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A new suburb planned for Canberra's north could heighten the risk of flooding along a section of Canberra's light rail route that was inundated during a one-in-100-year weather event earlier this year.
The ACT government has signed a $126,000 contract with Australian engineering firm SMEC to investigate the risk of flooding on Flemington and Morriset Roads.
Both roads already are prone to flooding and development in the new Gungahlin suburb of Kenny could worsen the situation, the contract signed last month states.
"Flemington and Morriset Roads are key transport routes. Flemington Road for general traffic as well as the light rail, Morriset Road specifically as a heavy vehicle access to the Federal Highway and for some traffic," the documents read.
"The ACT government wishes to identify the capital works required to ensure that light rail service requirements are met on Flemington Road in the future as Kenny development occurs. It follows that if light rail service level requirements are met then other transport types will be protected."
A Transport Canberra spokeswoman said while there are parts of the light rail route known to flood, the project was designed to "achieve sustainable flood immunity" for the tracks, platforms and adjacent roadways.
She also said trunk drainage had been upgraded along the route to stop flooding on private property, and improvements made to the Flemington Road ponds near Mitchell to better protect against flooding from Sullivans Creek.
"This is consistent with key project requirements for responding to existing
potential flooding by completing flood assessment of the design to ensure the light rail is protected from flooding and flood levels are not increased along the corridor," she said.
However this work could be compromised by the development of new suburbs.
The first residents have already begun to move into Throsby, which will one day have 1000 homes.
Kenny will be built to the east of Harrison, and is expected to have 200 homes.
It's about 1.5-2 kilometres away from where the light rail will run along Flemington Road and Sullivans Creek cuts right through the middle.
The suburb is not listed on the government's indicative land release program for the next four years.
However the contract notes the development of the greenfield site could lead to larger peak flows downstream, faster flood peaks and problems with erosion.
The Transport Canberra spokeswoman said any new development must ensure that there is no increase in flooding impacts Flemington Road and light rail.
The Kenny catchment is known to be a high infiltration area during rain, especially in the valley.
Generally, the solution is to replace the catchment storage that's been lost to development by building a new basin, but particular restrictions apply in the case of Kenny.
To develop Kenny and the neighbouring suburb of Throsby in the first place, the ACT government had to identify future conservation areas, which have significantly reduced the developable area.
Basins had previously been proposed upstream of Morriset Road in the Kenny area however these basins are in currently protected areas.
The areas are home to critically endangered woodland and the striped legless lizard.
It's understood these areas will be avoided in any proposed basins put forward.
Much of the Sullivans Creek catchment is now urbanised, leading to increased runoff.
A hydro-geological report of the catchment says it typically receives 600-750mm of rain per year, and concrete channels and constructed wetlands are used to manage drainage.
However the creek broke its banks in February this year after heavy rain, leading to flash flooding, damage and disruption across Canberra's inner north.
Some parts of the city were hit by more than 60mm in just a few hours, and hundreds of people called emergency services for help.
At the time Canberra Metro said the southern sections of the route, from Flemington Road towards the city, were flooded and required an assessment before construction could resume.
A month earlier, the ACT Auditor-General Dr Maxine Cooper had released a report saying there was a risk the stormwater infrastructure in many of Canberra's established areas could not cope with high rainfall, because it hadn't been updated to accommodate urban infill or new estates next to old areas.
She said this put the territory government at risk of compensation claims from residents affected by flooding in areas where the stormwater system was overwhelmed.
Dr Cooper said to prevent flooding, a review should be done of stormwater assets in all established suburbs.
The Canberra Liberals' urban services spokeswoman,