CS(AR)-214 : Measurement of surface-soil hydraulic properties for Ghataprabha command area

Abstract

Study about the soil moisture in the unsaturated or vadose zone is important for vegetation growth and ecosystem. This zone is the link between surface and underground hydrologic processes. It also controls the amount of precipitation that enters the soil or remain on the surface. So, to quantitatively predict the movement of water through variably saturated soils, it is required to have detailed knowledge of the the hydraulic properties of the soil. Major hydraulic soil properties to be evaluated at the soil surface are particle size distribution, infiltration rate, hydraulic conductivity, soil moisture and its retention capacity.

This report presents the results of experimental studies conducted to estimate surface soil properties for Ghataprabha command area which lies in Belgaum and Bijapur districts of Karnataka. Field experiments were conducted using double ring infiltrometer to estimate infiltration rate and Guelph permeameter to estimate hydraulic conductivity. Laboratory tests were carried out for texture analysis and pressure plate apparatus is used to get the soil moisture retention curve.

From the texture analysis, it is found that the soil is well sorted over the region. Coarser sediments are distributed for most of the area. Sorting coefficient indicates that the sediments are not insitu, but are transported through geological and hydrological processes. Retention capacity shows an increasing trend with silt and clay content. Hydraulic conductivity values for the study area are very low and at few places, the values are out of possible range to be computed by the Guelph permeameter. Infiltration results indicate a wide variation in values spatially, possibly due to the type of soils, man's influences, etc. Final infiltration rate shows a decreasing trend with the percentage of silt and clay.