Abstract: Dewatering apparatus is provided, for use in the treatment of particulate material in water, particularly suspensions of sand in water. The apparatus is also provided with means for classifying sand or like particulate material by size. The apparatus employs a sloped trough extending upwardy from a well having sand and water therein, and with a longitudinally moveable rake being provided, with a particularly novel mechanized raking motion, preferably hydraulically operated. The classifying is done by varying the inflow and consequently the overflow of water through the apparatus, varying the water flow from spray pipes extending along side of the discharge trough, or by speeding up the operation of the apparatus.