Gravel and coarse sand make up significant portions of some environmentally important sediments, but the hydraulic properties of the sediments are typically obtained in the laboratory using only the fine fraction (e.g., <2 mm or 4.75 mm). Researchers have found that the gravel content has a significant impact on the hydraulic properties of bulk soils. Therefore, laboratory experiments were conducted to measure the porosity and the saturated hydraulic conductivity of binary mixtures with different fractions of coarse and fine components. We proposed a mixing-coefficient model to estimate the porosity and a power-averaging method to determine the effective grain diameter of sediments. These were used to predict the saturated hydraulic conductivity of binary mixtures. The proposed methods could describe the porosity and saturated hydraulic conductivity of the binary mixtures for a range of gravel contents, and they were successfully applied to two data sets in the literature.