A method includes depositing, onto a shaker screen, downhole materials and fluids coming to a surface of the borehole as a result of a downhole operation. The downhole materials are separated from the fluids using the shaker screen. Using a radar, an electromagnetic wave is emitted toward a discharge end of the shaker screen or a transit downstream to the shaker. A reflection of the electromagnetic wave reflected off a portion of the downhole materials is detected. A velocity of the downhole materials advancing along the shaker screen toward the discharge end of the shaker screen or on a transit downstream to the shaker is determined. An approximate area occupied by the downhole materials on the shaker screen is determined. A volume of the downhole materials based on the velocity of the downhole materials and the approximate area occupied by the downhole materials on the shaker screen is determined.