Kystagerparken
Hvidovre Municipality. Self-cleaning basin with vacuum flushing system and flexible flap in Kystagerparken.
As part of Hvidovre Municipality's aim to minimise the number of basement flooding events and to achieve swimming water quality in Kalveboderne (overflow max. twice per year during the swimming season), Hvidovre Municipality has established a 6,000 m3 in-situ cast basin in Kystagerparken at the point where Damhusåen opens out into Kalveboderne.
The basin directly relieves the pressure on a community sewer catchment of approx. 30 red. ha., and indirectly relieves the pressure on a community sewer catchment of approx. 100 red. ha via large auxiliary pipes.
The basin, which was built in 2000, is fitted with 4 flushing paths. The basin is 100% self-cleaning as automatic flushing has been fitted which starts operating every time water has been present in the basin. The 4 paths in the basin are flushed using a vacuum flushing system. The vacuum system is used to such overflow water up into the 4 flushing chambers, each approx. 20 m3 in size, and when the basin is empty the paths are flushed successively with "flushing waves" by trapping air in the chambers. This system is a simple, reliable, tried and tested technology. The vacuum flushing system ensures that no manual cleaning work has to be done down in the basin. All installations can be reached from the ground, and so there are no moving parts submerged in the waste water flow and drainage systems. This ensures the best possible working conditions for operating personnel.
A self-propelled drum screen in the inflow to the basin ensures that screenings and floating matter down to 4 mm are strained out before the water flows into the basin. A flexible flap which provides a variable-height spillway is fitted as protection in respect of a maximum permissible backflow level to upstream basements. The flexible flap is a flexible plate which sag at a predefined load, equivalent to the level which can be permitted upstream. This is secured to a spillway without mechanical parts of any kind. Hence the flexible flap requires no maintenance. The flexible flap permits an overflow which is approx. twice as great as at the same overflow height over a traditional fixed spillway and so maximises utilisation of the storage volume in the pipe system.
The basin is part of a major expansion of the municipality's intercepting system compared with the service level at the time of establishment. In 2003, the municipality adopted a new, more stringent target in respect of permissible backflow in the system, and further expansion is in progress.
Statement from Raoul Roestenberg, Krüger: "A vacuum flushing system is an automatic cleaning system which is simple and extremely reliable, and tried and tested technology with many successful reference projects both in Denmark and elsewhere. The vacuum flushing system ensures that no manual cleaning work has to be done down in the basin. All installations can be reached from the ground, and so there are no moving parts submerged in the waste water flow and basin system. This results in simple operation, maintenance and installation and helps provide the best possible working conditions for operating personnel."
We would like to have here a quotation from Jesper Thyme, or another enthusiastic Hvidovre customer:
Finance
Establishment costs: The basin alone cost approx. DKK 20 million, equivalent to approx. DKK 3,300/m3 at the 2000 level.
Operating costs: Not measured, but limited to power consumption at drain pumps and vacuum pumps.
Operation and maintenance
The basin is fully automatic and connected to the municipality's central SRO system.
Catchment
The direct catchment is approx. 85 ha. in size, and is primarily a residential area. The indirect catchment is approx. 300 ha. in size and has more mixed buildings.
Hydraulic capacity
The basin is designed for 2 pressure relief operations per year.
Storage volume in basin: 6,000 m3
Expected overflow: Maximum approx. 3 000 m3/year (calculated with a safety factor of 1.2).
Treatment
Overflow water is treated before the inlet to the basin with a 4 mm automatic grating. The basin is designed to achieve a minimum SM reduction of 25%.
Location
Located on unregistered land, on Nordre Kystagervej, DK-2650 Hvidovre
Contact
Name: Stig Plessing
Organisation: Krüger A/S, Gladsaxevej 363, 2860 Søborg
E-mail: stp@kruger.dk
Telephone: +45 43 30 01 10
E-mail: kruger@kruger.dk