Some builders may be more lax about protecting against erosion on their work sites in Canberra than Queanbeyan, due to a lack of territory government enforcement of erosion and sediment rules.
Such an approach, as well as failures to install erosion controls, also led to the territory being forced to foot a $750,000 bill to fix erosion and sediment run-off at Coombs ponds last year.
A report by the ACT's Auditor-General, Dr Maxine Cooper, has highlighted a number of key failings in the processes for handing over stormwater assets, as well as damage caused to them after hand over.
The report shows that despite a government consultant highlighting the problems back in December 2013, and recommending a 'working group' be established to fix it, "little action" has been taken in the five years' since.
The 2013 Alluvium report said smaller block sizes in new land releases making it hard for builders to store equipment on site, limited parking, and "uncoordinated or irregular enforcement" of good building practices were contributing to the problems.
Some of those issues could be addressed through more enforcement activity and delaying building stormwater assets that were likely to be damaged until later in the construction phase, the audit found.
Staff at transport and city services and the Suburban Land Agency claimed that "because of stronger enforcement" of sediment and erosion rules across the border, builders were "more careful to ensure that their building sites were well managed in Queanbeyan than they were in the ACT".
Both agencies also told the Auditor-General they were open to having their rangers approved by the territory's Environmental Protection Agency to enforce the rules and ensure builders were complying.
The audit found that while the government clear objectives for managing accepted stormwater assets, those aims "may not be met due to deficiencies in the asset acceptance processes and the management of accepted stormwater assets".
Such assets represent the ACT government's second-largest infrastructure base, behind only public housing stock, and some 40 per cent of the assets managed by transport and city services.
The audit also looked at the ACT's existing stock of stormwater infrastructure, finding the condition of stormwater assets in had not been reassessed since those areas had been developed, despite having a known flood risk.
"Where reviews have been completed, recommended augmentation work has not been undertaken in all cases and some of these reviews are no longer current," the report reads.
"Transport Canberra and city services advised that areas where there is a current known flood risk include Fyshwick, Chapman, Duffy, Lyons, Page, Red Hill/Griffith, Weetangera and Barton/Forrest."
The audit also found an increased risk that stormwater infrastructure in many established areas of the city would be "unable to cope with major rain events", because the network had not been augmented to manage higher flows.
Among those areas, the audit cited infill developments, particularly multi-unit high rise towers in established areas, and new estates such as Lawson that was linked to existing networks at Kaleen, Giralang and McKellar.
"The impact of new developments on the existing infrastructure and funding for augmentation of this infrastructure should be considered as part of the development of new estates, but TCCS advised that this is not happening," the audit reads.
"There are no scheduled reviews of the condition of the stormwater infrastructure in established areas.
"To ensure that this infrastructure meets future stormwater needs, there needs to be an ongoing program for the review and augmentation of stormwater assets to alleviate flood hazards due to under‐capacity of drainage systems."
The audit made 17 recommendations including creating a working group, as outlined in 2013, to create a strategy to reduce the damage to accepted assets caused by building and other activity.
It also recommended a host of new measures to improve the management of, and planning for, stormwater infrastructure across the ACT.
No government agency provided any comments for inclusion in the audit report.