A Lot of Rain Fell from the Sky - 4th February 2011

The image below represents a view of what probably happened on the evening of 4th Feb 2011 during the excessive rain-event.

Summary of Events:

• When the Head Street Diversion-Drain exceeded it's 'flow capacity', the 'retardation facility' of the park was triggered.
• The majority of the water flow was 'directed' down the natural course of Elster Creek, through the Golf Course, and through the 'choking-outlet' near St Kilda Street.
• When the total water-flow exceeded the 'limit' of the choking-outlet, the 'excess water' flowed back into the Golf Course and ultimately into the southern area of Elsternwick Park, through the culverts under Bent Avenue.
• It should be noted that the lowest area of Elsternwick Park South (apart from the lake) is located on the eastern side of the park, approximately opposite No. 520 New Street.  Located in this region of the park is a pipe-drain which is apparently designed to drain water from this area, under New Street, to the 520mm diameter drain-pipe under the New Street service-road.
• The evening of the rain-event, a large volume of water also flowed from the south, along the New Street service-road ie. from the vicinity of Head Street.

• From eye-witness accounts, water levels rose rapidly within residential properties inside the 'flood-prone' zone (indicated in the image by the magenta-coloured area). Properties outside this zone were also affected.
• Water levels, in residential properties and Elsternwick Park South, remained very close to their maximum level until just after 11 pm on February 4th.
• Between 11pm and 11:30pm water levels rapidly decreased... "It was like someone had pulled the plug out of a bath!"
• No-one could discover why water levels fell rapidly after 11pm that night!  People are still trying to find out "why?"   ...see below for a possible explanation.

Important Factors to Consider:

1. The Pipe-Drain under New Street from Elsternwick Park South to the pipe-drain in the New Street service-road (approximately opposite No. 520 New Street):
It should be noted that Pipe-Drain under New Street is designed to drain water from Elsternwick Park South to the pipe-drain in the New Street service-road.  Hence, when there is a 'significant level' of water in Elsternwick Park South a LOT of pressure is put on the ability of the service-road pipe-drain to cope with draining the service road, because it is also draining the Park!
2. The Choking-Outlet, on Elster Creek, in the Golf Course near St Kilda Street:
Considering how water levels in the Elsternwick Park and surrounds remained fairly constant for many hours until just after 11pm... and then rapidly decreased in less than 30 minutes, it is a distinct possibility that the choking-outlet (near St Kilda Street) was 'blocked' with debris until about 11pm?  If the 'blockage' was cleared around this time, then it would allow about 30 cubic meters per second to flow from Elsternwick Park and surrounds down the natural course of Elster Creek (through Elwood).  This flow rate would explain the speed at which water levels fell after 11pm.