigations for classification of soils in the basin. This study aims at field and laboratory determination of soil classification properties under Dudhnai river basin.

Point infiltration tests using double ring infiltrometer were conducted at various locations (44 sites) in respect of different land use conditions. Soil samples were also collected from same infiltration testing sites. Field determination of saturated hydraulic conductivity was made using Guelph Permeameter for same site of infiltration tests. The undisturbed soil samples (from 44 locations) and disturbed soil samples (from 44 locations at 50 cm below surface) were collected and brought to the soil lab of the centre. Extensive laboratory measurements were made for each soil sample collected. Disturbed soil samples we re used for textural and consistency analysis. Percentage of sand, silt and clays were determined through sieve analysis and pipette method. Different engineering and index properties like moisture content, bulk density, dry density, sp. gravity, plastic limit, liquid limit, void ratio, saturated density, degree of saturation, uniformity coefficient, coefficient of curvature etc. were obtained for each soil sample. Soil suction was also measured using Tensiometer at field. Grain size curves were plotted and particle size distribution ranges have been identified using USDA criteria. Textural classification was identified using triangular classification system of USDA and Bureau of Indian Standards method (IS.- 1498-1970) also. Hydrologic soil groups were identified on the basis of infiltration characteristics SCS method.

The report presents a thorough soil investigation results for the Dudhnai river basin.