In central Randers the basements had frequently been flooded over a period of time. These floodings were found to be due to insufficient capacity of the area's sewerage system. Another consequence of this was frequent surcharging to the nearby receiving waters, Tyvdalen, from an overflow structure in Aalborg Street. The area's sewerage system is a combined system and it contains a large number of low lying basements which are sensitive to high water levels in the system. The city's consultants carried out a number of MOUSE simulations in order to analyse the problem. On the basis of this, the consultant suggested improving the capacity of the main sewerage system in Aalborg Street - a second pipeline parallel to the existing one should be laid. The central section of the new pipe was suggested to be a ø1200 pipe detention basin.
A manhole with a flow controller was fitted halfway and at the end of the pipe detention basin.
The flow controllers secured the optimal functioning of the pipe detention basin. In choosing this solution the city achieved a considerable reduction in the frequency of basement floodings and surcharges to the receiving waters.
The project is from 1999 and the consulting engineers are Carl Bro A/S.
Randers Shopping Centre is constructed on former farm land and it has 1800 parking spaces, distributed over the Centre's 8,5 ha of open spaces.
2/3 of the stormwater run-off from the parking lot and approx. 1,3 ha roof top run-off is conveyed to an existing ø800 combined sewerage pipe in the nearby Merkurvej (Mercury Street). Although the parking lot is laid out using small concrete tiles and green areas, one would nevertheless expect a considerable amount of run-off from the parking lot.
The capacity of the Merkurvej pipe is 746 l/s. 589 l/s are already used by existing catchments. The run-off from the Centre is estimated to exceed 1100 l/s on average every 10th year. It was therefore necessary to control the storm water run-off from the Centre's parking lot.
The problem was solved in the following way: Each of the two parking lot blocks had installed a subterranean detention basin (viz. 220 and 380 m3). A CY vortex valve controls the run-off from each basin (capacity viz. 123 and 61 l/s). Some extra storage volume is gained by allowing moderate flooding on terrain (on average once every 10th year). The volume gained is viz. 480 and 820 m3 (i.e. twice the basins' volumes!).
The project is from 1997 and the consulting engineers are Abrahamsen & Nielsen A/S.
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