Estimation of irrigation return flow in Lokapavani area of KR Sagar command in Karnataka - A research report by National Institute of Hydrology

The study deals with the estimation of hydrological soil properties of the area of Lokapavani River in KR Sagar Command in Mandya district of Karnataka. The properties determined are soil texture, porosity, saturated hydraulic conductivity, specific gravity and soil moisture characteristics.

The disturbed and undisturbed soil samples from eighteen locations along different depths were collected and analyzed. Eighty-five disturbed soil samples were used to determine the grain size distribution, porosity, specific gravity and soil moisture characteristic curves with the help of electromagnetic sieve shaker, master sizer, GeoPyc and pressure plate apparatus. Twenty undisturbed soil samples were used to determine saturated hydraulic conductivity with ICW Permeameter.

The results of the grain size distribution, porosity, specific gravity and soil moisture characteristic curves are presented in graphical and tabular forms. The textural analysis of the soil shows that there are two types of soil that extend up to 30 cm below the surface. 

The values of saturated hydraulic conductivity in the study area vary from 10.69 to 21.1 %. Wilting points lie between 5.5 to 14.5 % while available soil moisture varies from 4.45 to 10.02 %. The specific gravity of the soils lies in the range of 2.5 to 2.89. The porosity values range from 0.4372 to 0.6381. The study estimates the hydrological properties of sandy loam as: saturated hydraulic conductivity (0.251 cm/hr), porosity (0.506), field capacity (17.17 %) and wilting point (10.15 %). In the case of loamy sands, these values are - saturated hydraulic conductivity (0.748 cm/hr), porosity (0.466), field capacity (11 %) and wilting point (5.8 %).

The study can be useful in developing numerical models for subsurface flow in unsaturated zone for wide-ranging irrigation and drainage studies and particularly to estimate the irrigation return flow.

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