The drainage arrangement
Evidence
18 Dr D Martens, an environmental scientist, gave evidence in the council's case on drainage, water quality, geomorphology and impact on groundwater. The applicant's experts were Dr T Johnson, an engineer with special expertise in water engineering and water quality, Dr M Taylor, an expert on geomorphology, Mr P Nichols and Mr S Roso, drainage engineers, and Dr S Short, an expert on groundwater who was a member of the Illawarra Catchment Management Committee between 1996 and 2000. The following were the main points of disagreement.
· Dr Martens said that the proposed drainage system is not a naturally functioning system and therefore it contravened the DCP. Dr Short agreed that it was an artificial system, but added that the present course of Hazelton Creek also cannot be considered natural, as its geomorphic configuration has been significantly affected by agricultural practices. In his opinion, the proposed channels will recreate the same areas of permanent pools and permeable cobble/gravel zones as currently observed in the creek system. Dr Taylor said that there is nothing of unique geomorphic interest in the current degraded Hazelton Creek.
· Dr Martens said that the proposed drainage channel contained too many weirs. Weirs were undesirable and against government policy. In cross-examination he agreed that the policy applied primarily to non-urban areas. Dr Johnson did not agree that the structures in a drainage channel were properly called weirs, or that the government policy applied to them.
· Dr Martens said that the applicant has not carried out sufficient study to assess the development's impact on groundwater level and quality. Dr Short said that there is a sufficient body of general understanding of potential risk to groundwater from urban development to conclude that there would be no adverse groundwater-related effect on land downstream (ie north of Illawarra Highway). Dr Short was satisfied that the proposal complied with all of the government's policies related to groundwater.
· Dr Martens said that the applicant has not provided sufficient information to assess the geomorphologic impact of the proposed development. Dr Taylor said that the assessment he provided was adequate. They agreed that there would be a decrease in the total flood plain area and the sediment supply to the flood plain north of the Highway. They also agreed that there may be higher flow volumes than existing and therefore the channel is likely to be armed. (In Dr Martens' view this would increase its "unnaturalness", while in the view of the applicant's experts this was the normal outcome of urbanisation.)
· Dr Martens said that the extent of excavation and fill was excessive. Mr Nichols and Mr Roso considered that channelisation and bank protection are necessary in the urban context. The amount of excavation and fill in this proposal is consistent with common engineering practice in land development.
· It was common ground that the quality of surface water discharging from the site would not meet ANZECC guidelines. Dr Martens said that the quality of surface water might not be better than the existing. Dr Johnson disagreed. He pointed out that the Environmental Protection Authority's Guidelines require only that the existing quality should not decline. In defence of his position he pointed out that the catchment was approximately 300 ha, while the area under development was about 80 ha. A large part of the remaining 220 ha continued to be in agricultural use. The development also treated surface water from the adjoining residential estate of Regal Heights, which had no stormwater treatment. It was not the responsibility of this development to treat highly polluted water from the upstream agricultural areas.
· Dr Martens said that the treatment ponds should be off-line rather than on-line, so as to allow surface run-off to stay longer in the treatment ponds. Dr Johnson said that there would be separation between the channel and the ponds in the 1:5 year event, and that this was acceptable. The separation had to be balanced against cost and amenity, namely the height of the bund required.
Findings
19 At the heart of the dispute is Dr Martens' opinion that the applicant should have designed the drainage system by rehabilitating the existing creek. Most of his other criticisms flow from this basic premise. He supported his opinion by reference to the DCP.
20 I do not think that the DCP deals with this issue clearly. The plan shows the creek in its existing location, though not quite as meandering as it now is. In any case, the applicant has proceeded along a different path to designing the drainage system to that which Dr Martens prefers. It may be that Dr Martens' approach has a higher ecological value; however, he has not shown how this is balanced against economic, social and amenity values. I do not think that it can be argued (and I did not perceive Dr Martens to argue) that the channelisation of a creek is an unusual response to dealing with the drainage of a residential suburb. In order to refuse the application on the basis that it adopted a wrong approach, it is not sufficient for the council to show that a better design was possible. It is necessary to prove that the proposed method is unacceptable. In my opinion, Dr Martens has not proved this.