Settling Reservoir

settling reservoir

[′set·liŋ ‚rez·əv‚wär]
(civil engineering)
A reservoir consisting of a series of basins connected in steps by long weirs; only the clear top layer of each basin is drawn off.

Settling Reservoir


a tank that is used to separate suspended impurities from liquids by gravity precipitation at decreased flow rates. Settling reservoirs are used, for example, to purify water in hydroengineering complexes, irrigation installations, and water-supply and sewage systems; they are also used in machines and industrial plants to purify such substances as oils and gasoline.

Settling reservoirs in hydroelectric plants and irrigation systems prevent the flow of suspended materials into hydroelectric turbines and irrigation channels. In hydroelectric plants and pumping stations, settling reservoirs protect the blades of hydroturbines and pumps from wear that is caused by particles with diameters of at least 0.25 mm. Such wear can reduce the efficiency of turbines and pumps. Settling reservoirs in irrigation systems prevent channels from silting; as a result, only small particles, which can serve as fertilizer, are washed into the irrigation network by water.

Settling reservoirs are classified according to performance, for example, continuous or periodic; according to the method of gathering the sediment, for example, with hydraulic flushing, with mechanical cleanout, or with a combination of these two methods; and according to the number of chambers, for example, single-chamber and multichamber. The rate of water flow in settling reservoirs varies from 0.25 to 0.5 m/sec, depending on the type and quantity of deposits.

Settling reservoirs in water-supply systems can be horizontal, vertical, or radial, depending on the direction of the main water flow. Horizontal settling reservoirs are used to remove suspended matter: any amount of uncoagulated material in water-purification stations can be removed, while 30,000–50,000 m3 per day is the capacity for coagulated substances. Removal of sediment from horizontal settling reservoirs usually involves perforated baskets or pipes that are located at the bottom of the settling reservoirs. Vertical settling reservoirs are used to settle coagulated, suspended matter in purification stations whose capacity is 3,000 m3 per day. Radial settling reservoirs are used mostly in large water purification stations for preliminary clarification of very turbid waters (turbidity in excess of 2 g/l); they are also used to purify recycled industrial water supplies. Radial reservoirs are equipped with scraping devices that effect continuous removal of precipitated matter (see Figure 1).

Settling reservoirs in sewage treatment plants are similar to settling reservoirs in water-supply systems with respect to design and working principle, but they must include somewhat more complicated devices because of the greater volume of sediment that is precipitated from waste water. Primary settling reservoirs are used to separate suspended materials in the mechanical purification stage, while secondary settling reservoirs are used to separate active sludge in the biological purification stage. Radial settling reservoirs with pumps are usually employed after the sludge has passed through aeration tanks. Waste waters are usually kept in reservoirs for 11/2 to two hours.

Figure 1. Cross section of a radial settling reservoir: (1) central distribution pipe, (2) circular trough, (3) pipe, (4) scrapers, (5) movable frame, (6) sludge collecting well, (7) sludge pipeline


Zamarin, E. A., and V. V. Fandeev. Gidrotekhnicheskie sooruzheniia, 5th ed. Moscow, 1965.
Fedorov, N. F., and S. M. Shifrin. Kanalizatsiia. Moscow, 1968.
Kliachko, V. A., and I. E. Apel’tsin. Ochistka prirodnykh vod. Moscow, 1971.