Transport for NSW has provided information to Kangy Angy residents regarding the intercity fleet train maintenance facility hydrology and flood model.
According to the Australian Rainfall and Runoff (AR&R), and the Ourimbah Creek Catchment Flood Study, completed in October, 2013, by Catchment Simulations Solutions, the February, 1992, storm event was the largest noted, and recorded as being between a 50- and a 100-year Average Rainfall Interval (ARI) event, TfNSW has informed residents.
The 2007 (Pasha Bulker) storm was approximately a 20-year ARI event.
“It should be noted that the ARI event relates to rainfall and does not directly relate to the wind/swell events that may have been associated,” a TfNSW statement said.
The statement confirmed that its flood study for the site considered the entire catchment area including areas downstream from the facility.
Residents asked TfNSW to identify the principal points of stormwater discharge when the facility water detention pond is full, and whether excess water would go into Chittaway Creek or north of the facility?
“The water will be pumped from the water detention basin into existing waterways to follow the natural drainage path,” the statement said.
“For Basin 2, the water will be pumped next to the spillway into the existing culvert at the un-named creek next to Turpentine Rd.
“For Basin 1, the discharge is into a spillway into a new channel, which discharges to an existing open channel next to the main north rail line.
“Overflow from the water detention basins will also discharge to the same locations.
The pumps in the water detention basins will be powered primarily by the Sydney Trains power supply.
“The Sydney Trains supply is considered a duplicate point of supply, as it is fed from two different locations in the Sydney Trains network.
“As a backup, there is generator connection point located in the front of the maintenance facility building to address a critical Sydney Trains Substation power failure.
“RailConnect, who are the operators of the maintenance facility, will be responsible for the operation and maintenance of the pumps and back up pumps.”
Residents asked whether the changed ground level of the maintenance facility and movement of stormwater would impact Orchard Rd properties.
“Once the maintenance facility is operational, any water displaced by the facility will be captured on site and directed to the water detention basins.
“In the rest of the areas, the water infiltration and water movement will be unchanged from the current scenario.
“During operation, the disposal of surplus stormwater which is not re-used on site, will be stored and discharged via the onsite water detention basins.”
The flood model was received from Council in January.
Since then, John Holland and consultants have checked the model and continued to incorporate the earthworks and other facility areas into the model.
“These design elements are yet to be finalised, although they are fairly advanced.
“Once the hardstand design is finalised, the model will be updated and finalised.
“The base design flood model is issued by Central Coast Council to ensure that consistent catchment modelling and rainfall data is used.
John Holland verified the model and updated it to reflect the project works.
Central Coast Council will validate the updated flood model on receipt from John Holland.
Statement, Nov 2018
Q&A Resident hydrology briefings, Transport for NSW