Improvement of Settling Basins

Abstract

In 1901 the Davenport Water Company constructed at its main pumping station on the Mississippi River a concrete sedimentation basin with a capacity of 3,700,000 gallons. This basin is somewhat irregular in shape, this being necessary to accommodate it to the available land. Its total length is about 470 feet, its width at the west end 128 feet, and at the east end 67 feet. The average depth of water in the basin is about 12 feet. This basin as built had no division walls or baffles and has been in continuous use since it was built. The water from the river is pumped through a 24-inch cast iron pipe which discharges near the east end of the basin. The sulphate of alumina used as a coagulant, enters this 24-inch pipe beyond the west end of the basin, and the water from the sedimentation basin passes from it to a battery of 12 pressure filters, located in the filter building to the west. The plant has always been carefully operated, and water of an excellent quality has always been furnished, although within a few years after the sedimentation basin was put into operation it was realized that better results could be obtained from it if it were divided into two or more compartments, and plans for such a division were prepared prior to the War. Finally, late in 1922, a plan for a wall dividing the basin transversely into two approximately equal compartments was approved, and in March, 1923, a contract was made for this construction. The division wall was built in September, 1923. A section of the wall shows that it forms a deep narrow trough, the water from the east part of the basin flowing into this trough over the top of the concrete wall which forms a weir. After entering the trough the water flows downward, along the whole length of the wall, to an opening controlled by a 30-inch gate valve at the center of the wall and near the bottom. In an emergency