An integated procedure to determine hydraulic conductivity of sand sediment soil that is characterized by an inclusion of gavel particles and cobbles in sand soil is proposed. Firstly the Guelph pressure infiltrometer (GPI) method to measure the soil permeability of the sand is introduced and extended so that it can estimate unsaturated moisture properties of the soil. Secondly a descriptive cylindrical soil model representing sand, gravel and cobbles, and voids within soil is assumed to determine the hydraulic conductivity of the sand sediment soil. A continuity law of flow discharge through the cylindrical soil model is introduced to derive theoretically a functional relationship of the hydraulic conductivity of the sand sediment soil with both the hydraulic conductivity of the sand measured by the GPI method and the gravel content of the soil. An accuracy of the functional relationship of the hydraulic conductivity is examined by laboratory permeability tests. Finally the GPI method and the functional relationship of the hydraulic conductivity are integrated to determine the soil permeability of the sand sediment soil. A numerical example is given to show an effect of the gravel content of soil on a prediction of storm runoff over the sand sediment soil.