Effect of Leaching Fraction on River Salinity

The effects of 0.10 and 0.40 irrigation leaching fraction management on amounts of salt precipitated in the soil and river channel and compositions of drainage and river water have been calculated for each of the three river types routed through nine successive hypothetical irrigated valleys. These calculations assume dissolution of CaCO₃ (in the soil) and return of irrigation drainage waters. Rivers undersaturated with CaCO₃ were slightly less saline under low versus high leaching. Rivers saturated with CaCO₃ were unaffected by irrigation management. Rivers saturated with CaCO₃ and approaching saturation with gypsum experienced substantial reductions in salinity under low leaching compared to high leaching. For CaCO₃-saturated rivers, a change from high to low leaching results in a rootzone soil porosity reduction of 0.008% more per year. For rivers that result in the precipitation of gypsum, soil porosity was reduced about 0.08% more per year for low as compared to high leaching.