Situated on an estuary of a major river, one of the largest cities in China has an average annual rainfall of 1100 mm (43 in). The three-month typhoon season, usually with heavy rains from the Pacific Ocean, leaves behind long-term seepage of water on the streets and/or floods households due to inadequate drainage systems and an obsolete pump station from the 1950s. Drainage is important to the city’s downtown district, which are comprised of high-end residential complexes, municipal administrative buildings, foreign consulates and bustling shopping centers.
The city’s largest pump station for combined sewage and rain/stormwater handling underwent an major upgrade, which includes nine Flygt PL 7121/965 propeller pumps and four Flygt CP 3501/835 wastewater pumps. All pumps are arranged in a circular chamber and share the same water sump. The effective inside diameter of the sump is 39 m (128 ft). Used for rain/stormwater handling, the Flygt propeller pumps have an operating range of between 2.5 and 3.5 m³/s (40,000 to 55,000 US gpm) and a head of 8 to 13 m (26 to 43 ft); the highest efficiency of 83% is obtained at a head of 10.2 m (34 ft). The sewage pumps have an operating range of between 1.0 and 1.4 m³/s (16,000 to 22,000 US gpm) and a head of 7.8 to 12.5 m (26 to 41 ft); the best efficiency of 84% is obtained at 11 m (36 ft).